Troubleshooting a 5V Apple III

[Tony Duell]

> The PSU was borrowed from another, working 5V Apple III, so I'm
> confident it's good.

OK, so the replacement PSU was good when it was installed. However, this 
does not mean there's not a fault on the mainboard that's pulling one of 
the rails out of tolerance. Given that you have a voltmeter, I can't see 
any reason not to check those supply rails on the mainboard.

I find it curious... All the books I have on electrronic 
troubleshooting and repair emphasisis that the only wat to put something 
right is to make measurements and think about them before you change 
anything. And yet it appears that these days you replace parts in an 
attempt to fix the problem without knowing if said parts have anything to 
do with the fault. You knwo, if I ever meet the guy who decided that 
board-swappign was a good method of diagnosis and repair, along with the 
guy who decided that soldering (or even surface-mount soldering) was 
impossible in the field, I am... well lets just say it has something to 
do with an induction coil and his reproductive organs ;-)

> 
> Thanks for the suggestions.  I'll pick up a logic probe and report my findi=
> ngs.

Is the Apple III schematic on-line anyewhere? I might be tempted to take 
a look and suggest other thigns to measure/check.

-tony