Ujeen wrote on 2024-11-12, 01:01:

any luck with your issue ? (I'm burning processors here occasionally 😀 , so quite curious what it is in your case)

What I can say is that CPU was still alive when used on my replacement board... Now another Vogons user has that board and will try to fix it (3rd vogons user that has that board).

ah ok , got it

Linoleum wrote on 2024-11-12, 01:27:

What I can say is that CPU was still alive when used on my replacement board... Now another Vogons user has that board and will try to fix it (3rd vogons that has that board).

Don't mean to be too nosy here, but OK to tell who it is or if they have a thread for it? I'm just curious to see the outcome of that board. Perhaps we should just keep kicking around this board among us until someone fixes it. 😁

Reading back on this thread, I agree with razs_pl's suggestion that a trace could have burned out somewhere. If nothing looks bad on both sides of the board, it could be a trace on one of the inner layers. Now that could make tracing the issue much harder... though not impossible. On some boards, you can see inner layers under very strong light on the other side of the board. With that and some voltage measurements at the power pins of various ICs, it may just reveal what the issue is.

As for the CPU header not working...
On some old motherboards, the CPU fan is enabled (On or Off) through a BJT transistor. It could be that this transistor has burned (open-circuit is not uncommon for smaller BJTs)... or it could be that it's not getting its Base voltage due to whatever circuit that is driving it is not working or itself not getting an enable signal.
Again, my first step would be to trace all of the power pins on all of the ICs to see if they are getting proper power.

Anyways, I suppose it's moot to further discuss it at this point, now that you have moved on. Though again, would be great to know who's troubleshooting it and hopefully they'll be posting a thread / continuation on the progress to see what happened to this board.

I can confirm I am now the proud recipient of this cursed motherboard. 😁

I just got it today, so I haven't really had time to dive into inspecting it yet. I did quickly check of the CPU fan pins, since that was mentioned as not working. It appears the tach pin is shorted to ground. So possibly whatever burned out might have shorted the tach on the CPU fan. The tach pin on the other fan header seems fine.

It might take me awhile to dive into this board, since I'm currently working on diagnosing some other motherboards. This stuff gets time consuming. But if and when I do find anything, I'll keep folks updated here. 😀

Awesome, keep us updated how it goes. 😀

Shorted tacho pin could be either due to a shorted ceramic noise filter cap somewhere on that line... or as bad as a burned out LPC/superIO chip, which would be a bummer, obviously. I'm more inclined to think it's the former, since the other fan appears fine and especially if the LPC/SIO is not overheating. Also, IIRC, some early boards will refuse to POST if they don't detect a tachometer signal for the CPU fan - that was so that if a CPU fan was not installed, the board would halt and not boot. But I don't think most Slot 1 boards were like that though. I think only some AMD boards did this, starting around the Athlon era (not sure if slot A or s462.)

P2B monitors FANs thru small winbond chip, possibly W83781D, which is weird for ASUS considering their own "asic" AS99127F has build in Tacho reading. P2B-VT doesnt have W83781D onboard so maybe here its measured by AS99127F. Bad news is Tacho pin goes straight to monitoring chip (with 10K pullup to 5V) with no buffering so you might have dead/internally shorted ASUS chip.

I guess there is no pinout / datasheet available for the AS99127F chip? I tried doing a quick search but couldn't find anything.

edited: Meant AS97127F, since that's the chip on the board.

https://theretroweb.com/chips/4546#docs

rasz_pl wrote on 2024-11-14, 18:34:

https://theretroweb.com/chips/4546#docs

Thank you! 😀

edited:

I realize why I couldn't find it. The chip on the board is an AS97127F, where as the above link is AS99127F.

Not sure if there are any differences between the respective chips?

ah you are totally right! and AS97127F pinout doesnt match AS99127F when comparing against P2B 1.12 boardview 🙁 not even VCC/ground match
I have a collection of ASUS ASIC datasheets and AS97127F is not in there.

At least confirming that they don't have the same pinouts is useful information. Saves me from misinterpreting any probing of that chip.

So either AS97127F never had any fan monitoring, or implementation was broken forcing ASUS to use W83781D on P2Bs.
Maybe OEM P2B-VE dont monitor tacho at all, still weird for the pin to just be shorted.

I don't really do soldering or similar work on but two of the capacitors look odd to me. The purple one on bottom looks like it has corrosion on top, and then the one by the fan header on left - doesnt exactly look corroded but maybe rough? Its definately not K stamped like the others.

