Tom, On Wed, Aug 11, 2021 at 11:05:59AM -0500, Tom Uban wrote: > Ok, I was going by the appearance of my case being the older style. I had not > considered the number > of PROMs, but now that you mention it, my old Ferguson Big Board (which was > an 820 clone) only had > two PROMs.
If you still have any 8" floppies from your Big Board, these will probably boot and work in the 820 as well as 820-II. ... > >> At some point, I need to ask someone to make me bootable 8" floppies, but > >> I suppose I need to > >> determine if it is 820 or 820-II first... > > I can able to help you with floppies. The floppies are standard > > IBM 3740 Single Density and easy to write with Imagedisk software > > and a PC-connected 8" drive. > What do you use to connect an 8" drive to a PC? This adapter is useful: http://www.dbit.com/fdadap.html But, if your floppy doesn't require a TG43 signal, you could just wire a custom cable with no logic needed, or get something like this on e-bay: https://www.ebay.com/itm/114924378003 Additionally, some PC floppy controllers do not work for some kinds of floppy encodings. Here is the article I used as a guide. I've been using an Adaptec AHA-1522A SCSI+Floppy interace, which has a good FDC chip for optimum floppy format support. https://retrocmp.de/fdd/general/disk-imaging.pdf > > Both the swithing supply in my 820-II and it's external 8" drive box > > had failed. I replaced the supply in the 820-II case with a modern > > switching supply that easily fit. The HV bleeder resister for my CRT > > was arcing, so I replaced that. I replaced all the electrolytics on > > the monitor board. I also replaced the sockets for my ROMs, as some > > of their contacts "sprung" when I replaced the chips, but I do not > > recommend doing this unless it is absolutely necessary and you have > > good tools and practice. > I had not turned on my box for a number of years, but when you posted, I > decided to try it and it > worked perfectly, which I suppose is just lucky. I do have the tools and > skills to work on it if it > were to fail, but won't likely make changes unless it does. I'm all for not fixing it if it's not broken. But, I do suggest careful inspection of the electrolytics on the motherboard and monitor, especially since the monitor board is right above the logic board, so if a cap phsically leaked, the corrosive stuff that comes out could drip onto the logic board. I see this mostly in SMD style electrolytics, but have seen those like the ones in my 820-II physically leak, and the damage can be serious. > > The 820-II restoration was a fun and rewarding project. It is well > > documented, easy to work on. It was also my first ever CP/M computer. > > When I was in high school, the 820 motherboards were readily available > > for $75. > > > > Mark > It sounds like you had a good time, which in my opinion is the main goal! > > --tom -- Mark G. Thomas <m...@misty.com>, KC3DRE
