Samsung PS42Q97HD power problem

[Turnip]

Hi folks,
Have set in using BN44-00194A power board where QS801 and QS802 appear OK and with no dries but VS1 doesn't power up though VS2 does and sound is OK. Checked and there's some 400V on QS801 but nothing on QS802 so suspect a drive problem maybe - Any thoughts ? - Thanks - Chris.

Realise I've put it in the wrong section but the other one seems to have vanished at the moment.

[downunder]

Hi Chris,

Don't mind plasmas, but these are not at the top of my list.

VS1 and VS2?? Is this Turnip-speak for Vs and Va?

Some points to ponder: Vs is activated by the Logic (control) board sending a VS-ON signal (3-ish V) to the power board. LED on logic board must be flashing. VS-ON present at marked pin on PSU?

Y-Main may be shorted. Does Vs appear if Y-Main is disconnected from the PSU?

Top or bottom buffer boards could be duff. Disconnect one at a time from the Y-Main and see if Vs returns and/or one half of the screen lights up. Mainly the top buffer fails.

Food for thought.              Bruce

[Turnip]

Thanks Bruce,

You are as ever correct, don't know where I got VS1 and VS2 from but spent some time comparing various PS diagrams hoping to find the right one. Liked this model (a wee bit) as was most always dries or a burn-up in the QS801/2 area.

This one is as clean as a whistle, and VS doesn't fire up with the plug disconnected. Checked Y/main and buffers but they seem OK with no popped chips or readable shorts.

Checked for a flashing LED but it seems that a board that might be the control board is placed directly under the Main (signal) board and a hefty screen, so not even the board can be seen. Checked VS-ON signal at 3.5v.

Notice that ChasHyde sell repair kits for several PS problems but not this one, also Fleabay offer a service where after replacement of duff PS caps, problem exists on another panel, but possibly on a different power board as there is some variety with this model BN44-00161A or BN44-00194A and possibly others.

CX404(2200/10) was bulging a bit so replaced it, but don't suspect it makes any difference as have changed several before while sorting the usual dry joint biz.

Thanks again - Hate Plasma as there's nothing useful on Fleabay - Chris.

[downunder]

Sounds like power supply then. Here's the schematic BN44-00194A.

Bruce

[Turnip]

Hi Bruce and thanks,

Will peruse - Think first to check QS801 and QS802 to see if they're all they should be - Initial check proved the incorporated reverse diodes OK, but haven't checked if they are still working FETs.

Guess should couple up the scope to check drive waveform, but haven't used one for some while. Have a nice LCD scope but not the courage to try use it for anything.

Thought buy it so might suss Vestel inverter trannie failures, but it's always the trannie, so why bother.

On the upside, have a chum - Bit of an artist, who wants to monitor heatbeats for some sort of presentation, and gave me a bag of Fet microphones to try sort to the purpose. Suspect heartbeats are essentially low frequency, but awful needy - Suggested he might contact when I have some idea how to sort, no ideas yet - Chris.

Have another one coming in tomorrow, but suspect it's the one that just needs it's FET's resoldered, as one alternative power board for this model really troublesome from dries, but profitable.

Was BN44-00162A - 50 inch and just the usual dries - a good earner.

[Turnip]

Hi folks, and thanks again Bruce.

Checked around ICS801(MC33067) and voltages seemed reasonable but there was no drive to the lower output  (QS802) FET gate, so thought it might be a duff ICS801 - and it was, surprisingly.

Still hate plasma but two Sammies done in a week gives a bit of a lift - Chris.

PS - Think a piccy of the area from service data supplied.

[downunder]

 Nice piccy as ever, Chris, and impressed by your fault-finding techniques. The MC33067 eh! I've never changed one of those, but you know what they say........

We'll have you sorting these plasmas out in no time.                Bruce

[Turnip]

Hi Bruce,

Experience has always told me that the chip is never the problem, so I circled around a bit checking those Opto-Isolators, using suitable earths for each, either side of the Hot/Cold biz - got a minor belt just once where I forgot whether I was hot or cold.

Concluded that it must be the chip, but still didn't believe it. But having an old Sammy panel with a couple of such chips on sub-panels thought to have a go.

Still hate plasma, although admit pictures can be good - Chris.