Hi all,
I've just opened up my Jupiter Ace and I think the problem I'm having
with it is far more severe than a blown CPU. It looks like while I was
testing it this morning the PSU was accidentally powered up, the +12(unreg)
connection made contact with the barrel of the power jack (-ve) and the
PSU's -ve line made contact with one of the first five expansion bus pins on
the topside of the board.
The CPU was getting very hot - I've since swapped the original NEC D780C
(1982 datecode) with a Sharp LH0080 Z80-A-CPU IC. The replacement is also
getting hot (takes about a minute for either of them to hit 50deg C). Output
from the 7805 is 5.04V steady according to my Fluke 25 DMM. Video is being
output and my TV can lock onto it, but the output is total garbage, no
difference if I remove the CPU and ROMs or have them installed. The garbage
is always the same, too, in case it matters. The replacement CPU is
known-good - it came out of a working Toshiba HX-10 MSX.
How should I proceed with this repair? I've got a Fluke 25 DMM and a Tek
466 storage scope at my disposal. Also, the schematics are almost
unreadable. I got them from home-micros.freeserve.co.uk. Anyone got a better
copy?
Thanks.
--
Phil.
philpem_at_dsl.pipex.com
http://www.philpem.dsl.pipex.com/
Received on Thu Dec 05 2002 - 12:05:01 GMT