Re: Power supplies keep crapping out on me...solved!

[scott@alfter.DIESPAMMERSDIE.us (Scott Alfter)]

(Yes, this is a reply to my own post.  Yes, the post to which I'm replying
is about six months old.  It took me this long to get around to tracing down
the problem and fixing it.)

I had a problem with Apple II (IIe/II+) power supplies quitting on me.  The
computer would run just fine for months at a time, then after I turned it
off one day, it wouldn't switch back on.  Some possible solutions were
offered, but I didn't get around to trying them.

I wanted to get my beer fridge running again after my recent move.  After
cleaning up the little bit of dusty mold that had accumulated inside the
fridge, I plugged my IIe back into the fridge (a cable connects the computer
to a temperature sensor and a relay that controls the compressor).  Of
course, it didn't start up.

I looked up the previous messages on this topic and set about to take the
computer apart so I could get at the power supply.  While doing this, I
noticed that the computer would start if the floppy controller was removed. 
As soon as the floppy controller went back in, it wouldn['t start.  Removing
the 1-meg RamWorks II, the LocalTalk controller, and the Super Serial Card
didn't make any difference; the computer would start without the floppy
controller, but wouldn't start with it.

Someone else might've thought that the floppy controller was bad.  I figured
that maybe it was trying to pull more power than the power supply could
handle.  I could've tried hotplugging the floppy controller and seen what
happened, but I didn't want to screw things up more than they already were.

One suggestion I had been given was that maybe a small-value (1-4.7 uF)
electrolytic capacitor in the power supply's startup circuit had gone bad. 
I didn't see anything in that range on this particular supply.

After a bit of googling, I ended up at the page in the Apple II FAQ that
covers power supplies.  It described my problems exactly--works for a long
time, then has difficulty starting up again.  I tried the suggested fix, and
now my IIe is running again.

If your power supply was built by Astec, there's a 220-uF electrolytic
capacitor near the transformer in the middle of the board.  It's rated for
10 WVDC, which apparently may have been under-specced.  The recommended fix
is to replace it with a same-value capacitor rated for at least 25 WVDC.  My
parts bin had some suitable capacitors rated for 35 WVDC, so I desoldered
the old part and soldered in the new part...a ten-minute fix that cost me no
money.  Cool. :-)

(One bit of unrelated weirdness I noticed when testing the fixed power supply
(prior to fully reassembling the computer) was that if you fire up a IIe
motherboard without the keyboard plugged in, the red LED near the power
connector will light up, but the speaker won't beep.  Plugging in the
keyboard got it to start up.  Is this behavior normal?)

The computer is now up and running, and now I'm ops-checking the beer
fridge.  It's getting cold like it should.  It's still ramping down to the
setpoint I gave it, but if the computer starts cycling the compressor on and
off after that (and I'm 99.9% certain it will), then I'm good to go.

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