Lesson 15 Troubleshooting Basic TV Problems

7/28/2019 Lesson 15 Troubleshooting Basic TV Problems

1/26

INTRODUCTIONWhen entering a customers home with your service order, look for

specific things, depending on the nature of the trouble call. Each dropsystem component is a potential problem, including TV sets, matching

transformers, drop cables, F-connectors, RF switches, VCRs, set-top

terminals, splitters, splices, directional couplers, grounding systems,

traps, and taps. This lesson focuses on problems at the TV set. It teaches

how to identify and correct problems by: (1) inspecting the front and

back of the TV set and its RF and AC connections; (2) using test

equipment (Figure 1); and (3) adjusting TV settings and controls.

INTRODUCTION Page 1

COPYRIGHT - NCTI, INC. TROUBLESHOOTING BASIC TV PROBLEMS

1 ABC

4 JKL

7 STU

2 DEF

5MNO

8 VWX

0space

3 GHI

6 PQR

9YZ

Set-topterminal

TV set

Cable wallplate

TV

input port

VHF/UHF

RF outRF in

Signallevelmeter

TV test set

Measuring RF input level to set-topterminal

Measuring AC voltage at receptacleto check wiring polarity

Checking picture quality on a TV test setDiscovering wrong TV channel dis-played

Figure 1. Troubleshooting TV-related problems.

Lesson Objectives:

Upon successful completion of this

lesson, the student will be able to:

1. Use a DMM to identify ACinput voltage problems at a

set-top terminals convenience

AC outlet;

2. Use a DMM to identify improp-

er wiring at polarized three-

hole, polarized two-slot, and

nonpolarized two-slot AC wall

outlets;

3. Use an AC outlet tester to identify

improper wiring at polarized

three-hole, polarized two-slot,

and nonpolarized two-slot AC

wall outlets;

4. Check for a TV set or set-top ter-minal hot chassis condition or

AC voltage on the drop with a

DMM;

5. Use an SLM to verify proper

RF input levels to the set-top

terminal and TV set;

6. Identify impedance mismatch

problems;

7. Identify and correct TV problems

caused by wrong channel

select ion or wrong antenna

mode and tuner format settings;

8. Identify and correct TV problems

caused by misadjusted fine-tuning controls, channel program-

ming problems, and misadjusted

picture and audio settings;

9. Troubleshoot inherently defec-

tive TV sets; and

10. Troubleshoot inherently defec-

tive TV sets with stereo audio

problems.

Digital multimeter

NTI


2/26

Since the symptoms of the specific type of problem listed on your service

call order form appear in the picture and/or sound, the customers TV

set is the logical place to begin visual inspections and test equipment

measurements. Tuning controls, TV functions settings, channel

selection, coaxial cable connections, and the impedance selector positioncan be visually inspected. Test equipment is needed to check AC input

voltage, a hot chassis condition, and RF input signal levels.

EXAMINING AC INPUTVOLTAGE PROBLEMS

To check the TV sets AC input voltage, first have the customer turn on the

TV set, either at the set-top terminal or the TV set. It is important to have

the customer turn on the TV set. That way, if the set is defective, the

customer and not you feels accountable. If the TV set does not come on,

verify that its power cord is plugged into an active convenience AC outlet on

the rear of the set-top terminal or directly into an active AC wall outlet.

Checking the Set-topTerminal Convenience AC OutletIn Figure 2A, the set-top terminal AC power cord is plugged into an

active AC wall outlet, and the TV set AC power cord is plugged into the

switchable convenience AC outlet on the rear of the terminal. Turn

on the TV set by turning on the terminal. If the TV set does not come on,

ensure that the TV ON/OFF switch is in the on position. If the switch

is in the correct position and the TV set still doesnt come on, use an

analog or digital multimeter (DMM) to verify that 115 VAC +10% is

present at the terminals switchable AC outlet, as shown in Figure 2B.

Page 2 INTRODUCTION/EXAMINING AC INPUT VOLTAGE PROBLEMS

TROUBLESHOOTING BASIC TV PROBLEMS COPYRIGHT - NCTI, INC.

NOTES

Figure 2. Determining why this TV set does not come on and checking AC voltage at the set-top terminal convenience AC outlet.(Courtesy of Scientific-Atlanta Denver Service Center)

Blankscreen

Terminal channelnumber is displayed

TV power switch is on

A

No AC power to TV set even with terminal AC power present

DMMindicates115 VAC

Test leads insertedinto terminalsswitchable ACoutlet

B

Measuring AC voltage at terminal's switchable AC outlet

NTI


3/26

EXAMINING AC INPUT VOLTAGE PROBLEMS Page 3


Checking the AC Wall OutletIf the TV set or the set-top terminal AC power cord is plugged into a

receptacle of an AC wall outlet and the TV set or terminal does not

come on, first look for a wall switch that might control that receptacle.

If this wall switch is found in the off position (Figure 3A), turn it on

and verify that the TV or terminal is now operating properly. If no

wall switch is found, use a DMM to check for 115 VAC +10% at the

receptacle of this AC wall outlet. If there is no AC voltage at the wall

outlet (Figure 3B), check to see if its circuit breakeror ground

fault circuit breakeris either off or tripped. Ask permission to

reset the tripped breaker. Remeasure the AC voltage at the receptacle

and verify that there is 115 VAC 10% (Figure 3C).

A TV set, VCR, or set-top terminal may not function properly becauseits AC input voltage is not within the typical operating range of

115 VAC +10%. If the AC voltage is not within the required operating

range of the electronic device, ask the customer to call a licensed

electrician or the local power company to correct the problem.

NOTES

Switchin offposition

ACoutlet

C

Test leadsinserted in topreceptacle slots

115 VACreading

No AC voltage due to circuit breakertripped

TV set and set-top terminal off because wallswitch has power turned off to receptacle

Verifying 115 VAC +10% after resettingbreaker

BA

Test leadsinserted in topreceptacle slots

0 VACreading

Figure 3. Discovering why there is no power to TV set and set-top terminal and measuring the AC voltage at the receptacle of the TV setsor set-top terminals AC wall outlet.

Review Questions, Part I

1. Why is it important to have the customer turn on the

TV set when you first start troubleshooting?

2. What AC voltage level should be measured at the set-

top terminals convenience AC outlet?

3. What should you look for first if the TV set or set-top

terminal AC power cord is plugged into an AC wal

outlet and the TV or terminal does not come on?

4. What should you check i f there is no AC voltage

measured at an AC wall outlet that does not have a

wall switch?

WARNING!!

Shorting DMM test leads together while

making an AC voltage measurement

can melt test leads, trip a circuit

breaker, or possibly cause an electrical

shock!

NTI


4/26

Page 4 CORRECTING A HOT CHASSIS CONDITION


CORRECTING AHOT CHASSIS CONDITION

It is possible to receive an electrical shock or see a spark while connecting

or removing coaxial cables from the TV set, VCR, or set-top terminal.

