SAMSUNG plasma PS42D4S, no standby, no relay click

[Sraros]

I have this plasma TV doesn't open and the problem is the PSU.

So to begin with:
IC2 (IEC2A280) was blown up and now subtituted
C100, C710=308V
C50=10.5-12V trembling. without the IC it was 60V. Same thing at IC2 pins 7-8
C51=0.sth V

F5 fuse going to the relay was blown and replaced.

I also changed quite a lot of caps in the hot circuit because I found lots of caps exceeding ESR limits.

No diodes seem shorted nearby the chip replaced and in general I don't think there is a short, at least with a light bulb test doesn't light up at all.

A couple more odd things to me: TS1 gets 4.sth V and outputs 100V
All the rest TS get 308V same as my first caps.

Still I cannot get the relay to click and no voltages so far at the pins.
Any suggestions?

[R_J]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

You need to check R2 it is likely open. To check any voltages on the primary side you need the meter on HOT GROUND (C100 -) or B02 negative.
Check if you get STD_5V, this one is measured to cold ground (chassis) This voltage is required before anything else will operate.

For the relay to click you need STD_5V and the PS_ON command

[Sraros]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

R2 is 0.7Ω just a little bit more than 0.5 as in schematics
I thought because the relay doesn't click, that I don't get the standby voltage 5V
Not the other way around.

no STD_5V, no PS_ON voltages. So if I somehow manage to get these voltages going.. Then I will get the relay to close circuit?
I should check maybe also my caps on the cold side..
The voltages I gave I measured as you described R_J, hope you have some more ideas

Edit: C100 is 22uF 450V rating and ESR says 2.7Ω
Not sure if this cap is ok as I have seen so many tables different for ESR ratings

[Sraros]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

I m posting here a photo of the circuitry and measurements I have done maybe sby can help further..

[tom66]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

Check D28 and all output components for short.
This is an old set.

Mostly likely cause is short/overload on the 5VSTB side, followed by a failed IC2.

Check what the Vcc rating for IC2 is. Usually at least 13V required to keep it running so if it's low, that suggests circuit is unable to start - like car with flat battery.

[Sraros]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

D28 reads 130 and 325 with red probe on cathode. One leg up

The IC2 is new, replaced. I put it with a light bulb test to check for any short and I saw the lamp just lighting up for a fraction of a second just when I plugged it in (probably from the inductive current?)
Vcc I will check

[tom66]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

Consider replacing C50. Failure of that can cause failure to start.
Also the softstart cap C51 is a little suspect, voltage seems lower than I would expect. You can try running the set without it - see if it stabilises output. Make sure to replace afterwards, as otherwise IC2 might blow eventually.

[R_J]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

What is the voltage on IC2 (2) FB, Check that ZD900 and the output of the opto are not shorted. Are you getting any voltage on the secondary (C39) even .5 or more volts ?
You are getting 300 volts on ic2 pin 5, correct? and one other thing to check is the resistance of the feedback winding T3S pins 3to 4.

[Sraros]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

IC2 FB is trembling 0.15-1.6V
ZD900 and output of the opto are fine, no short.
Nothing on the secondary, dead 0V.
IC2 pin 5 is also 0! I checked D110 again out of circuit and seems fine...

Just thinking...Is it possible the replacement chip I got is faulty?

[tom66]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

Check the primary coil of T3S isn't open circuit.
If so you will need to rewind the transformer or get a new power board.

[Sraros]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

Thx Tom. I didn't expect that. The T3S is indeed open circuit at the rewind between D110 and IC2 pin 5.
I will try to fix although I never opened a TS again

[tom66]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

It's a pretty unusual failure.
Do check that it hasn't failed at the binding posts on the transformer.

It could have failed if IC2 failed short circuit and burnt the transformer, but even that is fairly rare as the fuse tends to pop before the transformer does.

When/if you wind it, make certain that you replace the insulating tape, and use the correct enameled wire.

[Sraros]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

It's a pretty unusual failure.
Do check that it hasn't failed at the binding posts on the transformer.

It could have failed if IC2 failed short circuit and burnt the transformer, but even that is fairly rare as the fuse tends to pop before the transformer does.

When/if you wind it, make certain that you replace the insulating tape, and use the correct enameled wire.

Yes the original IC2 failed short circuit and popped. The only fuse that was blown was F5 before BD2 but still I guess damaged the TS.

So I opened the TS and found the wire that goes to the leg of the TS leading to the IC2 chip pin5 had only the plastic tube. I tried to scratch open to see if there's wire inside but nothing.

Another thing when I removed top layer I found a wire end loose. But I think it was going to the 5th pin that connects nowhere. I unwinded from it's end 68 windings on the outside layer and reached pin5 and then another wire continues inside the main core.

[tom66]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

Just make sure you keep track of all the windings, counting turns... Otherwise you won't be able to rewind the transformer again. It's very likely only the primary has failed. I would be surprised if any secondary turns failed, but you can verify their resistance.

Note that the Vcc-AUX outputs (one for the IC and one for the power board stuff on the primary) will probably not have much isolation between them and the primary. The secondary will however be very well isolated as there is typically a minimum 3kV standoff between pri-sec windings for isolated outputs.

[Sraros]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

The windings I kept track correctlly. What bothers me was the winding of the pin which doesn't get in contact anywhere in the board. I think it was there for no reason or maybe as a shield? I don't know but for sure didn't lead somewhere.

Can I use normal insulating tape (I don't know the name in English) like we use for the cables instead of it's original insulation? those got completely useless

[tom66]

Re: SAMSUNG plasma PS42D4S, no standby, no relay click

No you need to use proper transformer tape. e.g. https://www.amazon.co.uk/Meters-Adhe.../dp/B00NX4KG7W