SAMSUNG PS42D4S, won't turn on, no standby

[Sraros]

Hello everybody,
I have this plasma TV PS42D4S which doesn't turn on at all. No standby light no clicking sounds nothing. The fuses are all ok, power cables checked and no obvious damage in capacitors. Somewhere to point out to start with?

[Andrew F. Ali]

Re: SAMSUNG PS42D4S, won't turn on, no standby

No clicks and all fuses good and no stand-by light could mean a bad PSU. Without any voltage checks and little information.

[maxvalutech]

Re: SAMSUNG PS42D4S, won't turn on, no standby

Yes and first step is to measure voltage on PSU main capacitor legs DC with neg lead on neg leg and pos lead on pos leg. And of course check continuity of ac lead to set or try another one.

[Sraros]

Re: SAMSUNG PS42D4S, won't turn on, no standby

The whole DC circuit on the PSU is dead. I get no voltages anywhere with or without the main board connected. The two large capacitors in AC are ok at 670V

[dskall]

Re: SAMSUNG PS42D4S, won't turn on, no standby

670v How did you measure that?

[budm]

Re: SAMSUNG PS42D4S, won't turn on, no standby

670v how did you measure that?

+100

[maxvalutech]

Re: SAMSUNG PS42D4S, won't turn on, no standby

Did you measure the two caps individually at 335v ? That still seems low as 370-390v more usual I think. A couple of years ago had a Samsung plasma same problem which was caused on 5v standby line by one of three resistors in series oc - I bridged the three with one larger one of near the same ohms as the three totalled. Followed the circuit back from connector by holding board up to sunlight behind it to identify what components on that line.

[dick_barton]

Re: SAMSUNG PS42D4S, won't turn on, no standby

Do you have 5V (standby voltage STD_5V) at the connector?

[Sraros]

Re: SAMSUNG PS42D4S, won't turn on, no standby

No standby voltage at connector, no voltages in any connector, the complete cold circuit is at 0 voltages. The AC caps are at 310V, I measured with the MM AC voltage and I got the 670V :P. EU power source
Could it be a dead PFC? Just suggesting

[dick_barton]

Re: SAMSUNG PS42D4S, won't turn on, no standby

What voltages do you have at the following points:-
Meter connected between the two legs of C100
Meter connected between the two legs of C710
Check that IC2 (IEC2A280) has not been damaged (blown up) and if not, then check the voltage between pins 7 & 8

Also check the value of C50 and C51 and also R2 (0.5 ohms)

[Sraros]

Re: SAMSUNG PS42D4S, won't turn on, no standby

What voltages do you have at the following points:-
Meter connected between the two legs of C100
Meter connected between the two legs of C710
Check that IC2 (IEC2A280) has not been damaged (blown up) and if not, then check the voltage between pins 7 & 8

Also check the value of C50 and C51 and also R2 (0.5 ohms)

the IC2 is indeed blown! I am amazed, how did you do that!?
Just for the record
C100, C710=310V
C50=60V
C51=0V
R2=0.6Ω

Ok, so replacing it, is fixing the problem or should I expect more damages afterwards? Is there a history on this part or sth that might have caused it?

Thanks dude

[dick_barton]

Re: SAMSUNG PS42D4S, won't turn on, no standby

There was a Youtube video on the set with a similar problem.
Check all the diode in the schematic post #10

[Sraros]

Re: SAMSUNG PS42D4S, won't turn on, no standby

So I went through the whole board today as it's Sunday...
First I am uploading some photos of the back of the board and the manual which I made a searchable PDF for ease although not all text was recognized.

The area of IC2 was already hot marked before I removed the chip since IC2 was blown. Then on the right side I found another hot marked area by the resistors finding shorts in caps C311,313,314,318 leading all the way back to D205 MBR20100CT which is also shorted. The rest seam fine but I uploaded some photos to have an opinion by their looks anyway.

The diodes I measured in diode mode in nearby area of IC2 and in the schematic DickBarton suggested:
D110, D111, D112= 410
D25= 485
D26, D27= 490
D28= 145. Reading bachwards with red lead in cathode 322
D5= 468. Reading backwards 1050
ZD900= 802

The diodes I measured in circuit since I think there were not any in parallel.
The resistors in the red area I measured in circuit and the sum of parallel fit the schematic values.

[dick_barton]

Re: SAMSUNG PS42D4S, won't turn on, no standby

So D205 was short circuit and I'll assume that capacitors measure OK when the diode was removed from the circuit?

[Sraros]

Re: SAMSUNG PS42D4S, won't turn on, no standby

Removing D205 didn't do anything, and also checked the chip and it's fine.
The rest is beyond my understanding.
I have completely isolated the middle pin of D205 from the side legs by removing C318 and R314 and it's still shorted!

[Sraros]

Re: SAMSUNG PS42D4S, won't turn on, no standby

Ok, I figured the connections go on through the top side, so I need to keep looking

[Sraros]

Re: SAMSUNG PS42D4S, won't turn on, no standby

I think I am chasing ghosts and all these removals I made are worthless. The MM is beeping for short but it shows a reading of 32 which is also the total of R412+R413... So, if I am right there's nothing wrong with this part of the board and I am officially a big time noob

[budm]

Re: SAMSUNG PS42D4S, won't turn on, no standby

MM in continuity mode will probably beep with resistance as high as 50 Ohms or more depends on the meter, the 32 display on the meter is probably 32 Ohms. Continuity test will tell you that you have connection between point A and Point B which it does not mean you have shorted circuit, it may be leakage resistance you are seeing. I use Ohm mode to test the suspect circuits/device in both directions to see what kind of resistance I get, if it shows very low resistance like 10 Ohms or so in both directions on the device that I know it should not be then I look first to see if it is connected in parallel with other devices or not (I.E. Diode connected in parallel with 10 Ohms resistor). You will learn as you do more and more troubleshooting. If the part read bad in the circuit then remove it and retest, and even if the part tested good it does not mean it is good because your meter is not putting out the same working Voltage as the device is exposed to in the circuit so it may not show bad with MM but the device will breakdown when it is exposed to the working Voltage.

[Sraros]

Re: SAMSUNG PS42D4S, won't turn on, no standby

I figured it out when I removed a 3W 0.03Ω resistor in series that was in the middle of the circuit and the half from the resistors side was still beeping while the other half not. Thanks for the tips, specially the last part I ll keep it in mind.
One last thing, considered a) all diodes checked fine, an assumption I did since DickBarton didn't mention sth afterwards and b) there's not a short anywhere else... is there a chance that this IC2 blew up because it was itself the problem or damages like this always mean sth else caused it?
I ordered a couple extra of these IC2 but I can cope without any chip explosions

[vinceroger69]

Re: SAMSUNG PS42D4S, won't turn on, no standby

you could replace the ic and use a dim bulb tester as this should save your new ic blowing up https://www.youtube.com/watch?v=UCtz...st=WL&index=44