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

[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?

[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

[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.

[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!

"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!

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?

[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!

[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!

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?

[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!

[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.

[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.

[tom66]

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

If AVDD = VIN (more or less) the circuit is not switching. AVDD should be around 15V and this boost converter is then used to generate VGH and VGL.

[tn245]

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

Thanks T30M1. Q302 seems a little larger than the SSM6J212FE. It's just under 3mm long while the SSM6J212FE is 1.6mm. See attached.

lookimback, thanks for the tips. It is helpful. This was the first AS15 I did. I've since done others that have gone much better and worked first time. Replacing my worn out soldering iron tip helped a lot, but so did some of the techniques you mentioned. Getting better all the time.

tom66. Thanks! And Q302 being short would cause that right? Would you go along with it being a P-channel mosfet in this application?

[tom66]

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

No, I think you have other faults on the board, with that transistor out you should still have 15V AVDD and a distorted image on screen.

[tn245]

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

Ah, ok then, thanks. Which part of the circuit should I be looking at?

Just checking though.. you followed that we're talking about a different component than the transistor at the start of the thread? The six-pin mosfet connected pretty much directly to Vin. From my very limited understanding of the circuit I figured it would be pretty critical.

[tn245]

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

Well, I'm a bit lost now. Can you give me some pointers tom66 or others?

Tom, I figure you're talking about the boost converter around the inductor L812 (6R8). I'm not sure how to figure out what's going wrong with it though. There are all kinds of voltages missing around the board. The only suspect component I can find is that Q302 MOSFET.

Some more voltages, compared with readings from the good board:

            Good Board       Bad Board
GAVCC1 	        3.3 	        0
LVDS_OUT        3 	        0
V3D3 	        3.3 	        0
V2D5 	        2.4 	        0
Q811 (RSS065N03)
S, G, D         0, 0.7, 11.7 	    0, 0, 12
U802 Pins 1, 2, 3 	3.2, 0, 2.4 	    0, 0, 0
U804 Pins 1, 2, 3 	0, 1.7, 3.2 	    0, 0, 0

Any thoughts? Any more readings I could take to narrow things down?

[T30M31]

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

TN245, it looks like a P-channel MOSFET would work as a high side switch the way Q302 is connected on this board. Q302 appears to be in an SOT26 case and I have found 2 possible replacements. Links to both are include below and you can check physical dimensions using the data sheets provided on the Farnell website.

I don't know if Q302 is related to the missing voltages you referred to in your last post but the difference in resistance between Q302 pins 3 and 4 for the good and bad boards does indicate a problem around Q302. The lower resistance could be due to R330 or C307 but I think Q302 is most likely the problem.

http://uk.farnell.com/diodes-inc/dmp...t26/dp/2061420

http://uk.farnell.com/taiwan-semicon...t26/dp/1864596

[tn245]

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

Awesome T30M31! Thanks so much for taking the time to look those up. I found someone selling the DMP3056LDM on ebay for £1.57 free postage, so not much to lose there if it doesn't work. Have ordered one.

Still very interested in others' opinions about the other missing voltages and if it's related to Q302 or something else.

[tom66]

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

I'd check D812 isn't short, yes, I think that's the converter.