Alrighty then, ........With a known-good Ext.Supply attached, then I would begin
by measure'ng the Main Printed Circuit Board's 5 volt distribution....see if its really
there and would amount....check across any 74xxxxx series TTL chips you find
there, caty-corner.... try the smaller scale integration type with a total of 14 or 16 pins..
Common return is usaully pin 7 (8) and +5 is 14(16)....known as VCC
... a lot of those style chips, however are analog op amps , in the same kind of package....there you will find they use --(neg)5 volts as well known as VEE....lets see......
IC1 has both, the NJM2069 VCF chip.......pin 1 is return, pin 22 is +5v, pin 12 is --5v...]
is one example.....If those voltages are there, then the problem is more sinister, and
now you get to become a computer techie to isolate the real prob.....usually this means
repair-by-substitution......obviously, only the socketed chips lend themselves to this....
I've tried myself to obtain the larger chips......some are common, the one mentioned
above is extreamely rare......Ok, so let me know if the V's measure ok
Dan