In 1979 I built a Ferguson BigBoard, CPM machine with (gasp) 64K of memory. I also built a power supply protection circuit with solid state relays that would turn off the supply if it was missing a voltage -- board required +5, +-12 and +24 for the 8 inch floppy drives. BG Micro had such a supply, so that's what I used.
Not being the finest builder -- and all this system was bare board, no such thing as Antec at that time, finally found a case for the board and both drives, but the power supply was external -- I had a mess of wires so I decided to neaten things up. Disconnected the PS cabling, neatened, re-routed and reconnected. Boy, it looked nice. Turned it on and it immediately turned off. Hmmm. What could be wrong. Tried stuff, none of which involved verifying where the power leads were going. Finally decided that my protection circuit had gone bad, took it out of circuit, plugged the supply back in and watched smoke rise from the cabinet. When you reverse all the power leads on the output strip and apply plus 12 to the minus 12 bus, it does nasty things, especially to that expensive memory. I found a deal on a populated Xerox 820 with all important 4116's (memory) in sockets for only a bit more than the cost of the memory chips and ordered from BG Micro, but only after the new stuff was enroute did I discover that the smoke got let out of a couple of tantalum capacitors -- my original memory was fine after changing out the caps. But it was too late to send the parts back, so that was how I ended up with the second single board computer. Xerox bought the rights from Ferguson and marketed the 820 for a short period of time. A change in the ROMS on the board made it think it was the original BigBoard. Ah, the good old days… Geep WA4RTS On Nov 24, 2011, at 2:43 PM, Neal Campbell wrote: > I go there a lot and frequently! I end up with a large part inventory > because my usual assumption is that the most expensive part is dead and > immediately order a replacement to be overnighted in, only to discover my > stupidity the second its too late to cancel the order. > >> >> Why is it we always go for the worst outcome first? >> >> I have been building and testing a computer today and everything was going >> smoothly until it just turned off. Would not power up no matter what! >> _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
