Plasma Y-MAIN board LJ92-01200A

[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,
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

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 ?

[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 ?

[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

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

[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.

[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

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.

[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

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.

[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

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

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

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

[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. ?

[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.

[Zalinar]

Re: Plasma Y-MAIN board LJ92-01200A

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

[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.

[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.