Samsung PS50B5302SW dead

[ProDave]

Samsung plasma tv totally dead.

No standby light (not even sure there is one on this set)

If you put your ear right next to the PSU board you can just hear the very faintest chirp chirp like it's trying to fire up and immediately shutting down.

I take it therefore a replacement psu board will fix it.  Is it likely anything else will have died or just the psu?

[downunder]

Hi ProDave,

That's a huge gamble, assuming it's the power supply. Have you done any other checks. e.g, does it fire up if the scan boards are disconnected from the power supply, is the LED on the control board flashing, is PS-ON pin changing level when you power it on, is standby 5V present all the time the set is connected to the mains? As far as I recall, all Samsungs have a standby light.

[ProDave]

No outputs at all, even with power boards unplugged from PSU.

The only output showing any hint of an output is "PS_ON" hovering between 1.2 and 2.2 volts.

Anyone got a schematic for these power supplies, or even a full service manual for the set?

the power supply board is BN44-00274B revision 1.2

[ProDave]

If I unplug the ribbon cable to the small signal board from the PSU, I get 2.6V on PS_ON and 5.0V on 5V stby

Dead SSB pulling the standby power down?

Another quick test.

SSB unplugged, 1K resistor between 5v stby and ground, pulls 5V stby to less than 1V

So 5V stby won't even source 5mA

So PSU fault or SSB fault?

[ProDave]

Okay some real progress.

Power up 5V stby from bench psu. now for the first time I have the standby light on the front light up.

Try to turn the set on, and after a few false starts (relay clicking) the set powers up and picture is fine.

So it looks like a PSU fault, and clicking relays usually means dud capacitors doesn't it?

Is there a service kit to fix this PSU rather than replacing it?  Can't find one on Ohm supplies.

P.S I have the service manual now for the PSU from Electro Tanya.

[watteau]

Hi,
Sounds like a standby supply fault.
Circuit attached if you need it.
Regards,
John

[ProDave]

Thanks

I had already got the circuit bit it never hurts to post if for others.

This is an odd one that has me foxed.

Initially the 5V standby was all but dead.  After replacing all the electrolytics in the standby circuit the 5V standby is "working" and I have the standby light, but try and turn the set on and thr 5V standby sags and it fails to start up.

I presently have it working on test with a separate little power supply providing the 5V standby.

It's not a capacitor fault as they have all been replaced. It can't be a semiconductor fault, surely if it was the 5V standby would not work at all.

So what else can make the 5V standby "work" but not be capable of sourcing enough current to turn the set on?

[downunder]

Looks very similar to a Panasonic standby circuit I was working on last week. Turned out to be the opto PCM801S, but the reference IC CM401 could conceivably cause it too.         Bruce

[Liam]

I'm having issues with my Samsung psu, take a look at my pcm801s opto
Do you think that this is worth replacing?

[downunder]

The opto doesn't look too healthy, Liam. Is that just dust on the pcb beside it or has an electro leaked?

That would certainly affect the operation OF IC801S which looks to be the control IC for generation of Vs.

Bruce