User`s guide

If you open the power supply up (WITH THE MAINS PLUG OUT!) you will find a
capacitor C7 near the transformer in the middle of the printed circuit board (a
220 uF 16V capacitor if I remember correctly) change it for a 220uF 25V 85
degree Centigrade rated capacitor and it should clear the problem up.
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From: Jeff Allen
I've been trying to fix several dead Apple II power supplies from a local
school and have managed to bring back one from the dead now. The fix was to
replace the 10V, 220uF electrolytic cap with a new one. (I used a 35V piece).
Assuming that the board markings are useful, this was C7, on an Astec board with
the datecode "T8312" on it. I'm curious if anyone else that has replaced that
cap has noticed any browning of the pc board where the leads enter from that
27ohm 2W 'R4' beast. ....
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From: Rubywand
Very interesting! A bad C7 would screw up the regulator's feedback voltage.
Even better, Jeff Allen's observation of the heat spot on the PCB seems to
indicate that heat from the nearby 27 Ohm power resistor is responsible for
shortening C7's life. If there is some way to eliminate this hot spot-- e.g.
using a 10W resistor, perhaps with a heatsink attached, or mounting the resistor
on the power supply's metal case-- many II+ and IIe power supply crashes might
be prevented.
______________________________
From: Rubywand
013- To my horror, this morning when I flipped my GS ON
it emitted a rapid chirping noise (maybe 8-10 times a
second) and refused to start!?
The chirping usually means that the PS load-detect circuit thinks that the
load is too great (i.e. that it draws too much current) or that there is an
'open' in a major output line (i.e. that there is, practically, no load at all).
This can mean that the power supply is bombing and, so, almost any load is
too great. It may, however, mean that a short has developed on the motherboard
or on a Slot. It can, also, mean that a break has developed somewhere in the +5V
line or at the connection of the connector to the motherboard.
One test is to unplug the power supply, remove it, and do some load tests.
(Note: If the PS has a slotted adjustment pot, mark its position and, then, turn
it back and forth in case it has become stuck at a dead spot on the control.)
If the PS can deliver +5V with a 3 Ohm power resistor connected across the
+5V and Ground lines, +12V with a 15 Ohm power resistor connected across the
+12V and Ground lines, and correct Voltage for -12V and -5V lines into, say, 100
Ohm resistors, then the PS is likely to be okay.