These are symptoms of a hot chassis condition, which can be caused

by: (1) improper wiring of apolarized receptacle; (2) cutting the wide

blade on the TV set, VCR, or terminal power cord plug and incorrectly

plugging it into a polarized or nonpolarized AC wall outlet; (3) plugging

an adapter incorrectly into a nonpolarized receptacle; or (4) an

internal problem in the TV set, VCR, or set-top terminal. These

conditions cause an application of AC voltage to the chassis ground.

This section describes how to identify and isolate the cause of a hot

chassis condition at AC wall outlets and customer premises devices.

Checking forImproper Receptacle WiringBefore assuming that the TV set or another customer premises device

is the cause of a suspected hot chassis condition, use an AC outlet

testeror a DMM to verify the AC wall outlet has proper wiring

polarity. Testing procedures are different for each of the three types of

AC receptacles. Always follow your systems policies for testing AC wall

outlets and using grounding adapters with AC receptacles.

Testing a Polarized Three-Hole Receptacle A polarized three-

hole receptacle has two slots of unequal length, plus a third hole for the

AC power cords grounding prong. To check the wiring polarity of a three-

hole receptacle with an AC outlet tester, simply plug the device into the

receptacle, as shown in Figure 4A. Next, check the indicator lights

against the devices chart of test results. Figure 4B is a chart of test

results for a typical AC outlet tester. Always check the chart of test

results for your particular model of tester.

NOTES

DisconnectedAC power cord

Left red and middlegreen lights lit onAC outlet tester

MICR

ONTA

O p e n G r o u n d

O p e n N e u t r a l

O p e n H o t

H o t / G

r o u n d R e v e r s e d

H o t/ N eu t r a l R e ve r se d

C o r r e c t

REASON FORWIRING FAULT

INDICATORLIGHTS FAULT

LEGEND:

Red light Green light Unlighted

Open Ground contactground not connected

Hot and Hot and groundground contactsreversed interchanged

Hot and Hot and neutralneutral contactsreversed interchanged

Correct Receptacle iswired correctly

BA

AC outlet tester indicating hot andneutral wires are reversed in a polar-ized three-hole receptacle AC outlet tester chart

Figure 4. Checking the polarity of a polarized three-hole receptacle using an ACoutlet tester.

WARNING!

If a hot chassis condition is found, do

not proceed with your installation or

troubleshooting unless you can identify

and disconnect the device or AC outlet

causing the hot chassis condition.

NTI


5/26

CORRECTING A HOT CHASSIS CONDITION Page 5


Using a DMM to check wiring polarity requires multiple measure-

ments between different pairs of holes on a three-hole receptacle. A

properly wired polarized three-hole receptacle must have all of the

following: (1) no significant voltage between the long slot and the

ground hole; (2) 115 VAC 10% between adjacent slots; and(3) 115 VAC 10% between the short slot and the ground hole.

A DMM reading of 115 VAC 10% or any significant voltage between

the long slot and the ground hole indicates improper wiring polarity

(Figure 5). No AC voltage between adjacent receptacle slots indicates

no AC input voltage. No AC voltage between the short slot and the

ground hole also indicates no input AC voltage or improper wiring.

Do not connect any AC power cords to a faulty AC wall outlet.

Testing a Polarized Two-Slot Receptacle Check the wiring

polarity of a grounded receptacle with slots of unequal length and no

ground hole with either: (1) apolarized grounding adapterand an

AC outlet tester; or (2) a DMM.

To use an AC outlet tester, first remove the AC outlet wall plate screw

(Figure 6A). Plug the grounding adapters polarized prongs into the

receptacle by inserting the widest blade of the adapter into one long slot

and the narrowest blade into its adjacent short slot. Fasten the adapters

green grounding tab to the receptacle with the AC wall plate screw

(Figure 6B). Plug the AC outlet tester into the grounding adapter

(Figure 6C). Determine the wiring condition by correctly interpreting the

displayed indicator lights according to the chart in Figure 4B on page 4.

Figure 7A (on page 6) shows an example in which the AC outlet tester

center green light is lit. This indicates the polarized two-slot receptacle

is not grounded. In this case, do not use this receptacle to power the TV

set, VCR, or set-top terminal. However, temporarily grounding the

receptacle at this point allows you to further test whether the receptacle

has correct wiring polarity. This knowledge helps determine if the outlet

NOTES

115 VAC+10%on DMM

Red probe in

longest slot

Blackprobe ingroundhole

Figure 5. Using a digital multimeter todetermine that a polarized three-holereceptacle has improper wiring polarity.

B Polarized groundingadapter

Grounding greentab with wall plate screw

AShort slot (normally hot)

Long slot (normally neutral)

Wallplatescrew

C

Widest blade

Grounding adapterNarrowest blade

MICRONTA

OpenGround

OpenNeutral

OpenHot

Hot/GroundReversed

H ot / N e u tr al R ev e rs e d

Correct

Inserting AC outlet tester

AC wall outlet with polarizedtwo-slot receptacles

Installing polarized ground-ing adapter

Inserting AC outlet tester intogrounding adapter

Figure 6. Checking the polarity of a polarized two-slot receptacle using an AC outlet tester and apolarized grounding adapter.

NTI

NTI


6/26



is the cause of the hot chassis condition. To temporarily ground the

receptacle, connect an insulated ground wire between the cable wall

plate connector and the AC outlet wall plate screw, as shown in

Figure 7B. Then check the outlet testers indicator lights again.

If the outlet testers indicator lights show the hot and neutral wires

are reversed (Figure 7B), the receptacle does not have correct wiring

polarity. Do not use this receptacle for powering the TV set or any

other devices. Tell the customer to not use this outlet until it is

repaired by a licensed electrician.

If the outlet tester indicates all wiring is correct, then the hot and

neutral wiring in the receptacle is correct. So long as this receptacle

is temporarily grounded, and if a properly wired AC outlet is notavailable, you may temporarily use the receptacle to power the TV set

and other customer premises devices while you check whether those

devices are themselves causing the hot chassis condition. However, do

not use this receptacle for permanent powering of the TV set or any

other devices. Tell the customer to have the receptacle repaired by a

licensed electrician. Do not plug any AC power cords into an

improperly wired AC wall outlet.

