20 Oct
2011
20 Oct
'11
12:58 p.m.
Yeah, it's been awhile since I went over it (using
the unofficial
schematic on HPCC) but I recall that the power looked fine but I was
THere are of course several power lines, I assume you checked the lot.
getting no clock signal at all. The 65 powers up and
a few segments on
the right hand side light up, but that's it. I seem to recall that the
custom chips on the display PCB generate the clock signals, but I don't
have any spares so I have no idea if replacing them would fix the problem...
The master clock oscilaltor is part of the anode driver IC on the
keyboard/display PCB. The 2-pahse clock signals from that are sent to the
CPU hybrid circuit whey're the're converted to different votlage levels
and then sent out to the other chips i nthe hybrid and the ROMs.
If you're gettign nothing out of the anode driver chip clock pins, it's
most likely this chip has failed. But do checl the LC 'tank' circuit
connected to this chip. That's for the clock oscilator, of course.
AFAIK you cna use an anode driver IC from any of the classic-series HPs
(35,45,55,65,70,80 -- note that the HP67 is not really a classic series).
Not that htat helps much.
-tony