[Collins] Help: Collins 75A1 Wiring don't Match Schematic

[forum4ll at verizon.net]

I examined this Collins 75A1 SN#486 further. The major difference between this and one that conforms with the 3rd edition, SN#1417 is the use of B+ (hot) switching in the earlier versus ground switching in latter version. I may suggest to my boss to put this one away until we find a schematic.

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On Thursday, July 19, 2018 forum4ll <forum4ll at verizon.net> wrote:

I've been repairing a Collins 75A1 for my boss this past month. It has a low serial number in the 400s. There are some serious discrepancies in the wiring when compared to the schematic (3rd edition Collins Instruction Book) and another 75A1 with a higher serial number. Here's a list so far:C87 minus side wiring is not attached to center wiper on MAN/AVC/CW switchMAN/AVC/CW switch has a wiper to wiper instead of a MAN to AVC jumperExtra wire coming from the wiper on Rf Gain pot. Has three instead of two wire connectionsOuch, standby relay terminal has B+ connected from R43/R49 node instead of being grounded. Shocking!
Missing B+ wire from R43/R49 to R48/C81CR51 is connected to #8 pin and ground instead of pins #8 and #6 where the latter is terminated at standby relayThe Off/Fil. On/B+ On does not have one of its center wiper connected to ground. Have not finished its trace but there is impedance. 

Was there a revision to the wiring on the 75A1? Is it reflected in the 1st and 2nd edition of the Instruction Book? Some of the soldering looks fairly original like the wiring of the Off/Fil. On/B+ On and MAN/AVC/CW switches. Then others were definitely done by a hobbyist. Any suggestions are appreciated.


Thanks,


Lyman