Philips 42MF231D/37 Y-Sustain w/Blown Resistors

[Robb]

My Philips 42MF231D/37 has a bad Y-Sustain and Lower Y-Buffer. The Y-Buffer has only one IC chip that is blown (I think I can handle fixing that). The Y-Sustain, however, appears to have about 15 blown resistors (see photo). Does anyone know how to tell what resistors I need to replace the blown ones and also what other components commonly fail on the LJ92-01200A Y-Sustain? Thank you in advance.

[tom66]

Re: Philips 42MF231D/37 Y-Sustain w/Blown Resistors

How do you know they are failed? Do they test bad?

[Robb]

Re: Philips 42MF231D/37 Y-Sustain w/Blown Resistors

Thanks for responding. With a DMM, the ones that beep on an Ohm test I am guessing are good; the ones that don't beep, I'm guessing are bad.

[tom66]

Re: Philips 42MF231D/37 Y-Sustain w/Blown Resistors

No, that's not how the continuity range works.

Resistors have varying value, the value on them is coded in ohms. Read the value off (look up resistor colour code) and compare to readings on the appropriate ohm range. However, it's rare for resistors to fail without visible marks such burning, discolouration or cracking.

[Robb]

Re: Philips 42MF231D/37 Y-Sustain w/Blown Resistors

Oh, I didn't know that! There are no visible indicators of resistor failure. I will look up the color codes and test, again. That would be nice if the problem is just the Lower Y-Buffer IC chip!

[capkid]

Re: Philips 42MF231D/37 Y-Sustain w/Blown Resistors

You have the dreaded LJ92-01200A Y-Sus and Y-buffer combo problem. I've dealt with this on a few occasions. I believe the usual failure suspect is one of the TA36N30P mosfets under the long, narrow heat sink, but you could have other issues, also. You'll have to at least lift a leg of each mosfet under that heat sink to test them, since they're in parallel.

Do a search for "LJ92-01200A" on the forum, and you should find plenty to read

I had Coppell repair one of my boards, because I didn't have time to deal with it: http://www.ebay.com/itm/Y-sustain-LJ...item255ea6337e

http://blog.coppelltvrepair.com/2010...according.html

[freakaftr8]

Re: Philips 42MF231D/37 Y-Sustain w/Blown Resistors

Yep blown buffers wreak havoc on thise y boards. Like capkid said remove the heat sync pull ine leg on each mosfet. One or more shorted. Replace the shorted one. Look for diodes shorted and open resistors. There will be some.

[Robb]

Re: Philips 42MF231D/37 Y-Sustain w/Blown Resistors

Thanks for the replies. I put the Y-Sustain back in along with the good upper Y-Buffer and the TV displayed the top half of the picture. Does that mean that the Y-Sustain could be good or that just the components going to the good Y-Buffer (upper) are good?

I looked at the long narrow heat sink, but I'm not sure how to remove it properly. I'm going to try to desolder the legs connected to the board on the heat sink and get at it that way, if I don't hear/read any warnings about it.

[tom66]

Re: Philips 42MF231D/37 Y-Sustain w/Blown Resistors

If you get any part of an image the Y-sustain is good, you have a bad lower Y-buffer.

[capkid]

Re: Philips 42MF231D/37 Y-Sustain w/Blown Resistors

It may not be long before your upper goes, which could take out your Y-Sus. With a TV this old, I'd replace the lower Y-buffer and call it done.

[Robb]

Re: Philips 42MF231D/37 Y-Sustain w/Blown Resistors

If you get any part of an image the Y-sustain is good, you have a bad lower Y-buffer.

Thanks, Tom, that's exactly what I wanted to hear. I'm just going to replace the lower Y-buffer IC when it comes in the mail and hope for the best. I also ordered a flux pen to facilitate the soldering of the IC. I'll post back next week with a follow up. Thank you all!

[Robb]

Re: Magnavox 42MF231D/37 Y-Sustain w/Blown Resistors

If you get any part of an image the Y-sustain is good, you have a bad lower Y-buffer.

WIN!!!!!!! My first TV repair!!! You nailed it, tom66! After ripping some pads off the Y-buffer trying to replace the IC that had failed, I bought a used y-buffer and I'm very happily playing Black Ops 2 right now and the picture quality is better (colors brighter) than my Hitachi 42EDT41 - which isn't really saying that much though I was quite impressed at first due to it being my first plasma.

I was a little concerned that there was going to be some other issues as I think CoppelTVRepair said the Y-SUS and other Y-buffer usually go when one buffer goes but everything is looking good for now...it's been on a few hours.