First post, by feipoa
- Rank
- l33t++
I have a Biostar MB-8433UUD v3.1 motherboard which I am trying to fix the on-board floppy and serial controllers. I first thought the issue was the SuperI/O circuit that went bad. It has part number UM8663BF. I replaced it, but I still cannot access my floppy disk. I then thought maybe some of the DIP IC's might be bad (74LS14Nx1, 74F244PCx2, 74LS245Nx2, 74F08Nx1, UM9515-01), so I desoldered all of them, put in DIP sockets, and replace them with new chips. Still cannot access the floppy disk. I then recapped all the electrolytic capacitors (9x10uF, 2x47uF, 4x100uF) - still no floppy disk access.
The serial ports also don't work, which is curious, because the serial port IC is a seperate chip, UM8667. I didn't bother to replace this because I think whatever is causing the floppy controller not to work is likely the same thing which is affecting the serial IC.
If I use an ISA I/O card with an onboard floppy controller (UM8663AF), floppy access works fine as long as I leave "onboard FDC" enabled in the BIOS and set A to 1.44 MB 3.25" drive. So I know the issue is not with the floppy drive or cable. I suspect the issue may be with a certain section of the Southbridge (UM8886BF) IC. I say a "certain section" because the PS/2 mouse port, which is connected to the Southbridge, still works. Alternately, there may be some bad SMD resistors or capacitors, or a bad SIP resistor pack (sometimes called a "resistor network").
Has anyone had an SMD capacitor or resistor go bad? If so, how did you narrow down the failure?
This motherboard used to function as a server many years back and I specifically recall the on-board floppy working. After an uptime of approx. 5 months, the computer crashed, and which point the floppy drive stopped working entirely. If I used an ISA I/O card, everything works fine, however I'd still like to fix the on-board features.
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