Philips 42PF5321D/37 wSamsung S42AX panel Y-Main repair

[steves7839]

Hello, I've got this TV which contains the Y-Main and Buffers reputed to short each other out. [LJ92-01200A, LJ92-01202, and LJ92-01203].

I've read the Coppell TV blogs and several threads here regarding how to diagnose these three.

I know the lower buffer is shorted power to common. Too many SMD pins to repair myself. I installed the Y-Main with just the good buffer. The TV still shuts itself off, so I know the Y-Main also has a failure.

I will attach photos of the Y-Main and the area I'm troubleshooting.
I understand from reading Coppell's blog that the shorted fet would read a lower resistance Gate to Drain than good FETs, but only lower by 100 or so ohms.

I put black probe on Common and red probe on each of the low-value resistors in the gate curcuit. Gate to Drain resistance readings on the Y-Main with Y-Buffers disconnected:

Resistors near the Upper Y- Buffer which appears good:
R5085 98.4 Kohms
R5091 98.5
R5092 98.6
R5029 99.3 Kohms


Resistors near the bottom Y-Buffer which is shorted:
R5100 98.5 Kohms
R5101 97.6
R5103 99.7
R5102 97.1 Kohms

Coppell writes that the shorted fets will just read 10-100 ohms below the others. So it looks like R5101 and R5102 are connected to the gates of bad fets. I read elsewhere that the 1" by 3" heatsink is a bear to remove.

I also found two power diodes on heatsinks, D5012 and D5013 read a short between the outer two of three legs. Other diode check readings look like a diode or OL.

Any concurrence of opinion or suggestions?

[steves7839]

Re: Philips 42PF5321D/37 wSamsung S42AX panel Y-Main repair

To simplify the question, can anyone tell me this:
If I install a good Y-Main PCB LJ92-01200A and one good buffer board, leaving the shorted buffer board out of circuit, will the set stay on or go into shutdown?

[steves7839]

Re: Philips 42PF5321D/37 wSamsung S42AX panel Y-Main repair

I powered up with a new used Y-Main pcb and the one good Y-buffer board. The TV stayed on about a minute without going into shutdown. It showed picture on the half with the good buffer. It looks like I'm on the right track if I can find a good lower Y-buffer board LJ92-01203.

[Andrew F. Ali]

Re: Philips 42PF5321D/37 wSamsung S42AX panel Y-Main repair

Yes..You are going in the right direction...

[steves7839]

Re: Philips 42PF5321D/37 wSamsung S42AX panel Y-Main repair

Thanks, Andrew!

I got a lower buffer at a good price on Ebay but it also has one shorted buffer IC.
I've ordered a hot-air station. I plan to try to replace two shorted buffer chips out of the six.

Does anyone know what part number to order?

[steves7839]

Re: Philips 42PF5321D/37 wSamsung S42AX panel Y-Main repair

... if I can find a good lower Y-buffer board LJ92-01203.

... that's not shorted!

[steves7839]

Re: Philips 42PF5321D/37 wSamsung S42AX panel Y-Main repair

... that's not shorted!

Got two from Payless Components on ebay. Good folks! They replaced the shorted board with a good one within days.

Another dead plasma roars back to life!

[ReeceyBurger123]

Re: Philips 42PF5321D/37 wSamsung S42AX panel Y-Main repair

Good job

[steves7839]

Re: Philips 42PF5321D/37 wSamsung S42AX panel Y-Main repair

I've replaced a few suspect parts on the defective Y-Main board that came with the TV. I've replaced Q5011 and a capacitor that was improperly soldered. (The set works fine with the same Y-buffers and a used Y-Main I bought for it)

The TV works with sound and no picture. It doesn't appear to have any backlight.

Ohms checks look OK and there is Vsus of 202V on the Y-sustain. The anomaly is that when I probe any of the FETS Q5005-Q5011, the audio cuts out.

I've examined the service manual for this panel and can't make head or tail of it. No callouts for Vsus or any other voltage higher than the audio 12 and -12VDC. The heatsink over the 7 FETS on the Y-Main is still removed so I can troubleshoot. What voltages should I expect at the FET drains and sources? What section of a y-main is responsible for the panel picture?