When checking for continuity of questionable traces, IMO it's best
to
figure out which pins of which IC's are being connected by the suspect
trace.
Then use the DMM to measure directly between the involved pins.
Connecting
the pins of the IC's together is the ultimate goal, so it's best
to confirm
that it's being achieved. In other words, you want to check from one
end to
another end, since that's what really matters. Also, trying to get a
good
connection from your probe to a corroded trace is not easy.
Really, on something like the PolySix, what I would suggest is to print
out the
schematic of just that one board, and "buzz out" with a meter the
connections in
the area that is corroded. Highlight the traces that have
been tested as you go.
If you just try to test the traces that you notice
that look bad, it's easy to miss
something.
My
$0.02
Bob
Message
Re: [PolySix] checking connections
2018-07-16 by <backshall1@bellsouth.net>
I absolutely agree with this. A lot of the bad traces on the board just
look like they go to a “via” that goes through the board to the other side.
Unless you test all the way from chip to chip, you haven’t really proven
anything. Since most of the damage is on the D00-D07 data lines and there are
eight of these, and each one goes to multiple chips around the board as well as
a couple of connectors to other boards, there is a whole lot of testing to do. I
think it was Andy Jury who first mentioned to me that he tests everything from
connector CN10 back to all of the other chips. That means that in order to prove
D00 is working, the following continuity checks must be done:
CN10-4 to IC31-6
CN10-4 to IC26-13
CN10-4 to IC28-4
CN10-4 to IC33-12
CN10-4 to IC34-4
CN10-4 to CN06-3
And that’s just for the first data line out of eight. I have been using
this method ever since and it’s really the only way to make sure you don’t miss
anything. Oh, and since the two 74LS08 chips look like they are in bad shape,
there is likely damage on the DB0-DB7 lines as well, between the 8048
microcontroller and IC30/31
Don B.
Sent: Monday, July 16, 2018 11:34 AM
Subject: [PolySix] checking connections