AUO t-con - Help me identify and replace transistor please!

[lookimback]

Re: AUO t-con - Help me identify and replace transistor please!

I know its probably redundant to say now but I've done a number of AS15 replacements (the worst being the HF version with the ground pad underneath). What I do is, after tacking the corner pins, drag the solder (and not a lot either) across and use a wick to suck up the excess. I prefer 0.15 dia. Most important though is that I always inspect the chip thoroughly with my magnifier before I try it in the TV. I'm not just looking for bridging on the surface but also behind the pins. Sometimes I have to add more solder and then wick it up when I have bridging behind the pins and can't get it. I'm planning on getting a USB microscope which I think will make it easier too.

[T30M31]

Re: AUO t-con - Help me identify and replace transistor please!

The Toshiba SSM6J212FE which is a P-channel MOSFET appears to have the correct pin-out for this application. I don't know the physical size of Q302 or it's electrical specifications so I can't say for sure this would work.

[tn245]

Re: AUO t-con - Help me identify and replace transistor please!

So I installed a new pnp transistor, which thankfully didn't explode, but.. there seem to be other things wrong with this board.

I have 12V at either end of F1, but Vcc, VGL, VGHC are all 0V. There are other voltages present around the board though. Gamma Vs are there, AVDD=11.6V, VGMA_REF=11.5V to take a few points at random. Both big voltage regulators on board have 0V on all pins.

I found one part shorted. Q302 (centre of attached pic) - a six pin package. A MOSFET I guess?? Marking is 25801, but I think again an in-house number - on the other board I have, the same part is marked 25731. It has about 4 ohms pin 3-4 and to the other 4 pins which are all connected together on the PCB. On the working board it's 47k pin 3-4 as expected with R330 in parallel.

Any ideas of a good substitute? As I said I have a working but slightly different version of this board to make comparisons with.

Thanks for any help!

[tn245]

Re: AUO t-con - Help me identify and replace transistor please!

Nice! I've got a BC327 in a TO-92. Also have one or two BC858B in SOT-23 I could salvage off dead boards I've got here.

I've run out of 3A fuses for this board though so have to order some more before I can get it going. So thought I might throw some MMBT3906 in the order for a tidy repair. What do you think?

[budm]

Re: AUO t-con - Help me identify and replace transistor please!

Do you have any PNP in your stock? It can be TO-92 case style such as 2N3906. I use lots of TO-92 for repair if the board has enough room, for example: http://s807.photobucket.com/user/bud...tml?sort=3&o=1

[tn245]

Re: AUO t-con - Help me identify and replace transistor please!

Ok, so I figured out you meant that the short to ground is what caused the transistor to burn. I've removed and refitted the AS15. There were a couple of pads underneath that were bridged - only visible once the ic was removed. Guess I was sloppy with the solder paste.

Re-doing the ic has cleared the short between Q812 collector and ground, so I guess if I can replace the transistor there's a good chance of getting it working.

So any suggestions how to choose a likely substitute?

Thanks for the help so far budm!

[tn245]

Re: AUO t-con - Help me identify and replace transistor please!

s/c is short-circuit. Sorry, I thought that was a common abbreviation.

So yes, the middle pin to ground is like 0.3 ohms. What does that tell us again?

[budm]

Re: AUO t-con - Help me identify and replace transistor please!

"s/c" What is S/C? The board with burnt transistor, just need to find out if the Output (Collector pin) is feeding into low Ohms/shorted circuit that caused it to burn up.

[tn245]

Re: AUO t-con - Help me identify and replace transistor please!

I would say it probably PNP transistor due to the Emitter is connected to the B+ switching power supply to the right of it, it looks to be some kind of switch for B+. Should check between Collector (middle pin) and ground to see if it shows low Ohms.

Middle pin to ground on this board is showing s/c, but I guess you meant on the board with the good transistor. Sadly I sent that back to get back my £40 refund as it had another fault, so only have the fried transistor and a V0 version board without that transistor here to go on.

Anybody out there have an AUO board with this part on there that can help? Or should I maybe try a PNP in there anyway? Any suggestions on a good choice if so?

I also thought to first re-do the AS15 and try the board with Q812 removed like on the V0 board, just to see if voltages are there and the fuse holds up. Any thoughts?

[budm]

Re: AUO t-con - Help me identify and replace transistor please!

I would say it probably PNP transistor due to the Emitter is connected to the B+ switching power supply to the right of it, it looks to be some kind of switch for B+. Should check between Collector (middle pin) and ground to see if it shows low Ohms.

[selldoor]

Re: AUO t-con - Help me identify and replace transistor please!

sorry just dug up the same thread you found so just deleting the link

[tn245]

I've been waiting ages for a replacement t-con to appear for sale, have so far bought two faulty boards and sent them back. Now I figure I might as well see if I can repair the one I've got - for a fun project if nothing else.

It's an AUO T460HW02 V2. The problem happened when I messed up replacing the AS15 chip, probably introduced a short, and a transistor Q812 went up in smoke. I know there's a good chance other stuff might be dead too, but figure it's worth a try replacing the transitor and re-doing the AS15 and seeing if I can get it going.

The problem is identifying the transistor and choosing a replacement, which I'm hoping you guys might be able to help with.

The part-no is 25727 which I read off one of the boards I sent back (first pic). The same part no was mentioned on a different t-con in this thread (last post):
https://www.badcaps.net/forum/showthread.php?t=24237

Pictures attached. Interestingly the V0 version of this board doesn't have this transistor and associated resistors and caps, and that's the only difference I can see between the versions. The last pic is the same area on the V0 board.

Any ideas what it could be or how to find out?