naujoks wrote on 2024-09-07, 15:14:

I didn't discover any broken off parts, loose legs on the ICs or broken traces. I tried different VLB slots.

Any ideas what else I could try?

There are two different pinouts for the serial port connection cable. Maybe you are using the wrong kind of cable. Quick check: If you use the right kind of cable, pin 5 at the serial port is connected to ground of the PC.

I'm assuming that the built in serial port, visible on the top right, is the one that came originally with this card (it is presently connected to COM1).
I have also tried to connect it to the COM2 header on the board as well as the cable connected to a serial port in an external bracket.

naujoks wrote on 2024-09-07, 16:43:

I'm assuming that the built in serial port, visible on the top right, is the one that came originally with this card (it is presently connected to COM1).

Of course, you are right. I missed that there is a COM port on the bracket of that card, because I just saw the two 10-pin headers next to each other, but missed that one of them is the game port. Another common cause of mouse problems is missing +12V or -12V supply, but this would affect ISA cards as well as VLB cards. Actually, everything except IDE is connected to the ISA bus on VL I/O controllers, so the serial ports are supposed to behave exactly as they would on an ISA card.

Does your BIOS recognize the COM ports on the VLB card? This would show that the serial ports are at least enabled and the processor interface to them works properly.

Do the COM ports (3F8, 2F8) show up in the boot screen after POST?

You can test the serial ports with CheckIt. Normally it requires a loopback adapter, but even without it you can run a basic test to check if the computer is communicating with the ports.

Yes they're showing up on the boot screen.

This means the 8663 chip is interfacing correctly to the processor. If serial ports fail, there are different possiblities. CheckIt might help to distinguish those:

• No clock to the 8663, because something is wrong with the 24.000MHz crystal or the traces to it. In that case, the floppy interface will fail as well, as both the serial ports and the floppy controller are clocked from this source. Checkit will diagnose missing clocks at least in the internal loopback test, maybe even earlier.
• Some more subtle failure inside the 8663 chip. CheckIt will likely fail in this case.
• Failure of the 8667 chip, or no sufficient power supply to it. You expect around -11V at the "top" end (next to the electrolytics caps) of D1, and +11V at the "bottom" end (closer to the ISA slot) of D2.
• Failed cable/socket on the card, and the external bracket you used is made for the other pinout.

If the tests in CheckIt pass (except for the external loopback test), you can be quite confident that the 8663 chip is working fine and the jumpering is OK.

Where can I find CheckIt?

naujoks wrote on 2024-09-07, 18:50:

Where can I find CheckIt?

As CheckIt is commercial software, and VOGONs does not allow links to pirate copies commercial software, I can't help you to obtain that software. It was very common in the late 80s and early 90s, and it is likely that many software archive sites that distribute such software as "abandonware" have a copy of it.

Ok I found it.
The tests for both COM ports were completed without issues.

Good. Maybe there is a wire broken in that short ribbon cable. What mouse driver are you using for your tests?

I have a Logitech and a Genius mouse. I've tried the Logitech and Genius drivers and CTMOUSE.

Use a pin and test the cables for connectivity.

Ribbon might be plugged backwards?
I would open serial terminal on com1 and start measuring pins while slamming keyboard, then try rerouting TX pin to leftover pins that didnt measure any output signal.
Sadly no um8667 documentation available 🙁 someone would have to provide pinout after tracing pins to rs232 sockets on another board/controller.

By any chance have you been playing with UM8672.SYS? See: Re: Ctmouse issue when loading drivers for UMC 8672 VLB I/O card