14 Apr
2013
14 Apr
'13
7:23 p.m.
On Apr 14, 2013, at 7:53 PM, Jules Richardson <jules.richardson99 at gmail.com>
wrote:
On 04/12/2013 02:24 PM, David Riley wrote:
A simple open-collector inverter made from a general-purpose NPN
transistor should do fine. If you Google hard enough for it, you
can find examples; you'll probably at least need to put a resistor
on the base so you don't blow it up, but you might not need one on
the collector. If you can't find anything, let me know, I probably
have an example stored somewhere. Of course, if you're just going
to make a wiring harness for the ATX supply and wire the thing on all
the time, that solves your problem too. But the switch on the Mac
itself is only going to switch that power-on line; if you have an ATX
supply with a switch on it (which seem to be rarer these days), that
would do the trick.
If it turns out your logic board is OK, do consider trying to repair
your power supply; the 6400/6500 ones seem hard to find on eBay. Be
sane about it, though; my Quadra 700's PSU had a bad connection in
the transformer which supplied the +5v standby, which is basically
unfixable (there's absolutely NO WAY I'd be able to find a
replacement for that part; I probably could have reverse-engineered
the schematic and figured out how to MAKE one, but it wasn't that
precious to me since Q700/IIci/IIcx power supplies are pretty
reasonable on eBay).
- Dave
The PSU is probably pretty similar to an ATX
supply in that the
motherboard pulls a pin high or low to soft-switch the supply on and
off. I'm having trouble finding a pinout for the 6400's PSU
Just an update on this - with the 5x00 bus pinouts that you gave me, I was able to
confirm that the 6400 is the same (at least as far as the PSU signals) - so thanks for the
link.
Unfortunately, it's also confirmed that I've got a dead PSU; I've got no +5V
on the standby/TRKL line at all. I've done a few basic checks for open diodes,
transistors etc. on the AC input side, and things seem OK there.
I think I have a spare ATX PSU from a PC somewhere, so I may try that if I can contrive
something to marry up the different power-on signal (or I suppose I could just hit the
power switch on the back of the Apple and then turn the PSU on manually, just for testing
purposes) - there's probably no point my spending time fixing the Apple's PSU if
the system board is toast anyway...