E1 Error code on Fujitsu AOT45LJBYL ? Everything tests perfect...what am I missing?

[Wisha]

Hi all,

Have Fujitsu ducted unit. It was producing an error flash, but simply turned it off / on and it went away.

A couple of months later, the flash is back (reads as an E01 error - coms), and the reset doesn't help.

Symptoms are fan mode works, cooling mode (fan runs, but no compressor - but its winter here now, so the compressor wouldn't be required anyway), heating mode, nothing runs.

I contacted Fujitsu and they sent me the technical docs to test:

Only 20odd V on the outdoor signal wire (so outdoor unit com issue).
The Diode Bridge (all good at spec).
ACTPM (all good, except P/N connectors read as 710K- Should be 720 - 900, but surely 710K would be close enough)?
EEV (all good)
Fan motors (all good)
Compressor ( all good)

Pulled both boards out. The power board looks perfect. Is it worth moving the varistor, and then putting back to the original position? Looks all good though.
The control board has all fuses ok. Did notice some very mild 'off colour' on the board around the JPZ transformer/ Q1 transistor/ zener diode/ R2/ R6 resistor, C1 cap area. The resistors look fine and measure to spec, the cap measured to spec, I pulled the transitor (Q1) and that was fine as well.

So this thing has me stumped?? All the Fujitsu tests seem good, no fuses blown, and it was once fixed by simply reseting??

Any hints and tips would be greatly appreciated

Cheers