[midatlanticretro] WTD: Morrow Wunderbuss Thinker Toys Motherboard Schematic/docs

I almost posted a lengthly explanation on the march group list before I noticed you posted the pic on cctech. The power supply in that circuit is a -12V not +12V. The voltage regulator part # on there is a 7912 which outputs -12V. The part that is blown on there is an electrolytic cap, not a zener (note the + sign on each end of the cap). Both of those parts below the 7912 are the same type of part. Caps always dry up and blowout--they don't last forever. That's why it's good to have a Variac when powering equipment that hasn't been on for a long time--a homemade current limiter helps too if no variac is available. But I'm not sure of the value, it can't be very high in value, possibly only 3.3uf or 4.7uf considering the size, this isn't very critical , so long as you keep it in the ballpark. The caps for the 7805 regulator on there beside it are only 2.7uf. I would suggest changing both of them, for sanity's sake--they both might be damaged. The other important issue is to check the traces for damages when you remove the bad parts. They could have burned through creating an open circuit. So you'll have to splice the traces back together if this is the case. Some skinny telephone copper wire always does the trick. And last but not least, is the 7912 voltage regulator. You should check the -12V power before you plug in any cards. =Dan [ My Corner of Cyberspace http://ragooman.home.comcast.net/ ] B. Degnan wrote: