CD Player malfunction when first turned on
I have disassembled the unit so that I can observe the CD player in action. There were sounds prier to disassembly that were unexplained. In operation, with observation, the carriage for the laser moves with a threaded shaft. The purpose is to keep time with the advance of the recorded data. The whole mechanism is jumping back and forth erratically for a few seconds. Then briefly the CD will work correctly followed by more erratic movement. Left alone this jerking and momentary playing will continue for thirty to forty minutes. After this period the CD unit will play normally until the whole unit is turned off for several hours. Is this a circuit problem or a mechanical problem with the player itself? What would cause either problem. If it is mechanical, can the CD player be fixed or, if not can I buy a replacement? If it is a circuit problem, what approach to debug the circuit controlling the CD operation could you suggest?
"Since this unit “works” as expected after a warm-up period,I would first look for any poor solder connections around the motor control IC. If I recall correctly, there should be two ICs marked BA6209 or BA6219 (most common for units of this vintage) that are the motor drivers. When playing a CD, there are two movements that take place to provide continual reading of the disc. First is the lens itself that changes angle to read the track (fine movement) followed by the motor rotating the shaft to physically move the optics assembly (gross movement). Both of these happen somewhat simultaneously to give a smooth movement overall to read the disc in a spiral fashion.
From what you are describing, the CD system gets lost and the gross movement from one end to the other over the disc is to locate its last position from which it will continue. This can happen for a few reasons. I suspect that the gross movement is not controlled correctly which is causing the optics to overshoot the track. When this happens, the system will “re-calibrate” by going to each extreme and then locate the correct track. Since this seems to recover and stop happening once the unit has been working for a while, either there are poor connections at the control IC or the IC is defective. Try re-soldering the connections first. If that does not resolve the problem, replace the driver IC and try again. Update this with the results.