Help with vintage Philips Cd Changer

[enryfox]

Hi, I'm Enrico from Italy and this is my first post in this forum. I like to repair stuff, mostly hi-fi units i pick-up from flea markets.

I recently picked-up a Philips CDC486 six discs changer from a flea market. Sound-wise it is a pretty standard Philips of its time with CDM 4/20 and TDA1543 as DAC. It appeared to have only mechanical problems and I tried to took care of that. Before embarking in the restoration, I tested if the CD player part was actually working and in service mode it successfully locked focus (phase 1), track (phase 2) and disc rotation (phase 3); after one minute it then started to play music and I was happy and started restoring it.

After stripping down, cleaning and fixing the cd-changer side, the player side appears to no longer works: on power on the disc spindle starts rotating at high speed and everything appears to be stuck. I am able to load disc and in that case disc rotation is slowed down and the pick-up seems to lock to the track, but there is no play back.

I tried again the service mode and this time I'm greeted with what is shown in the attached pic (note: the display works correctly in normal mode, so it is not a problem with the display or the main CPU itself)

Troubleshooting done so far:

All supply voltages are fine (+12, +/- 10, +/- 5); to fix the mechanical problem I had to basically disconnect everything; I suspected a bad connection, but the cd changer side "works" fine, the display is fine (when in normal mode), it is just the player section that is stuck.

I checked all grounding points (notorious problems in this old Philips boards), but being made with wires, they are fine, all pins that are supposed to be grounded are grounded. I re-touched all solder joints in IC's too, but behaviour has not changed.

I replaced three Philips caps (axial cyan coloured caps) which I know were bad (47 uF measuring on average 18 uF) but it did make no difference. Other electrolytic caps are from better brands and they are on power rails (which are fine).

The unit has two microProcessor, one controlling the disc changer side and another one controlling the CD player side. They both have a reset signal and it goes low on power on as expected. Then starts the anomaly: on the I2C bus connecting the two uC there is supposed to be activity, but instead both wires are "high" which is the start-up condition. The MUTE signal sent to the decoder IC SAA7210 is "high" while it should be "low". It basically seems the uP managing the CD player is stuck on start-up and does not continue.

I am out of options ... have I zapped an IC ?

[MathWizard]

Would there any buttons, switches or sensors that are stuck in the wrong position ? Then there's solder joint cracks that could be easily missed.

Any time I've tried fixing stuff with micro-controllers, usually the rest of the PCB seems fine, and it's just what the MCU is doing that I never figure out. And without a working model side by side to compare with, I get lost. Even if I have the schematic, the MCU is a blackbox, IDK enough programming to read anything inside them.


It would be easy to replace the MCU and try it, but then, is it worth the price, and it the chip real, and would it have all the program on it....so you might have to buy another working CD player, just to get a real chip.....I have mostly working CD player here too. IDK for sure if the MCU is the problem, but it sure seems like it.

[enryfox]

To answer to your last question, no, this CD changer is not worth investing any more money in it, beside the six disc changer is a pretty basic player, with a cheap DAC and a four digit backlight LCD display which can shown only track/index or elapsed time. And to be honest, having to use a six discs cartridge just to play a CD, it is not very friendly at all, it made sense back then when CD changers were common in car audio, but nowadays it is just a nuisance.

It is just the disappointment of having to give-up on a repair/restoration.

The service manual is of little use in case of logic problems, there is just indication to check voltages, reset, Clock and activity in the I2C bus; but if anything is wrong, there are no indication at all (I guess that would translate in "replace the board").

One aspect that puzzle me is where is the microcode stored: is it inside the microcontroller ? Is it programmable only once, is it an eeprom ?

One other failure that happened in other cases is the decoder chip SAA7210 which is interconnected with the uC managing the CD player side; I could try and change it, but again I do not think it is worth the money; if I found another player with compatible IC's, i guess this other player would be more valuable.

[Haenk]

The early Philips suffer from those axial caps - and from really bad solder joints. It's not uncommon to have a dozen bad joints, often hardly visible. I would check again.