ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
I bought the CD 5500 new as part of a complete 5500 system in August 1988. It worked fine for many years but around 2015 it began to abort occasionally when playing the second or third track on certain CDs. By 2021 this had became too frequent and I decided to try to fix it.
I removed the case, lifted PCB5 into service position and, not having a proper replacement for C2103, I soldered a 10uF capacitor in parallel with the original. I also cleaned the lens with isopropanol. After that all the CDs I tried played perfectly, so thinking the problem was solved I screwed PCB5 back into position and refitted the case.
That’s when the problem with the tray started. Sometimes I’d press Open ready to play a CD and nothing would happen. Other times the tray would come out slowly to half-way and then shoot out to the end stop and leave the motor racing for a second or two. Just occasionally it would all work normally.
Eventually I realised the fault never happened when the PCB5 was in ‘service position’. After a lot of false trails I found that slight movement of the PCB caused intermittent breaks in the low voltage AC supplied from the mains transformer to the rectifiers feeding C3 and the +15 volt and +12 volt regulators.
The +12 volt supply is regulated by zener diode D2 and feeds quad op amp, IC5. Amplifier A4 in IC5 is part of a shaper that cleans up the pulses from opto-encoder, PE201, and sends them to the TRAY POSITION input of microcontroller, IC4. In this way the micro is able to sense the position of the CD tray, but only if the pulses are present.
What made diagnosis awkward is that the pulse shaper carries on working even when the +12 volt line has dropped to only a few volts. Because of the charge stored in C3, this takes several seconds to happen after the AC supply to the bridge fails. So although I could trigger the bad contact by moving PCB5 up and down slightly, the delay masked the connection with erratic tray movement.
Anyway the problem turned out to be a bad connection between tracks on PCB5 and the pins on multi-way connector P10. After I re-soldered all the pins of P10 the problem disappeared.
(Note: writing this in case it helps anyone else. It amplifies what I wrote in https://archivedforum2.beoworld.org/forums/p/49230/347247.aspx#347247).