To use a DMM to check the wiring polarity of a polarized two-slot

receptacle, perform and confirm all of the following voltage

measurements: (1) no significant voltage between the long slot andthe wall plate screw; (2) 115 VAC +10% between the long slot and the

short slot; and (3) 115 VAC +10% between the short slot and the AC

wall plate screw. If any of these measurements are not as described,

the AC receptacle is not correctly wired. Do not use it to power any

devices. For example, measuring 0 VAC or near 0 VAC between the

AC wall plate screw and the short slot, as shown in Figure 8A,

indicates either improper wiring or an improper absence of AC

voltage. Measuring 115 VAC +10% between the longest receptacle slot

NOTES

MICRO

NTA

O p e

n

G r o u n d O

p e n

N e u t r a l O

p e n

H o t

H o t /

G r o u

n d

R e v e r s

e d H o t /

N e u t r a l

R e v e r s e d

C o r r e

c t

B

Left red andmiddle greenlights lit

Groundwireclippedtocablewall plateconnector

Ground wire attachedto AC outlet wall plate screw

A

MICRONTA

Open

GroundO

pen

NeutralO

pen

Hot

Hot/

Ground

ReversedH

ot/

Neutral

Revers

ed

C o r r e

c t

Open groundindicator light(one greenlight in center)

Reading open ground indication onAC outlet tester

Temporarily grounding ungrounded polar-ized two-slot receptacle

Figure 7. Using an AC outlet tester to determine a polarized two-slot receptacle has

an open ground, and temporarily grounding the receptacle.

NTI


7/26



and the cable wall plate connector (Figure 8B) indicates that the hot

and neutral wires are reversed. Do not plug any AC power cords

into an improperly wired AC wall outlet.

Testing a Nonpolarized Two-Slot Receptacle A nonpolarized

two-slot receptacle is an older style of AC receptacle that has two

short slots. The wide blade on an AC power cord plug will not fit in

either of the two slots. You may find that the wide blade of the AC

power cord plug on the customers TV set, VCR, or set-top terminalwas cut and plugged into a nonpolarized two-slot receptacle in a way

that either caused a hot chassis condition, blew a fuse, or burned up

the terminal device. Inspect all AC power cord plugs to ensure that

the wide blades are not cut. Ask the customer to have all altered

plugs repaired prior to plugging them back into an AC outlet.

It also is possible to find a grounding adapter with nonpolarized

prongs plugged into a nonpolarized two-slot receptacle in a way that

either caused a hot chassis condition, blew a fuse, or burned up the

TV set, VCR, or set-top terminal. Follow your systems policy

concerning the use of grounding adapters and nonpolarized

receptacles.

To use an AC outlet tester to determine if the grounding adapter is

incorrectly plugged into a nonpolarized two-slot receptacle, unplug

its AC power cord, temporarily install a ground wire between the

AC outlet wall plate screw and the cable ground, and plug an AC

outlet tester into the adapter. Observe the indicator lights on the

tester. If a fault is indicated (Figure 9A on page 8), unplug the

adapter, rotate the prongs 180, plug the adapter into the

NOTES

B One test probeinserted intolongest slot ofpolarized two-slot receptacle

Other test probetouching cablebarrel connector

Measuring 120.8 VAC

Figure 8. Using a digital multimeter to check the wiring polarity of a polarized two-slot receptacle.

ABlack probetouchingwall platescrew

Red probein shortestslot

0.241 VAC reading

DMM set tomeasure ACvoltage

Determining receptacle has improperwiring or no AC

Determining hot and neutral wires are reversed

NTI


8/26



receptacle, and confirm that the tester lights indicate proper

installation (Figure 9B).

To use a DMM to determine if the grounding adapter is correctly

plugged into a nonpolarized, two-slot receptacle: (1) touch the

black test probe to the AC wall plate screw, insert the red test

probe into the right slot (Figure 10A), and verify the reading on

the display is 115 VAC +10%; and (2) touch the black test probe

to the AC wall plate screw, insert the red test probe into the left

slot (Figure 10B), and verify the reading on the display is 0 VAC.

If your measurements match the above readings, connect the

ground wire from the adapter to the AC wall plate screw and

orient the adapter so that its short female slot is on the right asyou plug it in (Figure 10C). However, if the 115 VAC and 0 VAC

readings are reversed, connect the ground wire from the adapter

to the AC wall plate screw and orient the adapter so that its

short female slot is on the left as you plug it in (Figure 10D). Do

not plug any AC power cords into an improperly wired AC

wall outlet.

NOTES

B

Two greenlights on right

Ground wire clippedto barrel connector

A

Ground wire clipped tobarrel connector

Red light on right andgreen light in middle

Grounding adapter improperly installed Grounding adapter properly installed

Figure 9. Using an AC outlet tester and temporarily grounding the receptacle to thecable wall plate barrel connector to check wiring on a nongrounded, nonpolarizedtwo-slot receptacle.

A

V+A

mAA COM

100VMAX

!

320mAMAX

!

10AMAX

! OFF+

~A

~mA/A

~mV

~V

OFFV

mV

mA/A

A

RANGE HOLD

H

V30

0 10 20 30

25MULTIMETERB

V+A

mAA COM

100VMAX

!

320mAMAX

!

10AMAX

! OFF+

~A

~mA/A

~mV

~V

OFFV

mV

mA/A

A

RANGE HOLD

H

V30

0 10 20 30

25MULTIMETERC D

Black testlead

Redtestlead

Nonpolarizedtwo-slot receptacle

DMM

Blacktestlead

Redtestlead

Nonpolarizedtwo-slot receptacle

DMM

AC grounding adapter

ACwallplatescrew

AC grounding adapter

ACwallplatescrew

Measuring AC voltage betweenthe right slot and the AC wallplate screw

Measuring no AC voltagebetween the left slot and the ACwall plate screw

Plugging in grounding adapterif readings match

Figure 10. Determining proper orientation for a grounding adapter on a nonpolarized two-slot AC receptacle.

Plugging in grounding adapterif readings are reversed

NTI

NTI


9/26



Checking for aDefective Electronic DeviceIf a hot chassis condition is suspected and the AC receptacle wiring

polarity is correct, disconnect AC power from one electronic device

at a time to determine which device is causing the hot chassis

condition. Set up and connect a DMM to measure AC voltage

between the cable wall plate barrel connector threads and the

disconnected input coaxial cables F-connector nut (Figures 11A-

11C). When no AC voltage is measured between the wall plate and

the coaxial cables F-connector body, the device that is currently

disconnected from the AC outlet is causing the hot chassis

condition. Repair it prior to using it. Also, use the DMM to check

for voltage between the F-connector nut and the center conductor of

the input coaxial cable when it is connected to the wall plate

connector, as shown in Figure 11D. If AC voltage is present, inform

your supervisor and do not reconnect the input cable.

