7603 RO mech flaky


Bonjour a tous, Voeux Nouvelle Année!

The 7603 is used with 7L5 or 7L12 SA plugins.
All OK except both SA have a flaky RO, with several areas showing scrambled alphanumerics.
If I push on the FP of the SA, the RO is fine. I cleaned the edge connectors of both, and put contact cleaner in the 7603 backplane sockets, No effect.
Has anyone else seen this symptom, perhaps on other 7000 MF?

Mille Mercis,


Roger Evans


You may also need to clean the switch segments in the plugins that are responsible for changing the readout characters - you will find some of the cam switch segments just switch different combinations of resistors into circuit to define the current into the digitisers on the readout board. If the scrambled readout is always in the same character position, eg the third character, then it is probably due to bad switch contacts, if it is the same font character eg if 15Mhz and 51MHz both scramble the '5' but not the '1' then it is likely to be a fault in the character generating ROMs. Somewhere in the manuals you will find a table showing which characters are generated by each of the several ROMs.

It does seem odd that both plugins have the same fault so maybe it is the second explanation that is more likely. Do you have any other plugins that are OK?




Rodger: Mille mercis:

1/ Swapping into another 7904 MF, the issues are in the 7603.

Opened up, Voila, dirty board edge connectors on the backplane, folded biz card soaked in contact renew, cleaned all 3 compartments.

2/ Found corroded axial tant on the backplane, wonder how many others lurk inside 7603?

Best Regards,