8 Sep
2019
8 Sep
'19
2:21 p.m.
I guess I should have been a little more specific about the memory issues I
was having when I made this post. For the most part these issues seem to be
scattered all about memory. Also, while the XXDP I have been running has
been catching more or less the same addresses every time I run it, someones
it misses a few or adds a few new ones. Moreover when the tests are done, I
can read and write to the addresses using OTD just fine, which makes me
think the chips that are bad (if they are bad, and it isn't some power
related issue) are more flaky than dead.
I put one of the outputs from a run of the XXDP test on a pastebin below.
https://pastebin.com/mF6qWs0U
On Sun, Sep 8, 2019 at 4:01 PM Jerry Weiss via cctalk <cctalk at classiccmp.org>
wrote:
On 9/8/19 3:20 PM, Noel Chiappa via cctalk wrote:
Noel's approach is valid and I have done the same on several boards.
Sorry I don't recognize the vendor of your board.
I would also suggest checking the voltages on the board, especially the
-5V for the memory chip if the memory faults are scattered across the
memory space. The circuitry on the upper left of your picture is
probably a NE555 that is used as a charge pump to generate Vbb from the
LSI power supplies.
The larger capacitors are probably tantalum (Kemet?) and should have
aged better than electrolytics of the period.
Jerry
From:
Mister PDP
listed back there were numerous bad addresses all
over memory.
...
I cannot find schematics for any of the boards
.....
With the completed chart in hand, given a failing word (address and bad
data), you can work out which chip is at fault, and replace it. Repeat
for all memory errors.