Plasma Y-MAIN board LJ92-01200A

[freakaftr8]

Re: Plasma Y-MAIN board LJ92-01200A

D5022 and 5009 sounds good. pull d5018 and test off board

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

D5022 and 5009 sounds good. pull d5018 and test off board

I pulled one side of the D5018 up off the board, then put my black probe on the striped side of the diode and the red on the other. On diode test volts I get .460 volts and when I reverse the probes I get O.L.
If I've read things right, that diode is OK.

I put my meter on diode ohms test and touched the two pads that the diode usually sits on and I get a beep; meaning the two pads are connected somewhere.

Do you still think I need to remove the heatsink and mosfets ? If so could you verify which one exactly.

Thanks again.

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

Also wanted to mention that the tv only goes to standby when the CN5004 ribbon cable is plugged into the y-main.

[freakaftr8]

Re: Plasma Y-MAIN board LJ92-01200A

Yes test mosfets. I think you will find one shorted

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

I have one MOSFET that is shorted Gate to Drain.

Any tips how to remove this Mosfet ?

Also, any tips to getting the dried paste off the mosfets and heatsink. I tried some rubbing alcohol, didn't do much.

Anything else I need to check for while I wait for the new mosfet to get here.

Lastly, any advise on reattaching the new one ?

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

Ok, actually had 2 mosfets with the gate shorted to the drain.

Are there any tests I can do to the board while I wait for parts ?

Can I put it in the TV without the buffers to see if it will stay on vs. go to standby ?

[PL519]

Re: Plasma Y-MAIN board LJ92-01200A

Hi,
I cannot answer your latest questions but i have the exactly same issue here with this y-main. Found one IC (U5406) shorted on the upper y-buffer. After unsoldering the IC i connected both buffers and the y-main with the rest and fired up the set (btw: Philips 42PF5331/10 - chassis LC4.41E AA) expecting the tv to show up a -distorted- picture. Screen totally dark with green led on front continously green (no blink). Following the repair tips from freakafter8 i measured R5090/5028 and D5009/5018 with component tester in my scope. All o.k. except D5018 which measured shorted (6 ohms with dmm in both directions). Unsolderd D5018: o.K.. Tested mosfets underneath both heatsinks: all good, no shorts.
Regarding D5028 i agree with you, there must be a connection between the two pads but it´s hard to determine where it comes from. This board seems to have at least 4 layers.
@freakafter8: is the reading of 6 ohms normal or is this a hint to a faulty component in this area? What else can we check?
@SevillianSTS: maybe we can compare some of our measurements just to rule out we are locking in the wrong direction?
Wolf

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

Ya sounds good to me, PL519.

I'm just waiting on MOSFET's to arrive. I'm just curious if I need to test anything else before I turn it back on.

[PL519]

Re: Plasma Y-MAIN board LJ92-01200A

Hi,
pretty good question! I´ve read and learned alot from reading different posts in this excellent forum. I take my hat off to all the plasma and lcd gurus here! Great job and thanks!
I myself have abt 30 years of experience with crt tv´s, now getting familiar with lcd´s, but plasmas are still a book of seven seals to me. This one stood in my garage for abt 3 years, not knowing if it is worth the time to look for. Anyway, with the help of this forum i gave it a try and let´s see what happens.

While you are waiting for the mosfets maybe you can prepare the heatsinks for remounting. Same here, the thermal compound is as hard as a stone, no way to get it off with alcohol or something like that. I used a sharp scalpel to scratch it off. Worked fine for me but be careful not to make any deep scratches into the surface of the heatsinks. Did the same with the residue on the mosfets.

Did you encounter any probs with your buffer boards? I could locate one defective driver ic on the upper y-buffer board after removing those little heatsinks on them. The defective one had a little hole on its surface and after removing it from the pcb the resistance between supply rail and ground measured good.

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

Hi,
pretty good question! I´ve read and learned alot from reading different posts in this excellent forum. I take my hat off to all the plasma and lcd gurus here! Great job and thanks!
I myself have abt 30 years of experience with crt tv´s, now getting familiar with lcd´s, but plasmas are still a book of seven seals to me. This one stood in my garage for abt 3 years, not knowing if it is worth the time to look for. Anyway, with the help of this forum i gave it a try and let´s see what happens.

While you are waiting for the mosfets maybe you can prepare the heatsinks for remounting. Same here, the thermal compound is as hard as a stone, no way to get it off with alcohol or something like that. I used a sharp scalpel to scratch it off. Worked fine for me but be careful not to make any deep scratches into the surface of the heatsinks. Did the same with the residue on the mosfets.

Did you encounter any probs with your buffer boards? I could locate one defective driver ic on the upper y-buffer board after removing those little heatsinks on them. The defective one had a little hole on its surface and after removing it from the pcb the resistance between supply rail and ground measured good.

yes, the lower y-buffer has a shorted IC

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

Got all the paste cleaned up.

I then retested to double check...

I have one mosfet that reads 1.3 ohms between Gate and Source
It reads 100.1 ohms between Gate and Drain
It reads 99.2 ohms between Drain and Source.

Does this one need replaced too ?

[tom66]

Re: Plasma Y-MAIN board LJ92-01200A

Yes it's very dead.

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

Once I remove this 3rd, bad mosfet, can I plug the board in to see if it will "not" trip the tv into standby, or is that going to harm something else with out the mosfets attached ?

[tom66]

Re: Plasma Y-MAIN board LJ92-01200A

It's not a good idea to run the board without certain parts unless you're sure no damage will occur.

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

Got my 3 new mosfets installed. Didn't do too bad getting them straight and flat.

Plugged the board into the TV with no buffers.
It still clicks on, then off and the green LED flashes.

I don't appear to have any shorts across either of the 2 black connectors. I checked the few hot pins vs all the ground pins on each connector.

I did notice that my new mosfets measure O.L. from the Gate to Source and from Gate to Drain. The existing mosfets measured about 14M ohms Gate to Drain and 2-5M ohms from Gate to Source.
The New and Existing mosfets all measured about 6.37M ohms Drain to Source. None of them make the meter beep though when on diode check mode for ohms.

So, what do I need to check next ?

[tom66]

Re: Plasma Y-MAIN board LJ92-01200A

Do you have VS reaching the Y-main board?

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

I get 194.5 at the black wire in the power connector on the y-sus for a brief moment and then it goes away once the TV clicks to standby.

If I do not plug in the small ribbon cable below the power connector on the Y-sus, it will stay on and read 194

Whats next ? =)

[tom66]

Re: Plasma Y-MAIN board LJ92-01200A

Where does the small ribbon cable go?

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

Where does the small ribbon cable go?

It is the small cable below the power cable connector.
I am assuming the ribbon cable is a signal / controller cable, while the other is power.

[tom66]

Re: Plasma Y-MAIN board LJ92-01200A

OK, yes, that makes sense, it is for the control/logic board.
Since the voltages disappear if that is connected, I expect you still have a fault on your Y-main.