Recapped, now burning smell!! Need Guru!!

[glutton4punishment]

Received a MB with 12 bad caps, all 820uf, 6.3v. The caps available to me were 1000uf, 6.3v. According to google search, that shouldn't have been a problem.

It was a long royal pain in the ass to switch out the caps, but I got it done...not pretty soldering, but it's done!


Started it up and to my utter astonishment, it worked!

BUT....a overheating smell. I shut her down, and found out the culprit

On the pic, transistor (?) # 1 is burning hot to the touch. #2 is hot, but not terrible. #3 and #4 are cool to the touch, as are the other transistors on the MB. BTW, the new caps are the black ones in the pic, and a lot of them are located physically next to the transistors.

What should I do?
What did I do wrong?
Would the MB work if I didn't solder a cap on right?
Is it the 1000uf vs. the 820uf values (shouldn't be...and please don't make me change them out!!)

thanks a million!

[stj]

Re: Recapped, now burning smell!! Need Guru!!

what make and series are the new caps?

[Heihachi_73]

Re: Recapped, now burning smell!! Need Guru!!

I see NCC, Nichicon and Sanyo caps... I'd be more interested in finding out what the old caps were before determining the series.

Those transistors were probably already fried by the ripple current caused by the twelve bad capacitors. If the PC still POSTed with two failed transistors, it most likely did with the bad caps intact too, just rebooting or freezing all the time. Of course, disregard this if they were still cool before replacing the caps; I can't see how 1000uF in place of 820uF could cause the start of a smoke show though, unless the ESR was way different (however, the ESR would have been through the roof with the failed caps). Nothing worse than swapping in new parts only to see them release the magic smoke seconds later (SMT transistors like those are also an absolute PITA to remove, but it looks like it will have to be done to make that board happy again).

[glutton4punishment]

Re: Recapped, now burning smell!! Need Guru!!

Thanks for the responses!

The new caps are Nichichon.
The old cap were TK.
What's interesting is that the whole board was populated with the TK caps... ALL of the 820uf caps blew, but the rest are good. I figured it was a bad run for that value. -


I have no idea if the MB worked before I got it, or if the transistors were cooler than now.

Nothing worse than swapping in new parts only to see them release the magic smoke seconds later

I wasn't clear enough in my description. No smoke, just a burning smell. I immediately turned it off b/c after all that work, I didn't want to fry the board. I can see that the really hot transistor is starting to discolor the MB from green to brown on the side opposite the transistor, and if you look closely in the pic, the "glue" from the transistor to the plate of metal under it is turning brown.


Right now I can get the computer to boot to windows and I've let it run for about 5 minutes before getting nervous and shutting it down again.

Some questions:
1. If I had screwed up one of the soldering of even one cap, would the computer still turn on?
2. Is the transistor(s) running hot b/c of my lousy job of cap replacement, or something else going on?
3. Since everything is working, should I try to ghetto rig a heat sink for the hot transistor, does it need to be replaced, or what??

[stj]

Re: Recapped, now burning smell!! Need Guru!!

i'll ask again,
what series of nichicon,
and what series of Tk

[ben7]

Re: Recapped, now burning smell!! Need Guru!!

I have no idea if the MB worked before I got it, or if the transistors were cooler than now.

Ding Ding Ding.
It very well could have been faulty from the beginning. Countless cases where faulty capacitors have caused inductors to overheat, and other bad stuff to happen.

Test in using your meter.
Check to see if it is shorted. If it seems partially shorted, either remove the CPU or desolder the transistor and then test it.

-Ben

[glutton4punishment]

Re: Recapped, now burning smell!! Need Guru!!

i'll ask again,
what series of nichicon,
and what series of Tk

Since I don't know how to answer this, I'll just give your all the numbers:

TK ATWY 909B
Nichichon AD621 PET

hope this is what you're asking for!

[ben7]

Re: Recapped, now burning smell!! Need Guru!!

Since I don't know how to answer this, I'll just give your all the numbers:

TK ATWY 909B
Nichichon AD621 PET

hope this is what you're asking for!

You've gotten the TK caps right, there is an ATWY series.
On the nichicon caps, you have the date code and I think PET is the plastic the sleeve is made out of.
On the nichicon caps, the series is printed right "under" the negative stripe. It might say something to the effect of "HM(M)" or "HD(M)".

-Ben

[stj]

Re: Recapped, now burning smell!! Need Guru!!

datasheet

[glutton4punishment]

Re: Recapped, now burning smell!! Need Guru!!

Ding Ding Ding.
It very well could have been faulty from the beginning. Countless cases where faulty capacitors have caused inductors to overheat, and other bad stuff to happen.

Test in using your meter.
Check to see if it is shorted. If it seems partially shorted, either remove the CPU or desolder the transistor and then test it.

-Ben

This is not easy for me. There are two transistors with the same ID #'s on them, numbers 1 & 2 on the picture. Remember #1 is extremely hot.

So lets pretend that the legs sticking out of the bottom of the transistors are lableled ABC from left to right. Leg B is cut off, leaving only A and B soldered to the MB.

With DMM on diode mode, for transitor #1 I get:

With Red lead on leg A, Red lead on B, Red lead on C
Black lead on leg A-- NA , 0, .90
Black lead on leg B-- 0 ,NA, .50
Black lead on leg C-- .90, .60,NA

This is getting frustrating!

[glutton4punishment]

Re: Recapped, now burning smell!! Need Guru!!

You've gotten the TK caps right, there is an ATWY series.
On the nichicon caps, you have the date code and I think PET is the plastic the sleeve is made out of.
On the nichicon caps, the series is printed right "under" the negative stripe. It might say something to the effect of "HM(M)" or "HD(M)".

-Ben

my bad! the nichichon is HM(M)

[ben7]

Re: Recapped, now burning smell!! Need Guru!!

my bad! the nichichon is HM(M)

Yes HM series is good for motherboard use.

This is not easy for me. There are two transistors with the same ID #'s on them, numbers 1 & 2 on the picture. Remember #1 is extremely hot.

So lets pretend that the legs sticking out of the bottom of the transistors are lableled ABC from left to right. Leg B is cut off, leaving only A and B soldered to the MB.

With DMM on diode mode, for transitor #1 I get:

With Red lead on leg A, Red lead on B, Red lead on C
Black lead on leg A-- NA , 0, .90
Black lead on leg B-- 0 ,NA, .50
Black lead on leg C-- .90, .60,NA

This is getting frustrating!

Hm, seems like the gate is shorted to the drain (bins A and B, FYI B is also connected internally to the thermal tab). Remove the transistor and test it again, just to make sure it is actually the problem and not something else. Also FYI, the transistor is a MOSFET, not an BJT, so don't expect to get diode junction readings unless the FET is turned on or you are measuring the internal reverse protection diode. If you are confused, look up how to test a FET with a DMM.

-Ben

[glutton4punishment]

Re: Recapped, now burning smell!! Need Guru!!

thanks, Ben, glad you were able to understand my post. Well, I'm off to desolder the MF!