On Tue, Jan 13, 2009 at 6:31 PM, HavNet <jason at havnet.net> wrote: I'll give it a shot. Nice. I wanted a Computhink back in the day - I already had a bare 8" drive and couldn't afford a 2040 when they were new. Eventually, used 5.25" drives came down in price (some time after the 1541 and 2031 came out), so after a time, I went with genuine CBM disks. OK. Given the scenarios I can imagine for your setup, it's an unfortunately easy explanation that satisfies your symptoms. Interesting clue. Not me personally, but I've seen all sorts of strange behavior from bad ROMs (it doesn't happen often, but it does happen). Well... do you have any other utility ROMs? BASIC 2.0 and BASIC 4.0 PETs have a simplistic "TIM" machine language monitor built-in. You can invoke it by SYS 1024 (or any other location with a zero byte), or there is an official entry point that I'm forgetting off the top of my head. Whether you have an add-on monitor program or use the built-in TIM, the syntax for a memory dump is the same. At the "." prompt, type "M B000 B020". Since you say your DISKMON program is at "11*4096", that's the entry point. I'm guessing things will look OK since you invoke it and you get a prompt back. What's probably happening is that the initialization code is patching "CHRGET" in zero page, which is normally used to fetch BASIC keywords for tokenization, but is often patched to extend the interactive command set. In your case, I'm guessing there'll be a pretty simple patch to check for an initial "$" and either jump off to DISKMON commands or back into BASIC for regular commands. Speaking of that, after you invoke DISKMON, do _all_ commands give you the checkerboard or just DISKMON commands? That can help distinguish where things are going wrong. I'm guessing that your interface board has an EPROM - one possibility is that your EPROM is undergoing bitrot from age. I do not have any technical info on your interface (I wish I did), but if you have schematics or a ROM dump, that could be very helpful. Reverse-engineering the interface would probably not be _too_ difficult, but reconstructing the firmware from scratch is rather unlikely to be feasible. So does anyone on the list have a ROM image for a Computhink interface? Schematics? One other resource to invoke is to suggest you join the CBM Hackers mailing list and ask questions there - there are many people on it that know deep and intimate details about PETs, but to be honest, there's more known about C= machines and peripherals than 3rd party devices, so the better the docs you have with your interface, the better off you might be. -ethan