VOGONS

Acer V65XA - confirming bad SIO

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First post, by kotel

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Hi,

Since I finally found an replacement BIOS for this board (ONLY for testing, the BIOS is from an V65LA), I get the board to finally post 😄
...although the SIO gets scorching hot after 1/2 of a minute to a full minute where the die under the resin is, right after finishing POST...
Measured VCC (5v) and was 4.82v. It stayed like that even after the SIO got scorching hot.
And that's where I get stuck. EEPROM can't be bad, it is from another fully working board.
Another idea would be that the crystal is bad and somehow it speeds up on it's own causing the SIO to get overclocked and overheat, but I don't have any oscilloscopes to test that theory out nor the correct crystal.
Here is the datasheet I found for the FDC37C93x. Might be able to replace it with an FDC37C932 since the datasheet looks to be applicable to the FDC39C93x family. Not sure tho...

Any ideas?

"All my efforts were in vain...
Let that be my disappointment."
-Kotel

Reply 1 of 2, by Horun

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Sounds like either bad chip or its buffer outs are being shorted somehow (just a guess)

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 2 of 2, by kotel

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Horun wrote on 2025-04-27, 22:09:

Sounds like either bad chip or its buffer outs are being shorted somehow (just a guess)

I place my bet on the second case.
As of now, the board "works" with an BIOS from an V65LA, which makes most of the settings inaccessible and makes the PCI slots useless (at least I can't use any of my working PCI GPU's in there), so I am stuck with two ISA slots, one for GPU and the other for a modem or smth....
I also had to physically downclock the SIO (32.754mHz to 27.754mHz crystal) which made the SIO run a little colder, but still out of spec for these SIO's so I had to resort on mounting an PCIe GPU cooler on there and it just works.

Although, measuring the caps near the SIO I found that the ones nearest to the crystal had around 70ohms in circuit, which is too low IMO. Not sure cause I am not a professional, so I ask here if this value is okay

"All my efforts were in vain...
Let that be my disappointment."
-Kotel

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