NOTES

Presence of AC voltage between cable wall plate F-81 barrel con-nector threads and set-top terminal input cable F-connector nutindicates hot chassis condition at terminal

Terminal AC cord

>0 VAC

Terminal input cabledisconnected from wall plate

TV SET OFFTERMINAL ON

TVACpowercord

Out In

TV AC power cord unplugged fromAC convenience outlet

AC voltage present between F-connector nut and center conduc-tor of terminal input cable indicates AC voltage on drop cable

>0 VAC

Cable

disconnected

from terminalinput

connector

TV SET OFFTERMINAL OFF

TVACpowercord

Out In

No AC voltage between terminal input cable F-connector nut andF-81 barrel connector threads at cable wall plate indicates hotchassis condition at TV set

Terminalconvenienceoutlet

Terminal AC cord

0 VAC

TV SET OFFTERMINAL ON

TVACpower

cord

Out In

TV AC power cord unplugged fromAC convenience outlet

Touchingcenterconductor

TouchingF-connector

Presence of AC voltage between set-top terminal input cableF-connector nut and wall plate F-81 barrel connector threads indi-cates hot chassis condition at either the TV set or terminal

Set-top terminalconvenience outlet

75 VHF input

ACoutlet

Terminal AC cord

>0 VAC


TV SET ONTERMINAL ON

TVACpower

cord

Out In


Cablewall plateconnector

A B

C D

75 VHF input

ACoutlet


75 VHF input

ACoutlet


Terminalconvenienceoutlet

75 VHF input

Set-top terminalconvenience outlet

ACoutlet


Figure 11. Determining which device is causing a hot chassis condition.

NTI


10/26



Review Questions, Part II

5. Describe four causes of a hot chassis condition.

6. What two pieces of test equipment can be used to verify

that a polarized receptacle has proper wiring polarity?

7. Describe the three DMM voltage measurements that

indicate a polarized three-hole receptacle is properly

wired.

8. What is indicated by an AC voltage reading of

115 VAC +10% between the long slot and the ground

hole of a polarized three-hole receptacle?

9. How do the s lots d i ffer in a polarized two-s lot

receptacle compared to a nonpolarized two-slot

receptacle?

10. Describe how to temporarily ground a polarized two-

slot receptacle that has an open ground.

11. What should you do if a polarized three-hole or two-slot receptacle is improperly wired with the hot and

neutral wires reversed?

12. How do you determine which electronic device is

causing a hot chassis condition?


11/26

VERIFYING PROPER RF INPUT LEVELS Page 11


VERIFYINGPROPER RF INPUT LEVELS

Low RF input levels to the TV set can cause snowy pictures. High RF

input levels can cause cross-modulation. To measure RF input levels

to the TV set, first disconnect the coaxial cable from the matching

transformer or 75 connector at the rear of the TV set. Then connect

the disconnected coaxial cable to the signal level meter (SLM) RF

input connector and tune the SLM to the video carrier of the set-top

terminals output channel (Figure 12A). Measure the RF video level of

any desired cable channel with the SLM by tuning the terminal to that

desired channel. Tune the SLM to the desired video carrier when the

TV set is connected directly to the wall plate (Figure 12B). The RF

input levels are improperly low in both measurements illustrated in

Figures 12A and 12B. The FCC-required minimum RF level for all

video carriers at the input to the matching transformer or 75 VHF

connector is 0 dBmV. Broadband cable system policies typically specify

a minimum RF level between 0 dBmV and 3 dBmV, and a maximum

RF level between 10 dBmV and 15 dBmV.Always learn and follow

your systems specifications.

NOTES

1 ABC

4 JKL

7 STU

2 DEF

5 MNO

8 VWX

0 spa

ce

3 GHI

6 PQR

9YZ

micr

o MS10

00

+15

+10

+5

+0

-5

-10

-15

-20

TV dBmV

-16.0

67.25

MHZ

dBmV

-31.0

71.75

MHZ

dB

E

F

LEVE

L

Cablewall plate

Select channel 21 inlevel mode

Terminal output cable

1 ABC

4 JKL

7 STU

2 DEF

5 MNO

8 VWX

0 space

3 GHI

6 PQR

9 YZ

micro

MS1000

+15

+10

+5

+0

-5

-10

-15

-20

TV

dBmV

-16.0

67.25MH

Z

dBmV

-31.0

71.75MH

Z

dB

EF

LEVEL

Select

channel 4 inlevel mode

Terminal outputchannel is ch. 4

Terminal istuned to ch. 55

A B

Measuring -16 dBmV RF video level on channel 4 at output of set-top terminal tuned to channel 55

Measuring -10 dBmV RF video level on channel 21 at cable walplate (no set-top terminal is installed)

Figure 12. Measuring improperly low RF levels at the output of a set-top terminal and the output of a cable wall plate.

Review Questions, Part III

13. When checking RF input levels, what video carrier

should the SLM be tuned to when the SLM is

connected to a set-top terminals output cable?

14. What is the FCC-required minimum RF input level for

video carriers at the matching transformer or 75

VHF connector?

NTI


12/26

Page 12 FIXING IMPEDANCE MISMATCH


FIXINGIMPEDANCE MISMATCH

Snowy pictures can be caused by a 75/300 impedance switch

(Figure 13A) or a movable 75 link (Figure 13B) in the wrong

position or by a 75 internal coaxial jumper left unplugged

(Figure 13C). Always place these types of impedance selectors in the

300 position when a matching transformer is installed to achieve

satisfactory picture quality. Place them in the 75 position when

directly connecting the set-top terminal output cable or broadband

drop input cable to a 75 VHF connector.

NOTES

Disconnectedcoaxialjumpercable

Set-topterminal

outputcable

300 VHF antenna

terminals

Matchingtransformer

Link in75 position

300 VHF antennaterminals

Matchingtrans-former

Snowy picture from impedance switch inwrong position

Impedance switch(on back of TV set)

75 coaxial jumper unpluggedMovable link in 75 position

A CB

Figure 13. Examples of an impedance switch, a movable link, and an internal coaxial jumper in the wrong positions, causing snowy

pictures.

300

75 300

75

Review Questions, Part IV

15. When a matching transformer is installed at the VHF

antenna terminals of a customers TV set, what

position should the impedance selector be in?

16. What position must the impedance selector be in when

directly connecting a set-top terminal output cable to a

TV sets 75 VHF connector?

NTI


13/26

RECOGNIZING INCORRECT FUNCTION SETTINGS Page 13


RECOGNIZING INCORRECTFUNCTION SETTINGS

Picture and/or sound quality problems can be caused by the channel

selector position, antenna mode and tuner format settings, fine-

tuning and channel programming controls, or misadjusted picture

and audio settings. Setting these functions incorrectly can cause a

customer to not receive certain broadband cable channels or to see or

hear a wrong channel. Incorrect function settings also can cause beats

in the picture, audio buzz or hiss, too dark or bright of a picture,

unacceptable color or shade of color, or vertical or horizontal

instability. This section explains: (1) how to recognize incorrect

function settings; and (2) how to correctly set the TV adjustments

using manual switches or onscreen menus.

Finding TV ChannelSelector on Wrong ChannelThe most basic setting for a TV set connected to a set-top terminal is

tuning the TV set to the terminals output channel (typically ch. 3 or

ch. 4). If the TV set is not tuned to the set-top terminals output chan-

nel, the wrong channel may be displayed. An example of this problem

is shown in Figure 14, in which: (1) The set-top terminals output

channel is channel 4; (2) the TV set is incorrectly tuned to channel 3;(3) the set-top terminal is tuned to channel 36 (the desired channel);

and (4) the TV set is displaying channel 35 (not the desired channel).

