Alpine CDA-7878 laser fix help

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I bought some neutral-cure silicone, glued the heat shield in and reassembled the unit. I pressed the reset button and fed a CD in only to find the error message had changed to "no disc". I tried to eject the disc and there was no reaction so I took the lid off again and moved the CD load/eject gears manually to eject the CD. Now it won't even pull a CD in when I offer it.

When I pushed the source button (when the CD was in) from tuner to CD, the CD rom made a short mechanical noise then a second later made another short mechanical noise but nothing else happened. Could the laser need alignment since I have removed and replaced it? Should I try turning the laser power pot 1/8 turn (after marking the original position of course)? I have no access to a scope.

Or could it be the small 4mm OD spring that popped out from I don't know where when I disassembled the laser assembly? I left it out when I reassembled it. What tells the unit that there's a CD to pull in - is it the 2 LEDs as shown in the pic below or something else?
 

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I'm not sure how it knows a disc is inserted tbh, it could be mechanical (microswitches) or optical. That spring looks typical of the kind that often support the laser pickup chassis, usually four, on in each corner. Leaving it out (whatever it does) could mean something isn't supported and is jamming.

Laser pot would make no difference for what is happening now as it appears something has gone awry with the disassembly and assembly :(
 
Yes I'll have to disassemble again and try to find out where that spring came from. There is definitely only one spring though and I suspect it is Nr 71 in the pic below, which is from the service manual of the Alpine F1 CDA-7990R which uses the same CD rom. Thanks again.
 

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