Hello,
I have just this evening acquired one of the same units with similar fault, - the tray comes (partly?) out but the arm 'stays put'.
I notice that the belt is loose fallen off the drive pulley I expect.
I'll take the case off tomorrow for a detailed inspection, and look for clues.
My expectation is that the arm will only move out when the tray is fully extended,- a switch operated by the tray supplying the power to the arm motor or maybe providing a 'go' signal for the arm motor controller circuit. I doubt the belt being off would affect any of this as you would need the tray out to fit a belt.
In answer to your specific question.
Some components (electrolytic capacitors) can deteriorate over time and will affect an electronic circuit, possibly generate some smoke and 'bangs' though the latter unlikely on transistorised electronics.
Drive belts can perish, switch contacts and plug/socket connections can corrode/tarnish with time often cured by operating the switch or unplugging/replugging plugs + using a little WD40 or specialised switch cleaning fluid on the suspect component. That's just about it, spills of sugary liquid onto the printed circuit board (PCB) call for carefull cleaning before power is applied!
Please post any usefull 'stuff' you have acquired, I'll re-post when I've more to report.
John Hazell., April 2008