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Motherboard repair

M

Mr. Land

Jan 1, 1970
0
Hi,

I have an old AOpen AX6BC motherboard I've been running in a server for
a while. The other night it blew out. There was a distinct burning
electronic smell.

After taking it out of the system and giving it a close inspection, I
found one of the small surface mount transistors had burned out
(charred, case cracked.)

While I know there's a very good chance something else is wrong, I
still think it's worth replacing that blown transistor to see if that
fixes it before I toss the board in the trash.

Problem is, I can't seem to find a replacement. The package is a small
rectangle with 3 leads on one side and the collector plate on the
other. I believe the case type is "SOT 89" There are only 4
alphanumerics printed on the case, oriented as follows:

+---+
|D K|
| |
|0 J|
+---+


....any chance someone could help me find a substitute?

Thanks.
 
J

James Sweet

Jan 1, 1970
0
Mr. Land said:
Hi,

I have an old AOpen AX6BC motherboard I've been running in a server for
a while. The other night it blew out. There was a distinct burning
electronic smell.

After taking it out of the system and giving it a close inspection, I
found one of the small surface mount transistors had burned out
(charred, case cracked.)

While I know there's a very good chance something else is wrong, I
still think it's worth replacing that blown transistor to see if that
fixes it before I toss the board in the trash.

Problem is, I can't seem to find a replacement. The package is a small
rectangle with 3 leads on one side and the collector plate on the
other. I believe the case type is "SOT 89" There are only 4
alphanumerics printed on the case, oriented as follows:

+---+
|D K|
| |
|0 J|
+---+


...any chance someone could help me find a substitute?

Thanks.

Chances are it's an N-channel power MOSFET, look for the regulator
controller chip nearby and look up an app note, it should have a reference
design with suitable mosfets.
 
R

Rifleman

Jan 1, 1970
0
James Sweet said:
Chances are it's an N-channel power MOSFET, look for the regulator
controller chip nearby and look up an app note, it should have a reference
design with suitable mosfets.


It seems that the AX6BC is equipped with smt mosfet and the AX6B with
ordinary hole mounted with heatsinks. On mine AX6B one of the mosfet
transistors were burned but those were CEP6030L with TO220 package but for
AX6BC I think they use D2-pak. Replaced it with another CEP6030L and it is
still running.
RC5051 is used as programmable synchronous buck controller. You might be
able to check the drive to those two mosfet transistors. Download the
application note AN-53
http://www.fairchildsemi.com/an/AN/AN-53.pdf
interesting reading.


Bjorn
 
F

Franc Zabkar

Jan 1, 1970
0
Hi,

I have an old AOpen AX6BC motherboard I've been running in a server for
a while. The other night it blew out. There was a distinct burning
electronic smell.

After taking it out of the system and giving it a close inspection, I
found one of the small surface mount transistors had burned out
(charred, case cracked.)

While I know there's a very good chance something else is wrong, I
still think it's worth replacing that blown transistor to see if that
fixes it before I toss the board in the trash.

Problem is, I can't seem to find a replacement. The package is a small
rectangle with 3 leads on one side and the collector plate on the
other. I believe the case type is "SOT 89" There are only 4
alphanumerics printed on the case, oriented as follows:

+---+
|D K|
| |
|0 J|
+---+


...any chance someone could help me find a substitute?

Thanks.

Can you locate the part in this photo?
http://global.aopen.com.tw//Products/images/MB/products/ax6bc-b.jpg

Is it in the top LH corner? If so, then check the nearby capacitors
for signs of leakage or swelling. What is the part number and logo on
the IC to the left of the lower 4 caps?


- Franc Zabkar
 
Mr. Land said:
Hi,

I have an old AOpen AX6BC motherboard I've been running in a server for
a while. The other night it blew out. There was a distinct burning
electronic smell.

After taking it out of the system and giving it a close inspection, I
found one of the small surface mount transistors had burned out
(charred, case cracked.)

While I know there's a very good chance something else is wrong, I
still think it's worth replacing that blown transistor to see if that
fixes it before I toss the board in the trash.

