Plasma Y-MAIN board LJ92-01200A

[Cailloux]

Hello, I need help to troubleshoot a Y-MAIN board LJ92-01200A (LJ41-02759A) at the component level.
Prima plasma TV model PH42T7.
Initially, I found the two Y buffers defective, on the Y main a short circuit mosfet Q5009 (One of these 7 transistors in parallel), and a diode short circuit D5022.
D5022 is indentifies F6 5L.
I bought two new Y buffers boards, LJ41-02761A / LJ41-02760A, Q5009 I removed, and installed a 1N4007 diode (1 amp) at D5022.
I have not replaced Q5009 for now.
I installed Y upper board, and the Y main.
Turn on TV for 10 seconds.
Top side of the picture is good and clear.
I removed upper Y board, and installed lower Y board.
Bottom side of the picture is very bad, garbage on screen.
D5022 diode short circuit again. Something kill it.
I checked the Y buffers boards, no short circuit on both.
I tried a second time the same operation with a diode 2 amps, same thing.
What's going on?? All fuses are good.
Another component of the Y main is in fault?
Is it possible that IPM module (the big IC) is defective?
Thank you for help.

[tom66]

Re: Plasma Y-MAIN board LJ92-01200A

You can't replace a high speed surface mount Schottky diode with a general purpose type! No matter how many "amps" it has.

[Cailloux]

Re: Plasma Y-MAIN board LJ92-01200A

Hi Tom,
You're right, I'll get a Schottky diode, but I do not know the values of amperage and voltage.
What is strange is that the diode fail only with the lower Y buffer. She has no short circuit.
I'll keep you informed. Thank you.

[cmj21973]

Re: Plasma Y-MAIN board LJ92-01200A

Hi Tom,
You're right, I'll get a Schottky diode, but I do not know the values of amperage and voltage.
What is strange is that the diode fail only with the lower Y buffer. She has no short circuit.
I'll keep you informed. Thank you.

http://www.marsport.org.uk/smd/mainframe.htm

F6 CMOZ3V9 CSC I SOD523 zener 350mW 5% 3.9V

I'm 80% sure this is what your looking for, but I'd get a second opinion from someone more experience.

[Cailloux]

Re: Plasma Y-MAIN board LJ92-01200A

http://www.marsport.org.uk/smd/mainframe.htm

F6 CMOZ3V9 CSC I SOD523 zener 350mW 5% 3.9V

I'm 80% sure this is what your looking for, but I'd get a second opinion from someone more experience.

In my research, I saw this suggestion in another forum. I do not think it is a zener on the board because it is indentifies D5022, not Z5022. It is connected from the anode to a transformer, and the cathode to a capacitor of 100UF-160v. Seems to be a circuit filter.

[Cailloux]

Re: Plasma Y-MAIN board LJ92-01200A

You can't replace a high speed surface mount Schottky diode with a general purpose type! No matter how many "amps" it has.

Hi Tom,
I tried with a Schottky diode 3A 200V on D5022.
I installed only the lower Y buffer.
The diode shorted again but this time the lower Y buffer also short.
Do you think the Y buffer was defective even though she had no short-circuit at the beginning?
Or is it possible that the bottom screen is defective??
Have a suggestion?

[Cailloux]

Re: Plasma Y-MAIN board LJ92-01200A

Sorry I do not know how to deleted this post.

[tom66]

Re: Plasma Y-MAIN board LJ92-01200A

The Y-main sends the same signal to both boards, so it's likely that you got a defective lower buffer.

[Cailloux]

Re: Plasma Y-MAIN board LJ92-01200A

Finally, problem solved.
Previously I had bought another used Y buffer $50. It was defective, the seller would not refund my money. I have long questioned, about the Y-sus board.

I take a chance, I'm crossing my fingers. I recently bought another used low Y buffer (another $50), and replaced Schottky diode D5022 3A 200V.

TV repair, it cost me $300 ($50 purchase of the TV, a new set of Y buffer $150, two Y buffer used low $50 x 2 = $100, and two Schottky diode.

I added on the back cover two fans on each side.
Tom66 was right, Y-sus was not involved.
Thank you for your cooperation.

[pchung_94565]

Re: Plasma Y-MAIN board LJ92-01200A

Hi, Cailloux,
Just wonder is your TV still working, I've same problem as your describle in post#1.

[Zalinar]

Re: Plasma Y-MAIN board LJ92-01200A

Hi there, Does anyone know what ZD5003 is? Mine is shorted

[Zalinar]

Re: Plasma Y-MAIN board LJ92-01200A

I answered my own question after some research.

