17 Feb
2014
17 Feb
'14
1:32 a.m.
In message <bsovf9l51pr6bp1098bii2o7nkgmkoiq94 at 4ax.com>
Charles <charlesmorris800 at centurytel.net> wrote:
My PDP-8/A with two 16K core boards has developed a
flaky bit on one
of the boards. The failure is always in the LSB (11), but there is no
pattern to the addresses that I can discern.
The +20 volt supply appears to be ok (as is +/- 15 and
+/- 5)... it
was 19.86v, but adjusting it to 20.00 didn't help.
DHKMAD.DG runs beautifully with only the lower 16k
installed. But
while testing the upper 16k, eventually (30 sec. to several minutes) a
random word will fail with its LSB (Bit 11) in the wrong state.
Usually 1 when it should be 0 but *not* always!
Often this bombs the diagnostic program itself (I
suppose if it's
self-relocated to the upper field). So far the failures have all been
in field 6 or 7.
Any tips for checking currents/timing? Or should I
just replace the
G650, the H219B core stack, or both as a pair? They aren't easy to
find these days and my small chassis only has room for two core boards
that occupy two hex slots each - so they both have to be 16K boards,
as ADVENT requires 32K even though OS/8 runs in 12K :(
-Charles
My first thought is -check the bus-driver-.
On my PDP-11/05 several boards had problems with warming up in both
ways, either operational till warming up or (most often) fail until
warmed up.
Rolf.