If the customer has a

TV set that automati-

cally tunes to channel 2

when the AC power is

first turned on, explain

to the customer that the

TV set must be manual-

ly tuned to the set-top

terminals output chan-nel. If the customers

TV set has a program-

mable channel memory,

program the TV set to

include the set-top ter-

minals output channel

in the TV sets channel

memory.

NOTES

Terminal out-put channelis ch. 4

Terminalis tunedto ch. 36

Viewing ch. 35

TV tuneron ch. 3

Figure 14. An example of a TV set not tuned to theset-top terminals output channel, causing thewrong TV channel to be displayed. (Courtesy ofAntec)

NTI


14/26

Page 14 RECOGNIZING INCORRECT FUNCTION SETTINGS


Correcting Antenna Modeand Tuner Format SettingsIf a cable-ready TV set without a set-top terminal is not receiving all the

channels provided by your cable system, its antenna mode and/or tuner

format may be set incorrectly. Antenna mode and tuner format may be

separate settings or combined in one setting, and may be set by manual

switches or through on-screen menus, depending on the TV model.

Setting Antenna Mode The antenna mode options for TV sets

typically are listed as Normal/CATV, Antenna/Cable, Air/Cable, or

Antenna/CATV. Acable-ready TV set without a set-top terminal will not

receive all authorized broadband cable channels unless Cable or

CATV is selected as the antenna mode. If the antenna mode is

incorrectly set to Normal (or Air or Antenna), the TV set tunes only

to VHF channels 2-13 and UHF channels 14-69. Setting the mode

correctly to Cable or CATV allows a cable-ready TV set to receive the

proper broadband cable layout of channels, including the nine or more

broadband cable channels in the frequencies between the over-the-air

channels 6 and 7. Figure 15A illustrates setting the antenna mode to

Cable on a TV set that uses on-screen menus, and Figure 15B shows a

TV set with a manual switch for setting the antenna mode.

Setting Tuner Format In some cases it is necessary to change the

TV sets tuner format to receive all offered broadband cable channels.

An incorrect tuner format setting can cause channel reception problems

regardless of whether the TV set is connected to a set-top terminal.

Typical TV tuner formats are Standard, HRC, and IRC. Proper

selection is determined by your broadband cable system. Make this

NOTES

Antenna mode switch(CATV or NORMAL)

BA

Example of using an on-screen menu to setantenna mode to Cable

Figure 15. Examples of using an on-screen menu or a manual switch to set the antenna mode.

Setting antenna modeto CABLE

NTI

Example of a TV set with a manual switch forsetting antenna mode to either CATV orNormal


15/26



adjustment either with an on-screen menu or a manual switch,

depending on the particular TV set. Figure 16 shows an on-screen

menu for a TV set that

combines the antenna mode and

tuner format adjustments intoone setting. For the TV set in

Figure 16: (1) Air/Cable is the

name of the setup menu item

that combines the antenna

mode and tuner format settings;

and (2) Cable IRC is being

selected instead of the other

options (not shown) of

Antenna, Cable STD, and

Cable HRC.

Be aware that some older TV sets cannot receive all the broadband

cable system channels even when the antenna mode and tuner format

are set correctly. In some cases, a TV set labeled cable-ready or

cable compatible may be unable to tune to all of your systems

channels because the TV set has a limited bandwidth. For example,

an older cable-ready TV set that can tune only to channels 2-41

(i.e., 54-330 MHz) cannot tune to the higher frequency channels in a

broadband cable system that transmits channels 2-61 (i.e.,

54-450 MHz) or higher. In that situation, provide a set-top terminal to

allow the customer to receive all your systems channels.

Correcting Fine-Tuningand Programming ProblemsIf a TV sets antenna mode and tuner format have been set correctly but

poor picture quality or channel access problems persist, the cause may

be misadjusted fine-tuning or incorrect channel programming. Channel

fine-tuning problems are more typical of older TV sets, while channel

programming problems are more often a problem with newer TV sets.

Adjusting Fine-Tuning A TV set may require minor fine-tuningadjustments when the TV channel selector is correctly set to the set-top

terminals output channel, but lines (beats) are visible on the TV screen,

as shown in Figure 17A (on page 16). An example of extremely

misadjusted fine-tuning controls is shown in Figure 17B, in which the

set-top terminal is tuned to channel 23, but channel 24 is seen and heard.

To correct these problems on older TV sets that do not have automatic

fine-tuning, adjust the manual fine-tuning controls. Rotary, screw-adjust,

and thumbwheel controls are three kinds of manual fine-tuning controls

NOTES

Figure 16. One example of using an on-screenmenu to set a TV sets antenna mode andtuner format.

NTI


16/26

found on older TV sets. For newer TV sets with automatic fine-tuning but

no manual fine-tuning controls, theAFC/AFT switch in the off position

also can cause misadjustment of the picture.

Correcting Programming Problems The most common

channel programming problem is an available channel not being

stored in a newer TV sets channel programming memory. This causes

the desired channel to be skipped when the channels are scanned

using the channel up or channel down function of the remote

control. Confirm especially that the set-top terminals output channel

is included in a TV sets

channel programming memory.Use the appropriate on-screen

menu to add (or delete) channels

in a TV sets programming

memory. Figure 18 shows an

example of using an on-screen

menu for adding channel 3 to a

TV sets channel programming

memory.

Adjusting Pictureand Audio SettingsA picture that is too dark or too bright may require adjusting the

contrast, brightness, and/or sharpness controls (Figure 19A).

Unacceptable color and/or the shade of color may require adjusting

the color or tint controls. These picture adjustments are made

with either: (1) manual controls typically found on the front panel

of the TV set; or (2) on-screen menu adjustments (Figure 19B).

Page 16 RECOGNIZING INCORRECT FUNCTION SETTINGS


NOTES

Figure 18. Using an on-screen menu to addchannel 3 to a particular TV sets channelprogramming memory.

CCHH.. MMEEMMOORRYY C03 AADDDDEEDD

LANGUAGE

TV SPEAKERS

NTI

Viewing beats in ch. 23


TV tunedto ch. 3

A

Beats in picture, caused by slightly mis-

adjusted fine-tuning


Viewing ch. 24 TV tunedto ch. 3

B

Wrong channel being displayed, caused

by extremely misadjusted fine-tuning

Figure 17. Examples of TV picture problems caused by incorrect adjustment of TVchannel fine-tuning.

NTI


17/26

A vertically unstable (Figure 20A) or horizontally unstable (Figure 20B) TV

picture is another problem that can be caused by misadjusted picturecontrols. Adjust the vertical and/or horizontal hold manual controls to

stabilize the picture. Those TV sets that do not permit external

(nonscrewdriver) adjustment of the vertical and/or horizontal hold require

a qualified TV repairman to correct a vertical or horizontal hold problem.