It looks like ZD5003 on the Y board is an RLZ18 Zener that is no longer available.

Cross Reference analogue: BZT52C18-7-F 18V 500mW

Available both from Mouser and Digi-Key

Hope this is helpful.

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

Can anyone run through the common faults on a lj92-01200A I have narrowed my problem down to this board but am unable to find anything wrong with it. No bad caps, and none of my zener diodes appear to be shorted. ?

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

The fuse has not blown, and the TV still goes to standby if I install this board without the fuse and no buffers attached.

[freakaftr8]

Re: Plasma Y-MAIN board LJ92-01200A

When samsung lj41-02761 buffers short *check d5018 d5009 resistors r5090 and r5028 on lj92-01200a ysus board along with mosfets under heat sync.*Also sometimes if sustain pulses like a cycling effect check D5022 near small transformer.******

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

My TV uses LJ92-01203a Y Buffers. Does that make a difference from the 02761 Buffers you mentioned. How do I check the mosfets under the heat sink.
Thanks.

[freakaftr8]

Re: Plasma Y-MAIN board LJ92-01200A

No. That is the same buffer. Samsung uses two part numbers on these boards.

As for the mosfets on the ysus. Look at the wider of the two aluminum heat syncs. They are held on by two posts that solder to the board. Hot one with an iron. Get a wooden dowel and pry the heat sync loose. It will have residential glue like substance thay acts as a heat transfer compound to all the mosfets underneath. This will need to be scraped off later as well as the face of the mosfets and have some new heat transfer paste added to each again upon re installation.

Once the heat sync is off remove one leg from each mosfet from the board on each. Read between the pad and the lifted leg and look for a shorted one. Removing the mosfet is a trick thou. Yo u need plenty of heat. U use a 100 w weller solder gun along.with a 30w iron and solder flux.

installing the new MOSFET is even harder. You need to make sure that when the MOSFET is seated on the board it is flat with all the others because if its not the other mosfets will overheat as the heatsink won't touch the other ones it is a real treat to do.

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

No. That is the same buffer. Samsung uses two part numbers on these boards.

As for the mosfets on the ysus. Look at the wider of the two aluminum heat syncs. They are held on by two posts that solder to the board. Hot one with an iron. Get a wooden dowel and pry the heat sync loose. It will have residential glue like substance thay acts as a heat transfer compound to all the mosfets underneath. This will need to be scraped off later as well as the face of the mosfets and have some new heat transfer paste added to each again upon re installation.

Once the heat sync is off remove one leg from each mosfet from the board on each. Read between the pad and the lifted leg and look for a shorted one. Removing the mosfet is a trick thou. Yo u need plenty of heat. U use a 100 w weller solder gun along.with a 30w iron and solder flux.

installing the new MOSFET is even harder. You need to make sure that when the MOSFET is seated on the board it is flat with all the others because if its not the other mosfets will overheat as the heatsink won't touch the other ones it is a real treat to do.

When you say "wider of the two".... There are 3 heatsinks on this y-sus. A very large one; and two smaller ones... one of which is a little longer than the other; is this the one you are referring too ?

I am measuring .5 ohms across each resistor R5028 and R5090. I see they are in parallel, is this affecting their individual readings ? They are labeled red, black, gold, gold; so they should be 2 ohms and in parallel should = 1 ohm ?
Or should I remove one leg to test these resistors individually ?

With my black probe on the stripe of D5018 and red probe on the other end, my meter beeps when on diode/ohms mode. If i reverse the probes it shows nothing.
D5009 does not beep either way I put the probes on it.
Am I testing these diodes properly, or do I need to remove them from the board first ?

In ohms mode: I get 5.8 ohms across D5018 and 2.2 megaohms across D5009

I feel like I'm slowly getting there, and your help is much appreciated.

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

In diode test mode for volts; with black on the stripe of D5022 and red on the other side I get .456v and when I turn them around I get nothing.

When on diode test of ohms mode I get no reading; I did notice that if I keep switching the probes back and forth that D5022 causes my meter to beep (very short) and I must keep reversing them back and forth.

Again, I did this with the diode still on the board, should it be removed first ?

[SevillianSTS]

Re: Plasma Y-MAIN board LJ92-01200A

Just decided to remove one of those 2 resistors.

They both measure 1 ohm individually, and I guess it is brown instead of red, so they appear to be ok.

What are you thoughts on the diodes questioned above ?

Thanks.