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Lester
The RA drive is not working it should have resistance with power on and indeed should rotate at sidereal rate, the DEC pinion with power on should be nice and hard almost impossible to move. So, you definitely have an RA PCB issue.
Just check the controller is in sidereal mode and terrestrial mode? Have you also tried a cold boot?
The motor encoders outputs for RA/DEC (and motors) are controlled by U11/12 PIC micro-controllers & CPU. These are interchangeable. My best bet is that you have a bad RA motor encoder IC or maybe one of the PIC micros, not so sure about DEC might be ok.
I have seen funny movements from DEC & RA motors before and this was the PIC micros U11/12...amongst other ICs that were damaged. These IC's rarely go bad but I have replaced qty 2on same board.
Rene said he has never seen a "H" bridge (LMD18210T) fail so I'd discount this for a start though you never know.
The only other possibility is a bad EPROM (U7) or CPU. Of course you need a suite of IC's on hand to check all this.
I'm doing 2 Gemini's ATM.....one is ok just about to send off, the other had a few faults, nearly all fixed now, just waiting for U16 motor encoder IC from Losmandy.
Oh the sticker on the motor encoder IC is just a firmware revision tag and so far as I know these are interchangeable from one PCB revision to another...but that said you would never remove them and replace them as they would be damaged on removal de-soldering. You replace them on spec...that is if replacing CPU EPROM and PIC micros didn't fix issue and voltages measure ok.
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