[Premium-Rx] Racal RA6790/GM Mystery Boards

[DAVEINBHAM at aol.com]

I just bought an A5 ISB board for my Racal RA6790/GM from someone on Ebay. 
The seller told me it was missing a few of the audio components. 
Sure enough, U12, T1 & T2 were at sometime removed from the board. Whomever 
removed them did a very good job of it, but I can still see the imprint of the 
starwashers that were originally under the screws holding the transformers to 
the board. All the components required to support U12 appear to be still on 
the board. Other modifications to the board are a coax cable soldered to the 
foil side of the board under J3. Hand lettering on the component side of the 
board just above this cable  says " rev. 5". Hand lettering between the original 
location for T1 and the edge of the board says " A5  615". Hand lettering next 
to J1 says " TO A4J3". 
There is also a ribbon cable connected to W1 that has 3 connectors daisy 
chained on it. The first two of these are connected to 2 other boards described 
below. Judging by the folds in the ribbon cable, it appears the A5 board lived 
above them in the radio this stuff came from.
Included with the A5 board were 2 other boards the same size as the A5 board 
bearing the numbers 23386  A09321. There are coax cables about a foot long 
from J2 & J4 on both these boards that are terminated in BNC jacks. 
Does anyone know what I have here ? 
Anyone have a schematic for the mystery boards? 

Kindest regards,
Dave
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