OCEANRADIO wrote:
snip
Luckily, I found two burned up resistors in the power supply. I
substituted a spare power supply and the computer works fine, but the power
supply is outboard so I need to fix the original. So here's the problem: the
two little resistors R4 and R5 (1/2W) are marked brown, black, silver, gold.
The translates to me as .1 ohm. Is that possible?
The two were in parallel (electrically and physically) and it looked as if
there was an arc between them that burned them both up. There shouldn't have
been any voltage between them, given that they were in electrical parallel, and
they shouldn't have overheated, I wouldn't think, with such low resistance.
snip

The arc path across two parallel resistors sounds like the result of a
lightning strike.

"The Art of Electronics" by Horowitz and Hill (2nd edn. 1989, Cambridge
Univ. Press) has a good write-up on computer power supplies, and has the
complete schematic for typical one (an old Tandy design).

73,
Ed Knobloch