The RA1792
Page 8
The Front Panel assembly

The front panel assembly encompasses the Switch & Display Board and the Front Panel Memory Board (FPM). Both come in at least two flavours. Oddly it would appear that Racal only fitted back-lit LCD displays to the Mark 6 receiver. This required fitting a network of 16 light-bulbs behind each display. This in turn requires two additional pcb tracks on the FPM board.

The photographs above show a basic non-back-lit display board. The displays and switches are mounted on the front with the ICs mounted on the rear. All push buttons (keys) are magnetic reed relay type

The photographs on the right show two clearly different types of FPM board … the (earlier) light green version is clearly not as wide. This is because this is a pre-BITE FPM board. U31 and U32 do not feature on pre-BITE FPMs.

The FPM board, as its name suggests, is in part a memory board. Two EAROM chips, U13 & U14 (ER3400) retain such information as mode settings as input via the front panel keys. Also included on this board is the circuitry associated with the optical shaft encoder and in the case of the board in the bottom photograph, the BITE monitoring multiplexor, U31 and U32.

Finally, the FPM board serves to distribute all non-RF pathways throughout the receiver