Odd FDC problem (Compupro)

Hi Guys, I've got a Compupro 8086 based S-100 system which has been on the "to do list" for a while, and yesterday I finally got the CPU reference manual which was the missing piece ... I've "almost" got it working, according to the docs, it should flash the drive select light about once/second with no disk in the drive, as it tries to read --- this it does. The odd thing is that if you put a disk (any disk) in the drive, it immediately stops selecting it - it's as if getting the index pulses from the disk prevents the FDC from proceeding ... Sometimes, usually after taking a board out to check something, it will actually try and boot from the disk - If you put Disk-2 of the Compupro CP/M 86 distribution in the drive, you can hear it boot, it seeks a bit and obviously reads a track or two - after the first seek, you can see the RTS+DTR lights come on on all three serial ports, which suggests that it has come up enough to init the serial ports ... but I do not get any output on any of the three ports. I have the FDC configured to use User port 7 of the Interfacer-4 which is how it is configured (standard Compupro setup). (anyone familier with Compupro have any experience with this?) But my main problem, is that most of the time, putting a disk in causes the FDC to stop selecting the drive - it resumes selecting once the disk is removed, however it does not access the drive while the disk is in - since this is a 765 based controller, you can see the background polling as a dim glow of the select led. Anyone have any ideas what would make an FDC behave like this? Since it does get further infrequently, I believe it is not a component failure ... most likely a dirty socket or connection - but for the life of me I cannot figure out what would make an FDC stop trying to access a disk only when it is getting index pulses. Btw, I have checked the drives on another machine and they appear to work fine. Regards, Dave -- dave04a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.parse.com/~ddunfield/museum/index.html