ASUS A7M266 Kills T-Bred B??

[Stefan Payne]

I got a used A7M266 (1.04)

And tried putting in a T-Bred B from wich I was certain it still worked - and it died.


With some Measurements:
the V-Out of the CPU VRM was around 0,3V - and getting really really hot...
With a TBird it is around 1,85V and works more or less...

I tried setting the Voltage manually, didn't change anything (well, it was ~1,65V without the CPU. And also with the TBird)...

Another Thing: one of the 4V/820uF Caps (those Yellow Fujitsu or so).

What can I do??

[Stefan Payne]

Re: ASUS A7M266 Kills T-Bred B??

I've desoldered those Yellowish Fujitsu Caps (4V/820uF) because one looked odd.
And they measure between 1100 and 1572uF wich seems a bit odd/defective...

[Agent24]

Re: ASUS A7M266 Kills T-Bred B??

Leaky I suppose, if it's measuring high.

[momaka]

Re: ASUS A7M266 Kills T-Bred B??

Interesting problem.

I would say replace those yellow Fujitsu caps if they are measuring high capacitance, as they might be getting leaky, as Agent24 suggested. Furthermore, when I looked for images of the board online, I found this:
https://www.anandtech.com/show/845/3
If you enlarge the picture on that site, you will see that the Fujitsu caps on that board are bulged. Makes me curious if that's due to a board design error or if Fujitsu caps like that are failure-prone (or at least the early ones).

As for replacements, you could probably use regular 6.3V electrolytics if that's all you have (Rubycon ZL or Chemicon KZE minimum). Or go with polymers again.

[Wester547]

Re: ASUS A7M266 Kills T-Bred B??

The early Fujitsu polymers are failure prone. Back in the day, it was initially conjectured that it was because of insufficient rubber seals allowing moisture ingress which resulted in a steady increase in ESR (and eventually, said moisture evaporating to steam). Due to those high capacitance readings, though, it's probably the result of residue from acidic iron compounds that are used as the oxidant for the PEDOT polymerization process. The iron particles remain in the capacitor even after polymerization, which causes leakage current to increase over time (and high leakage current usually means defects in the aluminum oxide).

The specs on those polymers should be about 5040 mA for the allowable ripple current at 105ºC and 12 milliohms for ESR. So, if it's worthwhile to you, polymers are probably the best bet for replacements.

[Stefan Payne]

Re: ASUS A7M266 Kills T-Bred B??

I tried and now it has the same issue (but with 0,8V) with the TBird Chip...

I used two (later 3) Panasonic FR with 2200uF/10V and 470uF/25V Panasonic FM.
Also used 470uF/16V Polymers first.

w/o CPU its 1,7V...

[Agent24]

Re: ASUS A7M266 Kills T-Bred B??

So maybe you have bad VID signal to the VRM controller. I get the impression you are trying to use an unsupported CPU as well?

[Stefan Payne]

Re: ASUS A7M266 Kills T-Bred B??

I can override the VID (and I did), that isn' the Problem.
W/o something in the Socket everything seems fine, though I don't have a Scope.

However when I insert a CPU (even the TBird), the voltage of the VRM is way lower than it should ant it cooks itself.

[Agent24]

Re: ASUS A7M266 Kills T-Bred B??

What cooks itself? The CPU or the VRM?

Maybe you've managed to short both CPUs now or the VRM controller is instead\also damaged.

Did you try the CPU in another board?

[Stefan Payne]

Re: ASUS A7M266 Kills T-Bred B??

What cooks itself? The CPU or the VRM?

VRM of course.

Did you try the CPU in another board?

Only the defective TBred-B.
And it didn't work but voltage seemed fine, if I recall (on an MSI NF2-S Thingy)

[momaka]

Re: ASUS A7M266 Kills T-Bred B??

