24 Apr
2016
24 Apr
'16
10:18 p.m.
On Sun, Apr 24, 2016 at 1:06 PM, Mark G Thomas <Mark at misty.com> wrote:
Hi,
So far, the only M8330 prints I have found are extremely fuzzy, so I cannot
make out the IC identifiers or match them up to the equally fuzzy
schematic.
You do know about bitsavers.org, yes? Al has lots of very clear scans of
DEC prints. Keep in mind, though, that these are hand drawn prints -
sometimes you have to zoom to 150% or 200% to make out particular
letters/digits.
By board-inspection I identified the 74S74
"run" flip-flop, and in fact I
can un-stick the RUN state by briefly grounding CLR, but still cannot
DEP or EXAM from the front panel -- it gets stuck back with RUN on if I
hit either DEP or EXAM again.
The power supply voltages are right-on. I've reseated and repositioned
the boards. The connectors are very clean. Wiggling boards doesn't change
any of the symptoms. Wiggling switches doesn't affect anything. This is
a very clean 8/e.
Check not only your voltages, but your power waveforms. Also, I remember
having an issue involving a race condition with the DC OK line, which is
not often considered when one is checking power supply voltages. If the +5
rail isn't solid *before* DC OK comes up, this will lock up things. Have
fun -- Ian K7PDP
--
Ian S. King, MSIS, MSCS, Ph.D. Candidate
The Information School <http://ischool.uw.edu>
Dissertation: "Why the Conversation Mattered: Constructing a Sociotechnical
Narrative Through a Design Lens
Archivist, Voices From the Rwanda Tribunal <http://tribunalvoices.org>
Value Sensitive Design Research Lab <http://vsdesign.org>
University of Washington
There is an old Vulcan saying: "Only Nixon could go to China."