23 Jul
2007
23 Jul
'07
12:52 p.m.
Josh Dersch wrote:
Picked up an Apple III this weekend in non-working
condition, and I
suspect the power supply is at fault.
Symptoms are: On power up, a rapid clicking noise is emitted from the
power supply (maybe 4Hz or so), and the power LED on the system's
motherboard pulses at the same rate.
This is a classic symptom of a switch-mode power supply that's
failing to start up, possibly due to a short on its output.
Such a short could be caused by a tantalum capacitor that's
simply gone short-circuit with age. The trick will be to
find out which one of the (possibly several) tantalum decoupling
capacitors is the bad one. An ohm-meter (multimeter on Ohms
range) will read the duff capacitor as a short circuit.
--
John Honniball
coredump at gifford.co.uk