First post, by Speedsalat
I recently aquired a nice little Commodore 286-16 and I'm very happy with it. However, I wanted to install a 287 coprocessor to make it really complete.
Unfortunately it doesn't like 287 coprocessors - and thats where I would need help. The coprocessor is always detected without any problems in the BIOS. However, as soon as it is utilized by software, the system hangs. It happens for example with Checkit 3.0, NSSI, ... It also happens with the Intel Coprocessor check tool "chkcop" (which delivers different errors depending on the utilized FPU).
I tried following coprocessors:
- An Intel D80287-10: chkcop hangs before identifying the coprocessor
- An Intel C80287XL: chkcop hangs after identifying the coprocessor but before any test can be performed
- An IIT 2C87-20: chkcop doesn't hang but produces an endless loop of "abnormal program termination" errors
It seems like a problem with the mainboard. However, I am not really experienced in this topic. The mainboard has some modifications done, which seems to be related to the floppy controller. I also reversed the changes temporarily - but this did not help. I also measured the traces and compared them to the datasheets - unfortunately I did not find any datasheet of the Headland HT12/A chip. The voltages seem to fit - CKM is high, VCC and VSS seem to be alright (the chip also gets warm) - the data pins are connected to the according pins at the CPU, Busy and Error are ~4.8V (strangely busy only dropped to 0.01V with the XL FPU - with the IIT I measured 4.8V all the time). I did also not notice any shorts or broken traces around the FPU.
Before I completely give up (which would be sad to give up on this really lovely PC), I wanted to ask whether you have any more suggestions what I could do in order to get the 287 working.
Thank you sooo much already