HAAR@gmr.COM (RLH) (11/15/88)
In INFO-CPM 88-248, Mike Norris asks about a problem in which
his S-100 system fails to boot, but when he removes some "other
boards" it boots and then boots successfully after insert the
removed boards. This kind of behavior is symptomatic of bad
connections between one of the boards and the S-100 socket.
Try pulling all your boards, cleaning the sockets with spray
contact cleaner (use a good quality product designed for
electronic equipment), and claen the boards' edge connector
fingers by rubbing with a soft pencil eraser and then spray
them with the contact cleaner.
I have the same problem with my S-100 system but infrequently -
once every year or two. When this has happened, it has usually
been sufficient to pop the boards lose and re-seat them in the
connectors. I have gone to performing the cleaning process
as part of the annual preventive maintainance and haven't had
the problem for several years.
I have talked to a number on DEC service technicians who say
the second thing they do on service calls (after check the power
switch) is to reseat all the boards.
As I understand it, what happens is that there is some oxidation
off the metal surfaces of the contacts that builds up and acts
as an insulator. This happens even on the two surfaces of an
edge connector where they are in contact. Better immunity to
this kind of problem is one of the reasons that pin-in-socket
connectors like those used in the VME bus are popular in
industrial systems.
Bob Haar
GM Research Labs