1 Sep
2011
1 Sep
'11
11:23 a.m.
On 01/09/2011 13:30, Mike van Bokhoven wrote:
Well, another step forward. Thanks to Tony's
advice, I continued
investigating the video output, and found another dead IC (74LS51 this
time). I'm beginning to wonder how a machine could end up with so many
faulty ICs; that's two in just the video circuitry. Maybe the original
PSU short to ground did something horrible.
I doubt this is the cause, but I once had a similar effect with a BBC
Micro and a Torch disk pack PSU. The Torch processor, mounted upside
down inside the lid of the BBC Micro, fell off and shorted something on
the main PCB below. The PSU apparently shut down, but had a serious
voltage overshoot when it started up again, and put about 8V or more
onto the 5V rail. That took out quite a few LSTTL chips. Oh, and the
way we found out which ones was to put a big bench 5V PSU on the machine
and see what got hot because it was drawing too much current...
Silly question of the day: I'm guessing no-one
would have any idea where
I'd find a 14.25045MHz crystal in New Zealand...
No, but the standard crystal in an Apple ][ is a 14.318MHz crystal, and
that's a standard so should be very easy to find. I wonder if yours is
a special value for a non-US market? But AFAIR even the Apple Europlus
used 14.318MHz.
--
Pete Peter Turnbull
Network Manager
University of York