A buzzing or hissing sound from the TV speaker may result if the TV volume

control is set too high and the set-top terminal remote control volume is

set too low. Correct this problem by lowering the TV volume and then

adjusting the set-top terminal remote control volume to the desired level.



NOTES

Figure 19. An example of a TV picture with misadjusted picture settings and onetype of on-screen menu for adjusting TV picture settings.

TV picture with brightness or contrastout of adjustment

Example of on-screen menu for adjustingTV picture settings

TV picture with vertical hold out ofadjustment

TV picture with horizontal hold out ofadjustment

A B

A B

Figure 20. Examples of TV pictures with vertical and horizontal hold controls out ofadjustment.

}

TV picture settings

NTI

NTI

Review Questions, Part V

17. Explain how incorrect TV channel selection can cause

channel 35 to be seen and heard when the set-top

terminal is tuned to channel 36.

18. What problem is caused if a TV set is connected to the

broadband drop input cable without a set-top

terminal, and the TV sets antenna mode is set to

Air instead of Cable?

19. What are the three typical tuner formats, and what

determines which one should be selected for a

customers TV set?

20. What is wrong when the set-top terminal is tuned to

ch. 23 but ch. 24 is seen and heard?

21. What can cause a buzzing or hissing sound from the

TV sets speaker?


18/26

Page 18 ISOLATING PICTURE QUALITY PROBLEMS


ISOLATINGPICTURE QUALITY PROBLEMS

Sometimes a customers TV set wont operate properly, even after

proper AC voltage and RF input levels are verified, TV impedance

selectors are properly set, and all TV function settings are adjusted. If

the TV sets picture quality is still poor after these adjustments, it is

possible the customers TV set itself is not operating properly. This

section explains ways of using a TV test set to check whether a

customers TV set is faulty.

Using a TV Test Set OnlyOne way to verify that the customers TV set is faulty involves

disconnecting the coaxial cable from the sets matching transformeror 75 VHF connector and connecting it to a TV test set, as shown in

Figure 21. Good picture quality on the test set, with none of the

picture quality problems that were found on the customers TV set, is

evidence that the customer s TV set is faulty.

Another way to determine whether the customers TV set is faulty

involves connecting an antenna or rabbit ears to the customers TV

set and disconnecting the broadband cable. Existence of the same

picture quality problems, with the antenna connection, indicates

the problems are inherent to the customers TV set and are

independent of the cable connection.

NOTES

Cablewall plate

Broadband drop cabledirectly connected toterminal input connector

TV test set tuned to ch. 3

Terminal output cableconnected

to test set's75 inputconnector

Broadband drop cable disconnectedfrom customers color TV set

Figure 21. Checking picture quality on a TV test set.

NTI


19/26

ISOLATING PICTURE QUALITY PROBLEMS Page 19


Using CustomersTV Set and TV Test SetAnother way to check the condition of the customers TV set is to

compare its picture quality with that of your TV test set. Use a two-

way splitter as shown in Figure 22A to compare picture qualities

simultaneously. Poor picture quality on the customers TV set and

good quality on the test set can demonstrate that the customers TV

set is faulty (Figure 22B).

NOTES

Set-top terminal

Customers TV set

TV test set

B

Set-top terminal

Terminal AC power cord

CustomersTV set

TV test set

RF out RF in

Two-way splitter

To subscribers75 VHFinput

To TVtest set

TV setAC power cord

Dropinputcable

TV test set AC power cord

A

Connections for comparing picture quality on customers TV set and on TV testset using a two-way splitter

Comparing customer TV set picture quality to TV test sepicture quality

60 Hz hum baron customersTV set

No hum bar onTV test set

Figure 22. Comparing the picture quality of the customers TV set to that of a TV test set by using a two-way splitter.

Review Questions, Part VI

22. Describe the two ways to use a TV test set to verify

that the customers TV set is the cause of poor picture

quality.

23. How can connecting an antenna to a customers TV

set demonstrate that the customers TV set is faulty?

NTI


20/26

FIXING STEREO TV PROBLEMSWhen a customer does not hear a stereo TV program in stereo on his stereo

TV, follow these five steps: (1) Tune the stereo TV or set-top terminal to a

known stereo TV channel; (2) place the audio mode selector switch or on-

screen audio mode in the Stereo position (not the Mono or Sap

position); (3) determine whether the stereo indicator light is lit; (4) verify

proper balance control settings for left and right speakers; and (5) classify

the type of sound (monaural or stereo) that is coming from the speakers.

If the audio mode selector switch or on-screen audio mode menu is in the

Stereo position but the stereo indicator light is not lit, the sound is

monaural because no stereo signal is available on that channel. On some

stereo TV sets, the stereo indicator light does not light and there is

monaural sound even with the presence of a stereo signal if the audio mode

is selected to Mono or Sap (Figure 23A). On other stereo TV sets, the

stereo indicator light will light, indicating the presence of a stereo signal,

but there is monaural sound from the speakers if the Mono mode is

selected (Figure 23B). It is therefore important to

always ensure that the audio mode is selected to the

Stereo position before concluding why a particular

stereo TV is not producing stereo sound on a known

stereo TV channel. If the balance control is set too far

to the left or right, no stereo separation is heard.

To determine the cause of still not hearing stereo sound after performing

the suggested five steps, connect a stereo TV test set to the broadband

drop input cable either directly or with a two-way splitter. The presence

of stereo sound and a lighted stereo indicator light on only the stereo TV

test set indicates a faulty customer TV set. The absence of stereo sound

from both TV sets indicates a cable system problem.

Stereo indicator light is on but sound is not stereo becauseMONO mode is selected with on-screen programming

B

SAP

POWER

STEREO

Green(Light on)

Red(Light on)

AUDIO MODE

MONO STEREO SAP

Page 20 FIXING STEREO TV PROBLEMS


NOTES

No stereosound

MONO STEREO SAP Stereoindicatorlight notlit

Audio modeselector switch inMono position

A

B

Figure 23. No stereo sound when the stereo indicator light is not lit and when it is lit.

Review Questions, Part VII24. Describe what to check to determine why a customer

does not hear stereo sound on a known stereo TV

channel.

25. What improper adjustments on a stereo TV can

prevent stereo sound?

26. Explain how to connect a stereo TV test set to

determine whether a lack of stereo sound is caused by

a customers defective TV set.

No stereo reception or indication because audiomode selector switch is in MONO position

NTI


21/26

ANSWERS TO REVIEW QUESTIONS Page 21


12. To determine which electronic device is causing a hot

chassis condition, disconnect AC power from one

electronic device at a time while measuring AC

voltage between the cable wall outlet and the

disconnected coaxial input cables F-connector body,

and look for a device that causes a measurement of no

voltage when it is disconnected.

Part III13. When checking RF input levels, the SLM should be

tuned to the video carrier of the set-top terminals

output channel when connected to a set-top terminals

output cable.

