Gregory's Serversomeone's been hacking on the card, adding this bodge wire. it bridges 5V over to two pins on the CPU socket (AN1 and AN3) presumably to support a faster Pentium Overdrive.
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 whoever did the bodge wire also replaced the clock oscillator, changing from 60MHz to 66MHz. there's also some corroded vias. oh yeah and i think someone exposed this board to a lot of heat since the label on the flash memory chip has bubbled up like a matzah. anyway, i've plugged in a Pentium 90. it should be fine at 99MHz. i don't have the right heat sink so i bent up a section of music wire to hold this junk box heat sink in place. will it work? all right, i'm very suspicious of the soldering job on this clock oscillator. the upper right pin is the oscillator output and it looks like it may not be connected. boom! that did the trick! except now the floppy drive isn't working so i can't put in the reference disk 🙃 floppy drive issue seems to be this leaky electrolytic capacitor. it was working before, so i guess it must have been slowly degrading. ugh. i have this same issue with another Type 4 complex I have (486DX2-66). this is probably logic analyzer time now :blobsweats:  @tubetime logic analyser time is always a good time! 😅 Best of luck, tho! <3 the floppy controller chip (upper left) doesn't natively support MCA bus, so the chip in the middle (U26) implements that for it. Specifically, U26 uses an external open-drain buffer (U37, bottom) to drive the ARB lines. but it *senses* those same ARB lines with 4 separate pins. [most likely U26 is a semicustom gate array with a limited number of possible open-drain outputs] my theory is that for some reason, U26 (85F0464) isn't working correctly and is driving 0 onto the arbitration bus when it means to drive 2. so it thinks that it has lost arbitration, but it actually won it. then it hangs in a halfway state, and the DMA controller throws the timeout error (presumably by asserting NMI). @tubetime always felt weird that even on IBM hardware that supports it, that OS/2 cant do an ACPI soft shutdown. Even OS/2 4.52  @tubetime Half a warped OS... The whole IBM fumbling the Star Trek thing with OS/2 and the Warp name silliness was pretty amusing. @tubetime I like that as a concept. Simple and elegant without any state machine complexity. |
sus.