9 Apr
2004
9 Apr
'04
8:42 a.m.
Have yuou
checked _all_ the electrolytics, even the low-value ones? On=20
both sides of the isolation barrier.
I've replaced all the electrolytics on
the LV side that I could see. I've
just noticed a 1uF 50V that I missed - I don't think I've got a 1uF 50V 1=
05
deg C in stock though. Have you looked for a current sense=20
resistor that's gone high?
There is some visible heat damage around some
fusible resistors, but they checked out fine. There are two diodes in the vicinity
of the FRs that I
haven't checked yet. I really need to get this thing back on the bench fo=
r
testing.
Right. Never heard of them... Of course some companies then went and
reverse-engineereed the unit to put the info in their service manuals.
The Tandy M3 and M4 technical manuals contain what appear to be
reverse-engineered schematics of the Astec PSU boards. Well, they claim
to be PSU schematics, but actually could never have worked as drawn. I
speak from experience, having produced a more accurate (I hope)
reverse-engineered schematic.
This may mean they didn't actually design it,
but bought it in from=20
somebody like Astec who didn't supply schematics.
Looks like that's what
happened - the PSU bears the logo of a company cal=
led
Phihong. What really annoys me is that they went to the trouble
of picking a plast=
ic
that would shatter when you removed the case screws. Needless to say, the
Actually, I object to self-stripping [1] screws going into plastic anyway.
[1] A much more accurate description than self-tapping :-)
-tony