I’m working on this nice Sony system from the early 90’s at the moment, the faults found were the tape decks not working and the cd player wouldn’t read a disc.
Starting on the tape deck it was the usual thing of the belts turning to goo, so a good clean up and new belts sorted that out.
The cd player was much more of a challenge, the tray would open but not close, to get it to close I had to turn it off and then on again, then it would load the disc but wouldn’t read it. I decided to sort the loading out first and investigated the two switches that tell the microprocessor when the tray is open or closed, one of them read 70 ohms across the contacts where it should read zero ohms, that needed dealing with but the switch was sealed, the only way to clean it was to make a hole in the plastic casing so I could get a sliver of emery paper in there, once that was sorted the tray still wouldn’t close so I decided to move on to the problem of it not reading discs, I noticed that as the mechanism loaded to the point where it would try to focus on the disc there was no movement of the laser, it should rise and fall as it tries to focus, also there was no tell tale red light emitting from the laser. So I started looking at voltages, all were present and correct, I moved on to the laser board itself, checking voltages on the microprocessor, and operation of the door switches, all seemed fine…then I noticed the limit switch, it’s there to tell the micro when the laser is in position to read the disc, I had assumed this was working because the laser was moving up and down on the sled motor and was stopping when the switch was closed…as it should, but I just thought I’d measure the resistance across it to be on the safe side, well, 500 ohms across it, once again it should be zero ohms, same sealed switch as the tray switches and the same procedure to clean it, it was very difficult to get to for removal from the panel, I’ve circled it in one of the photos, and even more difficult to get back in but once it was the laser came to life and the tray opened and closed on the button. The resistance across the contacts had been enough to confuse the micro, but it didn’t end there, even though it was now trying to focus it still wouldn’t read a disc, a new laser assembly was required for that to happen, so everything was stripped, cleaned and lubricated, reassembled with the new laser and it sounded superb.