I guess post some pictures of the VRM area, with the PWM chip and MOSFETs. Older boards like these aren't too complex in terms of VRM design, so we may be able to figure it out. I think it's down either to a bad VRM phase (though probably no bad MOSFETs) or CPU is not getting recognized properly, and either of these could be the reason the low VRM voltage only with the CPU installed (sometimes, the PWM chip datasheet will tell whether or not that is the case).

Also, a dumb question, but since this motherboard appears to use jumper-less settings (V_core voltage and CPU frequency)... have you tried resetting the CMOS as well? Perhaps someone changed the CPU voltage and/or frequency to a value that's causing things to misbehave.

And last but not least, I see this board only supports DDR2100 and DDR1600 RAM as well as what appears to be only early Athlon/Duron chips (so possibly not Athlon XP?... though I doubt it). In any case, it's worth making sure that the RAM and CPU are compatible with the board, just to rule that out.

[Sparkey55]

Re: ASUS A7M266 Kills T-Bred B??

What bios version is installed 1004 or 1007?

[Stefan Payne]

Re: ASUS A7M266 Kills T-Bred B??

I guess post some pictures of the VRM area, with the PWM chip and MOSFETs. Older boards like these aren't too complex in terms of VRM design, so we may be able to figure it out. I think it's down either to a bad VRM phase (though probably no bad MOSFETs) or CPU is not getting recognized properly, and either of these could be the reason the low VRM voltage only with the CPU installed (sometimes, the PWM chip datasheet will tell whether or not that is the case).

Goin to do that next, great Idea, forgot about that.

Also, a dumb question, but since this motherboard appears to use jumper-less settings (V_core voltage and CPU frequency)... have you tried resetting the CMOS as well? Perhaps someone changed the CPU voltage and/or frequency to a value that's causing things to misbehave.

No, it has something we call "Mice Piano" somewhere on the Board, where you can physically set the Voltage and disable Jumper Free Mode.

And last but not least, I see this board only supports DDR2100 and DDR1600 RAM as well as what appears to be only early Athlon/Duron chips (so possibly not Athlon XP?... though I doubt it). In any case, it's worth making sure that the RAM and CPU are compatible with the board, just to rule that out.

Yeah, got the Board to post, then inserted the Athlon XP; saw that the MOSFETs were burnin hot...

[Sparkey55]

Re: ASUS A7M266 Kills T-Bred B??

Goin to do that next, great Idea, forgot about that.


No, it has something we call "Mice Piano" somewhere on the Board, where you can physically set the Voltage and disable Jumper Free Mode.



Yeah, got the Board to post, then inserted the Athlon XP; saw that the MOSFETs were burnin hot...

What model Athlon XP CPU did you install?
What BIOS version installed?

[Sparkey55]

Re: ASUS A7M266 Kills T-Bred B??

Bump.

[Stefan Payne]

Re: ASUS A7M266 Kills T-Bred B??

What model Athlon XP CPU did you install?
What BIOS version installed?

T-Bred B, don't remember the exact model.

BIOS was the latest you could download from the ASUS Site.

[Sparkey55]

Re: ASUS A7M266 Kills T-Bred B??

In post #1 did you update the bios BEFORE putting in the T-bred Athlon XP cpu?
I have read elsewhere that someone did that and the cpu fried because the vrm did not have the correct VID programmed into the bios

Also inserting a cpu into a powered up board is a good way to destroy them both.

[Sparkey55]

Re: ASUS A7M266 Kills T-Bred B??

Asus changed the vrm design starting with PCB rev. 1.05 and above.
You state that you have rev. 1.04
That may be part of the problem.

[brethin]

Re: ASUS A7M266 Kills T-Bred B??

That board doesn't support Thoroughbred CPUs,.

https://www.asus.com/us/supportonly/.../HelpDesk_CPU/

[brethin]

Re: ASUS A7M266 Kills T-Bred B??

A7M266-D does support Thoroughbred CPUs

https://www.asus.com/tw/support/cpu_support