[Amps] Alpha 87A fault 33 when pressing TUNE DOWN

[Dave]

Hi all

Looking at an old 87A for a friend. 
This is a 91xxx s/n without AlphaMax and NO updates done to amp. 

Originally faulting with fault 8. Replaced bad RX PIN diodes with 1N4007 diodes and TX PIN with pair of UM4006D. No more fault 8. 

Now whenever you press TUNE DOWN it immediately faults with fault 33. (Tune motor failed to initialize).

Another clue is on power up both Load 
LEDs flash but only the TINE UP LED flashes twice. (Tune down does not flash). But Tune Down LED does light when pressing Tune Down. 

Any ideas appreciated   

Dave wo2x

Sent from my waxed string and tin cans.