Compupro 8085/8088 switchover problem.

Hi Guys, Been working on my Compupro system over the holidays - got the 8086/8087 system booting CP/M-86 reliably finally (yeah!). Also have an 8085/8088 CPU that I am trying to get running. All other parts of the system are exactly the same config except that the boot ROM selection is (0) 8080 standard boot instead of (4) 8086 standard boot. The system starts in 8085 mode, and always boots CP/M 2.2 (8080) reliably. I have a couple of different 8/16 boot disks which have an 8085 first stage boot, which then switches to the 8088 and loads CP/M-86. So far I have managed to make the system boot CP/M-86 three times (and only three times) from two different disks in this configuration. In all three cases, once it booted, CP/M-86 ran reliably as well (I even tried tapping on the cards to detect physical problems, and it runs perfectly). On every other boot attempt (and there have been quite a few), I can observe the system load the first block (head load/unload), and then load another block (head load/unload) after which it goes silent. If I put in an 8086 boot disk (which would be "invalid boot code" to the 8085, the system dies after reading the first block - which suggests that it always gets at least part way into the boot cycle. My guess is that it is not transitioning into 8088 mode correctly. I've double checked the switch settings, and all matches the Compupro suggested configuration. Looking at the schematic, there is not a whole lot of circitry involved in switching from one to the other - I have removed, cleaned (chip and socket) everything even remotely related to switching the CPU to no effect. Next step is to begin tracing it with the scope, and trying to figure out exactly how far it is getting - I'm guessing it won't be an obvious "it stopped here"... This could be a little tricky to figure out. Just thought I would check here and see if anyone has experience with this system and can offer any ideas of likely things to check. 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