Reply 20 of 44, by figbash
Deunan wrote on 2021-04-19, 23:53:I think the voltage is OK, it's not uncommon to have it a bit higher to compensate for drop with load and/or stability. So long […]
figbash wrote on 2021-04-19, 18:29:I'm able to get it down to 3.6 (but not 3.3) by messing with the voltage setting jumpers with the CPU removed, though it still doesn't post and the 3.8 is the official jumper layout.
I think the voltage is OK, it's not uncommon to have it a bit higher to compensate for drop with load and/or stability. So long it's not over 4V the CPU will be fine. And it's working at least well enough to show some codes (and reacts to missing memory with C1 error, that also seems correct).
Try lower CPU clock (20/25 MHz) to see if that will make it go any further. Go over all the mobo jumpers (I know, tons of them), especially those that you didn't touch or are not sure what they do - and try to establish what each of them do and if it's set correctly. Perhaps one is missing or something.
And again, these mobos are really quirky about RAM. Most will not tolerate EDO sticks, only FPM ones, and even that is no guarantee. You only need one 72-pin RAM stick to get a 486 mobo to work. See if you have any 4MB sticks, I don't think any of those were EDO, too old for that.
Ok, I tried several different RAM sticks that are all FPM from googling chip numbers and are all different, nothing seems to make a difference there.
I tried 25 and 20 MHz clock but nothing there either.
I went over the jumpers again, as far as I can tell everything is correct. It is very jumper heavy though ha.
Could it be a capacitor issue? Anyone know of a good way to check the capacitors for shorts in circuit? There are 3 tantalum capacitors that seem to read 0 for resistance whereas the others slowly go up.