This is going to be anti-climatic, but the board appears to be working.

The fan thing was a red herring. I realized when I looked at the board again tonight, that I had mixed up the fan headers. They are labelled a little weird, since what should the CPU fan is actually labelled SYS_FAN. I saw that label and assumed the other fan header was the CPU fan header. However, it's labelled PS_FAN. It was the PS_FAN header I had measured the grounded tach signal.

I gave the board a detailed inspection under the microscope. Since OP had mentioned a burning smell, I assumed that maybe something had blown and it should be visible somewhere on the board. However, the only issue I could find was a via near the Southbridge chip had some corrosion in it. It looks like the coating had somehow rubbed off exposing the raw copper. This was such a small thing, it was only visible under the microscope.

After that, I decided to do a power test. I checked basic voltages and they all seemed normal (including the fans). I then plugged a fan into each of the fan headers and they both spun up just fine.

At that point, I added a Pentium II 400 and a POST card. That seemed fine; I was getting POST numbers. Then I added RAM and a video card, and the system booted right up.

The only other issue (the error on the boot screen) is the CMOS battery was low. It tested at only 2.7V, so I replaced it.

I booted into DOS and did some basic testing, running various benchmarks. Everything worked as normal.

I haven't stress tested it yet, tried the built-in video, or tested all the expansion slots. It's possible there still could be issues. But on first pass, the board appears functional.

BinaryDemon wrote on 2024-11-15, 18:11:

I don't really do soldering or similar work on but two of the capacitors look odd to me. The purple one on bottom looks like it has corrosion on top, and then the one by the fan header on left - doesnt exactly look corroded but maybe rough? Its definately not K stamped like the others.

Caps are perfect. I inspected them close up and there is no visible issues. Usually bulging, leaking or corroded caps will be pretty obvious.

Did some more testing of the motherboard.

I switched to the built-in ATI Rage 3D video chip and that seems to be working fine. I tried the POST card in all the PCI slots and no abnormal results there.

I further installed an SB16 sound card and tried some games under DOS. Everything worked fine.

Between testing games and more benchmarking, I probably ran this board for 30-45 minutes. No crashes, lockups or signs of overheating issues.

I re-ran Speedsys since in the first benchmark there were some funny dips on a few of the tests. But this time the bar graphs were perfectly smooth.

For that one corroded via, I cleaned it out as best I could and applied some thin solder mask to protect the copper. It dried transparent so it's barely noticeable.

I don't think that via would have been an issue, since the corrosion seemed to be a surface issue as a result of the exposed copper. I am confused as to how it was exposed in the first place, since there are no other scratches or damage around it.

Insofar as the symptoms the OP was reporting, I'm a bit stumped. Because the board itself is working, I'm assuming the issues were elsewhere. Since the OP reported the board stopping at a memory related POST code, maybe there was an issue with a DIMM? Even just dirty contacts? I gave the memory slots a spray with some Deoxit for good measure, but they seemed fine to me.

I wonder if the low CMOS battery might have caused some issues? Although it should have still allowed the board to boot.

As for the burning smell, since the OP mentioned a fan not spinning, possibly the fan itself burnt out? I've had that happen before and that can result in a burning odor.

Other than that, the board appears fully working and in great shape.

Heck yeah! I was on the edge of my seat watching this board getting handled. Awesome to see it working just fine. Now I'll forever (maybe) be stuck wondering: What happened? Good stuff

Major Jackyl wrote on 2024-11-16, 17:58:

Heck yeah! I was on the edge of my seat watching this board getting handled. Awesome to see it working just fine. Now I'll forever (maybe) be stuck wondering: What happened? Good stuff

Thank you! I suppose we'll never truly know what happened, but at least we know it probably wasn't the motherboard. 😁

There was a time when I smelled a burning electronics smell coming from the PC I had built for my mother. It was working fine, and I couldn't isolate the source of the smell. Maybe six to nine months after I had visited her and first noticed it, her PC stopped powering on. It turned out that the mediocre power supply had a loose fitting power cord, and the resistance eventually cooked the power cord's contact. Fortunately, I had come prepared with a spare power supply just in case. I later used a dead power supply to scavenge a socket, and used it for repair and the power supply worked fine.

OP here... The previous owner jerry-rigged a P3 fan on top of the P2 CPU... It blew up and probably killed the tach pin on the edge of the board in the process. I replaced it with a 2 pin fan just for the tests... So the board was most probably waiting for a tach signal.

The lesson here fellow kids, is to be very thorough with your diagnostics.