Problem is, I can't seem to find a replacement. The package is a small
rectangle with 3 leads on one side and the collector plate on the
other. I believe the case type is "SOT 89" There are only 4
alphanumerics printed on the case, oriented as follows:

+---+
|D K|
| |
|0 J|
+---+


...any chance someone could help me find a substitute?

Thanks.
You can buy a complete board on eBay for $15. How much is this worth to
repair? I know, it is the principle of the thing but your time has
value too.
GG
 
J

James Sweet

Jan 1, 1970
0
You can buy a complete board on eBay for $15. How much is this worth to
repair? I know, it is the principle of the thing but your time has
value too.
GG

What about the educational value and the satisfaction of repairing
something? As others have pointed out in the past, this isn't
sci.electronics.replace.
 
I've been getting satisfaction for many years repairing.electronics.
Also, have done some design as well but when you're talking $15 to
replace something or spend several hours working on multi-layer boards
that may have internal burned traces and other bad components AND no
prints, why bother? My time is worth more than $7.50 an hour. I assume
yours is as well. Its not like you're restoring a collectible item that
merits the TLC. I'm done
GG
 
M

Mr. Land

Jan 1, 1970
0
Hi,

Thank you very much for your response. Unfortunately, even though I've
dabbled in electronics in the past, this is sounding like I'm in a bit
over my head...I don't even know what "look up an app note" refers to.

But thanks for trying to help me.

Cheers.
 
M

Mr. Land

Jan 1, 1970
0
I went to read your reference...hmm, looks good, but way over my
head!!!!

I did manage to notice in their sample circuit the two mosfets in
series, and since as I stated originally there is a second device
(which is OK visually, at least) with the same part number, this might
indeed be close to what I have.

FWIW, since I had nothing to lose, I took a wild (in retrospect) guess
that it might be an NPN transistor and tack-soldered one I had lying
around. The BIOS booted! But as soon as it tries to read from the
boot drive, it either states there's a missing file, or it can't read
it at all. So I guess the NPN was a bad guess!

Also in retrospect I'm pretty lucky I didn't blow the whole thing up!!!

Thanks a lot for your help!!!
 
M

Mr. Land

Jan 1, 1970
0
Actually, thanks, I did indeed acquire a replacement on eBay.

But when I look at that board, all the parts on it, it just seemed like
such a waste to just toss it.

Thank you for your reply.
 
M

Mr. Land

Jan 1, 1970
0
Yes, I can see it! This is cool!

I had to load your picture into a graphics editor and zoom in a bit.
But here's where the failed part is: to the right of the PCI sockets
there is one large, square IC that appears to have some kind of
orange-colored mark on its upper left hand corner. If you sight along
the top edge of that IC, and move your gaze directly right, you'll come
to 2 electrolytic capacitors standing next to each other; just below
those capacitors is a row of small surface mount components, some
caps, some resistors I think. If you sight along this row and continue
moving your eyes to the right, you'll come to a white dot. That is the
metal (heat sink?) tab of the device that blew out. The body of the
device is above that, and the 3 connection leads are just above that.
If you go back to the 2 electrolytic capacitors, and look directly
above the left one, you'll see the other device that matches the one
that burned up.

Hey, thanks so much for taking the time to post this picture!!
 
J

James Sweet

Jan 1, 1970
0
Mr. Land said:
I went to read your reference...hmm, looks good, but way over my
head!!!!

I did manage to notice in their sample circuit the two mosfets in
series, and since as I stated originally there is a second device
(which is OK visually, at least) with the same part number, this might
indeed be close to what I have.

FWIW, since I had nothing to lose, I took a wild (in retrospect) guess
that it might be an NPN transistor and tack-soldered one I had lying
around. The BIOS booted! But as soon as it tries to read from the
boot drive, it either states there's a missing file, or it can't read
it at all. So I guess the NPN was a bad guess!

Also in retrospect I'm pretty lucky I didn't blow the whole thing up!!!

Thanks a lot for your help!!!