14. The FCC-required minimum RF input level for video

carriers at the matching transformer or 75 VHF

connector is 0 dBmV.

Part IV15. The impedance selector should be in the 300

position when a matching transformer is installed at

the VHF antenna terminals of the TV set.

16. The impedance selector must be in the 75 position

when directly connecting a set-top terminal output

cable to a TVs 75 VHF connector.

Part V17. Incorrect TV channel selection can cause channel 35 to

be seen and heard when the set-top terminal is tuned

to channel 36 if the TV channel selector is set to

channel 3 and the set-top terminals output channel is

channel 4.

18. A TV set will not receive all authorized broadband

cable channels if it is connected to the drop input

cable without a set-top terminal and the TV sets

antenna mode is set to Air instead of Cable.

19. The three typical tuner formats are Standard,

HRC, and IRC, and the broadband cable systemdetermines which one should be selected for a

customers TV set.

20. An extreme (not slight) misadjustment of fine-tuning

control(s) is likely to cause channel 24 to be seen and

heard when a TV channel selector is correctly on channel

3 and the set-top terminal is tuned to channel 23.

21. A buzzing or hissing sound from a TV speaker can be

caused by the TV sets volume control being set too high

and the set-top terminals remote control volume set too

low.

ANSWERS TO REVIEW QUESTIONS

Part I1. When you first start troubleshooting, it is important to

have the customer turn on the TV set, because then

the customer and not you feels accountable if the TV

set is defective.

2. A voltage level of 115 VAC 10% should be present at

the set-top terminals convenience AC outlet.

3. First look for a wall switch in the off position if the

TV set or set-top terminal AC power cord is plugged

into an AC wall outlet and the TV set or set-top

terminal does not come on.

4. Check to see if the AC outlets circuit breaker orground fault circuit breaker is off or tripped, if there

is no AC voltage measured at an AC wall outlet that

does not have a wall switch.

Part II5. Four causes of a hot chassis condition are:

(1) improperly wiring a polarized receptacle; (2) cutting

the wide blade of an AC power cord plug and

incorrectly plugging it into a polarized or nonpolarized

AC receptacle; (3) plugging an adapter incorrectly into

a nonpolarized receptacle; and (4) an internal problem

within a TV set, set-top terminal, or VCR.

6. A multimeter (DMM) or an AC outlet tester can verify

the polarity of a polarized receptacle.

7. The three multimeter voltage measurements that

indicate a polarized three-hole receptacle is properly

wired are: (1) no significant voltage between the long

slot and ground hole; (2) 115 VAC 10% between

adjacent slots; and (3) 115 VAC 10% between the

short slot and the ground hole.

8. An AC voltage reading of 115 VAC 10% between the

long slot and the ground hole of the polarized three-

hole receptacle indicates improper wiring polarity.

9. A polarized two-slot receptacle has two slots of

unequal length, while a nonpolarized two-slotreceptacle has two slots of equal length.

10. To temporarily ground a polarized two-slot receptacle

that has an open ground, connect an insulated ground

wire between the cable wall plate connector and the

AC outlet wall plate screw.

11. If a polarized three-hole or two-slot receptacle is

improperly wired with the hot and neutral wires

reversed, do not use the receptacle until it is repaired

by a licensed electrician.


22/26

Page 22 ANSWERS TO REVIEW QUESTIONS/GLOSSARY


Part VI22. To use a TV test set to verify the customers TV set

is the cause of poor picture quality, either:

(1) Disconnect the coaxial cable from the matching

transformer or 75 connector of the customers TV

set and connect it to your TV test set; or (2) install a

two-way splitter to simultaneously compare the

picture quality of the customers TV set to the

picture quality of your TV test set.

23. The occurrence of TV picture problems when the

customers TV set is connected to an antenna

indicates the problems are inherent to the

customers TV set and are independent of the

broadband cable connection.

Part VII24. If stereo sound is not heard on a known stereo TV

channel, check: (1) the selected channel; (2) the

position of the audio mode selector; (3) the condition of

the stereo indicator light; (4) the balance control

setting; and (5) the type of sound at the speakers.

25. Improper adjustments on a stereo TV that can prevent

stereo sound include: (1) the audio mode selector set in

the Mono or Sap position; or (2) the balance control

set too far to the left or right.

26. Connect a stereo TV test set to the drop cable (either

directly or with a two-way splitter) to determine

whether a lack of stereo sound is caused by a

customers defective TV set.

GLOSSARYBelow are definitions of the key terms occurring in bold italic and regular type in the text.

AC outlet tester A device that indicates

condition of wiring in a three-wire AC

receptacle.

AFC/AFT switch The switch on a TV

set that turns on or off the automatic

frequency control, or AFC (which keeps

the TV set closely tuned to the desired

channel frequency) and the automatic

fine tuning, or AFT (which helps a TV set

maintain maximum signal strength forreception of a given channel frequency).

Chassis ground The metal chassis of

the TV set, VCR, or set-top terminal to

which ground connections from its

associated circuit boards and electronic

devices are made.

Circuit breaker A current-sensitive

switch that is placed in series with the

power-supply line to a circuit to remove

power from the circuit if the current in the

line reaches a predetermined value.

Cross-modulation A TV sig na ldistortion that occurs when a desired

channel appears to be modulated by a

strong undesired channel.

Digital Multimeter (DMM) A meter

that permits measurement of voltage,

current, and DC resistance. Also called a

volt-ohmmeter (VOM).

Ground fault circuit breaker The

circuit breaker that trips to remove power

from a circuit that experiences an

unwanted current path to ground on the

output of the circuit breaker.

Hot chassis condition AC voltage

present on the metal chassis of an

electronic device.

Impedance switch The switch on a TV

set that selects either a 75 or 300

input impedance.

Movable 75 link A movable metal

link that causes a 75 input impedance to

the TV set when it is not inserted into the

75 VHF barrel connector and a 300

input impedance when it is.

Nonpolar ized receptacle An ACreceptacle that has slots of equal length

and no ground connection.

Polarity Relative voltage between two

points in a circuit. The black (hot) wire

normally connects to the shortest slot and

the white (neutral) wire to the longest slot

of an AC receptacle. Therefore, there is

normally 115 VAC +10% between the

shortest slot and ground.

Polarized grounding adapter An

adapter that has two polarized prongs,

permits connection of a three-prong plug toa two-slot polarized receptacle, and

provides for continuation of grounding

protection when installed with a grounded

receptacle.

Polarized receptacle An AC receptacle

that has slots of unequal length. The

longest slot is normally neutral and the

shortest slot is normally hot (115 VAC

+10%).

Switchable convenience AC outlet

The AC outlet on the rear of a set-top

terminal that is turned on and off by the

On/Off switch of the set-top terminal.


