9 May
1999
9 May
'99
11:50 a.m.
Tony replied to my IMSAI power supply woes:
Pull out all the boards and disconnect the rectifiers
from the
secondaries. Does the transformer still get hot? A shorted diode or
smoothing capacitor will make the transformer overheat...
The DC voltages were OK, which I assume means that the diodes, caps, and
regulators are OK. But next time I have the thing on my workbench I'll
check it.
What are the ratings? Could you replace it with 2
transformers (one for
the 16V rails, one for the 8V)? Can you rewind the old one (it's not that
hard to do)?
I don't know about the transformer's ratings, as they aren't printed on
it or in the docs. The primary has taps for 10% overvoltage and undervoltage.
The supply outputs are rated for +8V at 28A (ripple valley to 7.5V) and +/-18V
at 4.5A each (ripple valley to 13.5V).
It's probably easier to rewind the transformer
than replace it with
SMPSUs.
I've never rewound a transfomer, but SMPSUs are pretty easy. If I have
to replace the transformer with two or three new ones, the historical
authenticity of the power supply is already shot, so I might as well replace
the whole thing.