when connected, the disc rotates for a few seconds then stops, then rotates again and so on.

I have had similar cases before that were solved with a change of pcb, but this particular case leaves me with no options.......

patient disc + pcb donor + patient rom ----> same result (spin up/down constantly) ------> discard pcb problems

patient disc +pcb donor + rom donor ---> same result ----> discard corrupt rom problems

Isolated head contacts ---> same result ---> would rule out preamplifier or head problems

Am I missing something??

motor damage???.... but it would be the first case I see in this series and even less when it turns (not blocked).

Has anyone ever had this happen to you? And most importantly, what was the solution??

How does a working drive behave when you isolate its HDA?

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A backup a day keeps DR away.

hello fzabkar, your opinions are always welcome, thank you

I know, it doesn't make sense, but it does exactly the same thing, it turns and stops turning after a few seconds, turns again, stops again........

It's haunted!!!!!!!

It appears that the firmware is designed to spin up the drive and then check the preamp, in which case ISTM that the preamp/headstack must be faulty.

You might like to compare the resistances between ground and each of the preamp supply test points (+5V & -5V). You could also measure the voltages at the HDA contacts, eg the read channel test points (TV9 & TV10).

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A backup a day keeps DR away.

In WD the usual is the opposite, first check the preamp and then spin up, that's why I discarded preamp or head problems, but as I don't believe in witches, I'll do the checks.

Thank you fzabkar

Yes, it is most reasonable, PCB and Rom are discarded and the motor is very unlikely, there are few options,

What I don't understand is the reason for the continuous spin attempts,

That’s what it is.

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