My experience in owning a Regina 940 for 19 or so years is that the CPS will rarely if ever throw a code. Replacing it when suspect is good practice as it can shut you down. The radio relay can be a problem, though I've never had it, replaced it a couple of years back as a precaution when I had the exact symptoms you have.

You need to check/replace the main fuel pump relay, that is usually the culprit. It gets hot and the solder joints crack. Pull the relay, pop the cover off and check the solder joints with some magnification. The 3 big ones usually crack. I had 2 relays and both had cracks in the same locations. Re-solder them and you will be back in business.

I have found the coil amplifier to be dead nuts reliable. I have 2 of them also, bought 2nd one when I was chasing the same problem. I have cleaned the connection of the coil to amplifier like once and put a small amount of conductive grease on it. Currently running the 1993 one.

Of course, your mileage may vary, but I'd check the relay behind the ashtray first.

Mike