Samsung PS-42Q97HD Logic Board not giving VS_ON

[tn245]

Hi!

This TV also had the dubious honour of being the subject of the worst soldering job ever thread, but I thought I'd start another thread for some troubleshooting I need to do unrelated to the shocking repair job discussed in that topic.

I've got the PSU working when isolated. Jumpering ps_on and with a resistor between std5v and vs_on I get correct voltages including Vs at 205V.

With everything connected, everything fires up except Vs which stays at 0V, and vs_on which also remains at 0V through the whole start-up sequence. This happens also with any combination of X-main and Y-main connected/disconnected.

I've removed the main AV board and jumpered the logic board for test patterns. Is it supposed to give the vs_on signal itself in this state? Either way I have tried it with forcing vs_on with the resistor and without. With logic board connected without forcing it, vs_on remains at 0V. With forcing it, it briefly rises to about 1.7V and then drops to 0.7V and Vs spikes to 100V or so and then gradually drops down.

The two LEDs on the logic board light up and stay constantly lit.

My guess is I need a new logic board. What are your thoughts?

[tom66]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Vs on will rise only if pson is grounded and the connector between logic and power board is connected.

[tn245]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Yup, I've done it that way. Vs and vs-on stay at 0v.

[tom66]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Do you have 3.3V/5V on that board available at the test points?

[tn245]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Yes I do have 3.3V and 5V at the test points.

[tn245]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Tom I do have 3.3v and 5v at the test points on the logic board.

[tom66]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Can't think of any further tests. Guess you will have to try a new board.

[tn245]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Will do. Thanks. I guess these are pretty specific to the panel and I have to match numbers exactly. None available at the moment that I can find. Will have to wait for one to come up.

[tom66]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

One thing you could try if you've got a scope is to test the oscillator. Also, note you cannot put 50" board in 42" set and vice versa

[flocko]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

board number BN96-06088A can also be used, could help in finding replacement ?

[tn245]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Thanks for the suggestion flocko. I'll add that part no to my searches.

Tom I don't have a scope. Think I might look into getting one at some point though. Are you suggesting other 42" boards might work even with different pba numbers? Or is it the case that you can find boards with the same numbers, but configured for different screen sizes?

This board is LJ92-01496A. Any chance LJ92-01454A would work? There seem to be more of them about.

[flocko]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

well believe it or not i have just got a PS42C96HD with the same problem and the same logic board LJ92-01496A, you can jump the power board to get Vs but no Vs On from logic board also on this one no LED have not had a good look yet just checked fuses and 3.3v and 5v both are there, have not looked for replacement board as could yet find fault,any luck with yours tn245 keep me posted and i will do likewise Flocko

[tn245]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Ah. I will be curious if you come up with anything. I do have two LEDs lit on the logic board, but otherwise the symptoms sound similar.

I have put this one aside for now and am waiting for a chance to grab another board or to come across a broken screen TV with the same board. If you find a fix I would be very happy to hear it.

[andyselectronicstuff]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Hi Guys, just spotted this thread and thought i would let you all know what the problem is, this ctrl board commonly fails after the "Badcaps" in the power supply go bad, the noise on the data lines/supplies causes the 48pin tsop flash chip to become corrupted, it either gives a blank screen as no VS-on from ctrl board or you can get partly blank screen with digital noise. i keep programmed flash chips in stock for this model and the 42in Q96,C97,C96, should anyone need one just pm me.
thanks
Andy
Andys Electronics

[ABMaster]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Hi I've replaced alot of Capacitors on power Supply board
now have all the voltages on the board
but have 2 vertical bars displayed on a black screen ending at the middle of vertical height.
is possible is teh logic LS92-01496A ?'
thanks for a reply
AB

[ABMaster]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

tn245
you can find many logic board on e-bay or aliexpress.com
but can fin more only searching LJ92-01496A
Bye

[andyselectronicstuff]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

Hi I've replaced alot of Capacitors on power Supply board
now have all the voltages on the board
but have 2 vertical bars displayed on a black screen ending at the middle of vertical height.
is possible is teh logic LS92-01496A ?'
thanks for a reply
AB

fault symptoms can vary from blank screen with no Vs-on to something like the image in the attached photos when you have very low Vs-on.

replacing just the flash chip on the control board will cure it.

a new programmed chip is available here if anyone ever needs one.

[flexy123]

Re: Samsung PS-42Q97HD Logic Board not giving VS_ON

wow, excellent, I had an inkling it's something like that, explains why the Logic failed shortly after I repaired the SMPS. Will contact you.