SAMSUNG 797DF Service Manual Troubleshooting

5 Troubleshooting

5-1 Parts Level Troubleshooting

Notes: 1. If a picture does not appear, Click the Brightness and Contrast button on the front panel, and then increase the value

of Brightness and Contrast.

2. Check the following circuits.

• No raster appears: Power circuit, Horizontal output circuit, H/V control circuit, and H/V output circuit.

• High voltage develops but no raster appears: Video output circuits.

• High voltage does not develop: Horizontal output circuits.

5-1-1 No Power Supply

Check and replace FH1,

D601, IC601 and ZD601.

Check the Voltage at

C605 plus polarity point.

Yes

IC601 Pin 1 waveform is correct?

Yes

The secondary

voltage of T601 is correct?

(Is it same as in the
schemetic diagram)

Yes

Check IC622 (KA78R12) Pin 2?

•

Is the voltage 12VDC?

•

Yes

Done

No

No

No

No

Check and replace FH601, D601.

Check and replace

IC601, ZD601, D603.

Check TR, IC and diode

related to every B+line.

Does 4VDC at Pin 5 of IC201?

No

Check MICOM. (IC201)

Yes

•

Check and replace IC622.

•

Check each IC connected to 12V.

LE17IS/LE19IS/LE19IT 5-1

5 Troubleshooting

5-1-2 DPMS Failure

Check signal source

H/V sync. video signal.

Make No H/V sync.

( That is power off mode).

LED blinks?

Does +12V Line off?

(Check the IC622 output Pin 2)

Yes

Is +14V_V Line off?

(Check the Q625 Collector)

Yes

Does Q622 activate?

Yes

Done

No

No

No

Check IC201 Pin 5

or replace IC201.

Check Q625, D627.

Check IC201 Pin 6

or replace IC201.

5-2 LE17IS/LE19IS/LE19IT

5-1-3 H_Deflection Failure

5 Troubleshooting

IC401 Pin 28 waveform is correct?

1

Yes

2

Q413 drain waveform is correct?

Yes

3

Q401 gate, drain

4

waveforms are correct?

Yes

Q490 base, collector

5

6

waveforms are correct?

WAVEFORMS

No

No

No

No

1. Check that DC 12V is displayed
at Pin 29 of IC401.

2. Replace IC401.

Check Q411, Q412.

Check Q403, Q404, IC401

Check +12VDCline.

Check and replace D406 and Q413.

Check DY connector connection.

IC401, #28

1

CH1 P-P = 10.96 V CH1 RMS = 6.180 V

Q401, Drain

4

Q413, Drain

2

Q490, Base

5

Q401, Gate

3

CH1 P-P = 11.6 V CH1 RMS = 6.944V

Q490, Collector

6

LE17IS/LE19IS/LE19IT 5-3

5 Troubleshooting

5-1-4 S Correction Failure

Check S1 ~ S4 signal.

Refer to the S-correction table page?

S1~S4 signals are correct at

each frequency block?

Yes

Check and replace

C451~C456, Q451~Q454, Q455~Q458.

5-1-5 H_Lin. Failure

IC201 Pin 23 voltage varies with

different H_Lin. DAC values?

Yes

Q459 Emitter voltage varies with

different H_Lin. DAC values?

Yes

No

No

No

Check and replace IC201.

Replace IC201.

Check +7 V line.

Check parts around Q459.

Check L441.

5-1-6 Invariable H_Size

IC401 Pin 28 pulse width

H_Size DAC values?

Yes

Q413 drain pulse width

output duty varies with different

H_Size DAC values?

No

Check and replace IC401, IC201.

No

Check parts around Q411, Q412.

5-4 LE17IS/LE19IS/LE19IT

5-1-7 Abnormal H_Size

5 Troubleshooting

WAVEFORMS

Voltage waveforms at

6

Q490 Collector are correct?

Yes

7

T401 Pin 5 wareform is correct?

Yes

Check parts around

IC401 Pin 15 and 16.

5-1-8 Side Pin or Trap Failure

IC401 Pin 24 output exists?

8

The waveform is correct?

Yes

No

No

No

Repeat the troubleshooting

steps for H_deflection failure.

Replace T401.

Check and replace IC401.

Q490, Collector

6

T401, #5

7

Repeat troubleshooting for

5-1-7 abnormal H-Size.

5-1-9 Para. or Pin Balance Failure

IC401 Pin 24 output varies with

different DAC values?

No

Replace IC401.

WAVEFORMS

IC401, #24

8

LE17IS/LE19IS/LE19IT 5-5