Samsung 794MBplus, 796MBplus, 798MB Service manual Troubleshooting

4 Troubleshooting

4-1

4 Troubleshooting

4-1 Parts Level Troubleshooting

Notes: Check the following circuits.

- No raster appears: Power circuit, Horizontal output circuit.

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

- High voltage does not develop: Horizontal output circuits.

4-1-1 No Power Supply

Chirping noise exists?

Check and replace IC601.

Check and replace D601 and

FH1.

Done

No

Yes

Repeating start?

Check and replace D606.

No

Yes

IC601 Pin 1 waveform is

right?

Check and replace IC601.

Yes

No

C627 Voltage is 13 V ±

0.5V?

Check and replace IC201,

IC301, IC401, Q590, Q490,

and 12V regulator circuit.

Yes

Yes

No

Normal operation?

Replace main board.

Verify voltages.

No

WAVEFORMS

1

1

332 Vpp (IC601, #1)

4 Troubleshooting

4-2

4-1-2 DPMS Failure

Make no H/V Sync. (power off

mode)

Check signal source

H/V sync. video level.

LED blinks?

Check IC201 Pin 40.

Yes

No

+12 V line off?

Check IC201 Pin 5/Pin 6 and

Q624, Q625 operation.

No

Yes

IC601 Pin 1 output

voltage exists?

Refer to 5-1-1 no power

supply.

Done

Yes

No

2

2

332Vpp (IC601, #1)

WAVEFORMS

4 Troubleshooting

4-3

4-1-3 H_Deflection Failure

Does horizontal pluse

signal appear at Pin

26 of IC401?

Check IC401.

Yes

No

Does 110 Vp-p signal

appear

at Collector of Q401?

Check Q401.

Yes

No

Check Q590, Q490 and T401.

4

Does PWM output

signal appear

at Pin 28 (B_DRV) of

IC401?

Check IC401.

Check 12 V line.

Yes

No

Does DC 12V appear at

Pin 29 of IC401?

Yes

No

3

4-1-4 S Corr ection Failure

S1~S3 signals are correct at

each frequency block?

Check S1 ~ S3 signal.

Check and replace Q451, Q452,

Q453, Q458, Q457, Q456,

Q455, D451, D452, D453.

Yes

Check and replace IC201.

No

5

3

12 Vpp (IC401, #28)

4

2.00V (IC401, #26)

5

78 Vpp (Q401, Collector)

WAVEFORMS

4 Troubleshooting

4-4

4-1-5 H_Lin. Failure Check and Replace L441 (Fix Type)

4-1-6 Invariable H_Size

IC401 Pin 28 voltage varies with

different B_DRV DAC values?

Q590 gate output duty

varies with different B_DRV

DAC values?

Check some parts around

Q590,

Pin 14~16 of IC401.

Yes

No

Check and replace IC401.

No

4-1-7 Abnormal H_Size

IC401 Pin 24 output duty

varies with different B+

offset DAC values?

Q490 collector

waveform is right?

Check and replace Q411,

Q412, Q413, and Q414.

Check components

around D405 and L411.

Yes

Yes

No

Check and replace IC201,

IC401.

No

6

6

1300 Vpp (Q490, Collector)

WAVEFORMS

4 Troubleshooting

4-5

4-1-8 Side Pin or Trap Failure

IC401 Pin 24 output

exists?

Yes

Check and replace IC401.

Refer to 5-1-7

abnormal

H_Size

.

4-1-9 Para. or Pin Balance Failure

IC401 Pin 24 output varies
with different DAC values?

No

Replace IC401.

No

7

4-1-10 Tilt Failure

IC201 Pin 20 output duty varies

with different DAC values?

Q323 Base output varies

with different DAC values?

Check and replace Q323.

Check and replace Q321 and

Q322.

Yes

Yes

No

Check and replace IC201.

No

Check tilt connector

connection

Refer to 5-1-7

abnormal

H_Size

.

Yes

7

0.44 Vpp (IC401, #24)

WAVEFORMS

4 Troubleshooting

4-6

4-1-11 V Deflection Failure

13V and –10V lines are on?

IC401 Pin 23 output exists?

Check and replace IC401.

Yes

Yes

No

Refer to 5-1-1 no power

supply

No

IC301 Pin 6 output exists?

Check and replace

components around IC301.

Yes

No

Check DY connector

connection.

8

9

4-1-12 V Size or Position Variation Failure

IC401 Pin 23 output varies
with different DAC values?

Yes

Check and replace IC201 and

IC401.

Check and replace IC301.

No

8

2.5 Vpp (IC401, #23)

9

50 Vpp (IC301, #6)

WAVEFORMS