23/26

TROUBLESHOOTING BASIC TV PROBLEMS

EXAMINATION QUESTIONS FOR LESSON 230-12-1

1. An improper AC input voltage to the TV set is

A. 120 VAC.B. 128 VAC.C. 105 VAC.D. 110 VAC.E. 115 VAC.

2. A polarized three-hole AC receptacle is not properly wired if

A. There is 115 VAC between the short slot and the receptacles groundhole.

B. There is 115 10% VAC between adjacent receptacle slots.C. There is no significant voltage between the long slot and the ground

hole.D. There is 110 VAC between the long slot and the ground hole.E. There are two green indicator lights on an AC outlet tester that is

plugged into the receptacle.

3. A typical AC outlet tester (label facing up)

A. With one green light on in the middle indicates that the ACreceptacle is wired correctly.

B. With a red light on the left and a green light in the middle indicatesthat the hot and neutral wires of the AC receptacle tested arereversed.

C. Requires inserting a grounding adapter with nonpolarized prongsinto a polarized two-slot AC receptacle.

D. Requires only a grounding adapter with polarized prongs to test anonpolarized two-slot AC receptacle.

E. Requires a grounding adapter to test a polarized three-hole ACreceptacle.

4. If a hot chassis condition is suspected at a customer premises installation,A. You can assume that the TV set is the cause of the condition.B. First use a DMM to determine if the TV set or any other terminal

device is the cause of the problem, and then verify the AC wall outlethas proper wiring polarity.

C. And if testing confirms that the TV set is causing the hot chassisproblem, finish the installation by connecting the TV set and tellingthe customer the TV set eventually needs to be repaired.

D. First verify the AC wall outlet has proper wiring polarity, and thenuse a DMM to determine if the TV set or any other terminal deviceis the cause of the problem.

E. And if the AC receptacle wiring polarity is correct, simultaneouslyplug in all customer premise devices into the same AC outlet todetermine which is causing the hot chassis condition.

5. Video RF input levels at the input to the matching transformer or 75 VHF connector of a TV set

A. Should be a minimum of 5 dBmV to comply with FCC requirements.B. Can be measured using an SLM that is connected by a coaxial

jumper to the cable wall plate, even when there is a set-top terminal.C. Should be a maximum of 0 dBmV to prevent cross-modulation.D. Can cause cross-modulation if they are too low.E. Can be measured by connecting an SLM to the set-top terminal

output cable, tuning the SLM to the set-top terminal outputchannel, and selecting the desired broadband cable channel with theset-top terminal.

N

CT

I


24/26

6. There is an impedance mismatch when a TV sets

A. 75/300 impedance switch is in the 300 position and the set-topterminal output cable is connected to the 75 VHF connector.

B. Movable link is in the 300 position and a matching transformer isconnected to the TVs VHF antenna terminals.

C. 75 coaxial jumper is plugged into a matching transformer that isconnected to the TVs VHF antenna terminals.

D. Antenna mode is set to Cable.E. 75/300 impedance switch is in the 75 position and the set-top

terminal output cable is connected to the 75 VHF connector.

7. What can cause a cable-ready TV set without a set-top terminal to onlytune to VHF channels 2-13 and UHF channels 14-69 but not cablechannels above channel 13?

A. The AC wall outlets ground fault circuit breaker is off or tripped.B. The TV volume control is set too high and the set-top terminal

remove control volume is set too low.C. The antenna mode is set to the Normal setting.D. The audio mode selector switch is set to the Sap position.E. The balance control is set too far to the left or right.

8. What can cause channel 20 to be seen and heard when the set-topterminal is tuned to channel 21?

A. The TV tuner is set to the set-top terminals output channel.B. The TV volume control is set too high and the set-top terminal

remote control volume is set too low.C. The channel is being stored in a newer TV sets channel programming

memory.D. The TVs color or tint controls are extremely misadjusted.E. The fine-tuning control on the TV set is extremely misadjusted.

9. Which of the following is a definite indication that a customers TV set is

inherently defective?

A. Existence of the same picture quality problems when the customersTV set is connected to the broadband drop input cable, and when theTV set is disconnected from the cable and connected to an antenna.

B. The TV test set has picture quality problems when it is connected tothe broadband drop input cable in the customers premises.

C. Both the customers TV set and the TV test set have picture qualityproblems when a two-way splitter is used to connect both TV sets tothe broadband drop input cable.

D. Both the customers TV set and the TV test set have good picturequality when a two-way splitter is used to connect both TV sets tothe broadband drop input cable.

E. The customers TV set has good picture quality and the TV test sethas picture quality problems when a two-way splitter is used toconnect both TV sets to the broadband drop input cable.

10. No stereo sound is heard on a stereo TV set if the

A. Audio mode selector is in the Stereo position and the stereoindicator light is lit.

B. Stereo indicator light is lit and the audio mode selector is set forMono sound.

C. Balance control for the left and right speakers is set in the center.D. TV set is tuned to a known and available stereo channel.E. Both C and D.

TROUBLESHOOTING BASIC TV PROBLEMS EXAM 230-12-1

N

CT

I


25/26

Table of Contents

INTRODUCTION .............................................................................. 1

EXAMINING AC INPUT VOLTAGE PROBLEMS ...................... 2

Checking the Set-Top Terminal Convenience AC Outlet

Checking the AC Wall Outlet

CORRECTING A HOT CHASSIS CONDITION .......................... 4

Checking for Improper Receptacle Wiring

Checking for a Defective Electronic Device

VERIFYING PROPER RF INPUT LEVELS .............................. 11

FIXING IMPEDANCE MISMATCH ............................................. 12

RECOGNIZING INCORRECT FUNCTION SETTINGS .......... 13

Finding TV Channel Selector on Wrong Channel

Correcting Antenna Mode and Tuner Format Settings

Correcting Fine-Tuning and Programming Problems

Adjusting Picture and Audio Settings

ISOLATING PICTURE QUALITY PROBLEMS........................ 18

Using a TV Test Set Only

Using Customers TV Set and TV Test Set

FIXING STEREO TV PROBLEMS............................................... 20

ANSWERS TO REVIEW QUESTIONS ........................................ 21

GLOSSARY....................................................................................... 22

Key terms occurring in bold italic and regular type in the

text are listed with definitions specific to this lesson.

This lesson is dedicated to the memory of Jerry Trautwein.

230-12 TROUBLESHOOTING BASIC TV PROBLEMS

Copyright 2001 by Versacom, Inc., dba NCTI, Inc., 801 W. Mineral Ave.,Littleton, CO 80120-4501. All rights reserved. No part of this lesson may bereproduced in any form without permission in writing from the publisher.

Printed in U.S.A.

Special thanks to:

Jim Kuhns, Jim Neil, and Jerry Trautwein.

AT&T Broadband, Comcast Cable, and Dynasty Communications Inc.


26/26

NCTI...Training solutions for the broadband industry

230-12

Lesson 15 Troubleshooting Basic TV Problems

Documents

Transcript of Lesson 15 Troubleshooting Basic TV Problems