If you got that close then it's almost certain that replacing that one
component will fix it. Try an N-channel mosfet.
 
M

Mr. Land

Jan 1, 1970
0
I can't explain or justify my desire to fix this board.

All I can say is that when I go to drop it in the trash barrel, I look
at all the components on it and the work that went into making it (ok,
well, my board and 99,999 others just like it) and I think that I may
be chucking it all because of 1 little component, I can't bring myself
to do it.

You're right, I guess that's pretty silly. But I also think that if I
manage to fix it, I'll feel good about accomplishing that, even if the
$$$ doesn't weigh out.

Thank you for taking the time to reply.
 
M

Mr. Land

Jan 1, 1970
0
Where would an ordinary person like myself acquire one of these
CEP6030L's in the D2 package?

Thank you!
 
J

James Sweet

Jan 1, 1970
0
Mr. Land said:
Where would an ordinary person like myself acquire one of these
CEP6030L's in the D2 package?

Thank you!

FDP6030L from www.digikey.com should do the trick for you, might even be
able to get a free sample from Fairchild.
 
F

Franc Zabkar

Jan 1, 1970
0
I had to load your picture into a graphics editor and zoom in a bit.
But here's where the failed part is: to the right of the PCI sockets
there is one large, square IC that appears to have some kind of
orange-colored mark on its upper left hand corner. If you sight along
the top edge of that IC, and move your gaze directly right, you'll come
to 2 electrolytic capacitors standing next to each other; just below
those capacitors is a row of small surface mount components, some
caps, some resistors I think. If you sight along this row and continue
moving your eyes to the right, you'll come to a white dot. That is the
metal (heat sink?) tab of the device that blew out. The body of the
device is above that, and the 3 connection leads are just above that.
If you go back to the 2 electrolytic capacitors, and look directly
above the left one, you'll see the other device that matches the one
that burned up.

The advice you've received so far is for the MOSFETs to the left of
the CPU slot. Clearly you have some other fault near the southbridge.
Does your component have a circuit reference, eg Qnn (transistor nn)
or Dnn (diode nn)? Judging by the copper tracks, it appears that your
transistor (?) is driven by the IC below the second capacitor. If I'm
right, and if you can identify this IC, then its application circuit
may reveal the function of the transistor.


- Franc Zabkar
 
M

Mr. Land

Jan 1, 1970
0
Yes, there is a Qnn number near the blown component. Unfortunately,
right now I'm at work, and the board is home, but I will post that
number later tonight.

Also, yes, while I was tacking in the NPN xstr, I did notice that the
foil trace for (what I thought was) the base lead went down to the
small IC below and to the left. That IC is an LM324 (I remember it
because I recognized the number.)

Thanks again, folks!
 
M

Mr. Land

Jan 1, 1970
0
Thanks. Looks like the FDP6030L is a TO-220 package, while the
FDB6030L seems to be the smaller "D" package which I believe was on the
board originally.

Unfortunately, it seems the minimum quantity for the FDP part is 45,
for a total of just under $40. Think I'm heading for a dead end...

Thank you.
 
M

Mr. Land

Jan 1, 1970
0
Spoke too soon, found one at Mouser (in the right package) for $1.50.
Thanks!
 
F

Franc Zabkar

Jan 1, 1970
0
Yes, there is a Qnn number near the blown component. Unfortunately,
right now I'm at work, and the board is home, but I will post that
number later tonight.

The "nn" is not important, it's the "Q" that tells us that the
component is indeed a transistor of some kind. A "diode test" of the
good part using your DMM should identify whether this is a BJT or a
MOSFET.
Also, yes, while I was tacking in the NPN xstr, I did notice that the
foil trace for (what I thought was) the base lead went down to the
small IC below and to the left. That IC is an LM324 (I remember it
because I recognized the number.)

An LM324 is a quad opamp. I have no idea what its function would be on
this board. OTOH, an LM3524, a PWM regulator, might make sense if
there was a coil nearby, but I don't see any.
Thanks again, folks!


- Franc Zabkar
 
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