[PeterRoberts]

Martin,

Having had a read of the manual as to what the thick film actually does, it does sound very much like the same as a Plessey SL620/SL621. Its unlikely that in those days in particular that Racal would have used a Plessey device, but they may have made something that did the same job and created it as a thick film circuit. Mind you, finding a SL620/621 is not going to be easy either.

If the old thick film is dead you could try to carefully scrape away the encapsulation and see what is inside. You may be able to reverse engineer it or even find a fault. Some of these thick films did include tantalum capacitors and they don't age well.

If you are a member of the RacalRadio group on groups.io it is well worth asking there to see if anyone has this thick film or a gash board.

73,

Peter
G4DJB