NAD C542 continuous issues

Hi Guys,
My 2 NAD C542's are driving me nuts, they both have 'similar' problem but I've no clue how to tackle it...recapped, whole drive mechanisms replaced, voltages measured - nothing helps. I'm wondering if they're suffering from a known failure?

Unit 1:
- Complete laser assembly replaced
- Power supply fully recapped except for the 12V one as this one has decent (Fine Gold) caps, measured the voltages - good
- Voltages measured - all OK
- Relays bypassed (just for testing purposes)

Problem:
- Sometimes it doesn't fully turn on, the green LED turns on and that's it. The other time it turns on, reads the TOC, then the 1st track but it's skipping through tracks, trying to change track or go from the first to last track sometimes it goes nuts and eventually shows -- ---- on the display.
- If it reads the TOC and you let it play untouched from 1st to last track, it will play the whole CD with no issues



Unit 2:
- Complete laser assembly replaced, still the same issue
- Power supply fully recapped except for the 12V one as this one has decent (Fine Gold) caps, measured the voltages - good
- Voltages measured - all OK
- Relays bypassed (just for testing purposes)

Problem:
- Turns on fine, CD spins but no sound from the laser and no TOC readout
- Every few seconds there is a short click from the relay, the voltage drops and comes back again, this can also be seen looking at the CD speed, it goes up and down every few seconds
- Very rarely it reads the TOC after a minute and plays but touching any button makes it lose it's mind
 
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