Is my ECU cactus? error code 53

Hey fella's
Driving my car today (1990 turbo) and she decided to throw the check engine light,did the check and it threw 2 codes,53 and 42
The 42 is something to do with the vss so shouldnt be much of an issue but 53 is meant to be in internal ecu error for the knock sensor circuit.
It already threw code 52 (knock sensor) i replaced that with the ATS racing one and all has been good.
Question is,is the ECU gone or is there a way to sort it out (already tried a reset)
If its had it does anyone have one for sale?wouldnt mind picking up a good AFM at the same time to see if it improves my fuel economy.
cheers guys