Two CDM2 repaired

Since the CDM2 from the donor Philips CD150 is not working properly – if has problem to jump to tracks, especially track 7or higher – I had to prepare another spare part. 

The CDM2 from the second donor CD150 was working fine and I just replaced all the capacitors. Inside the CD150 I got a CDM2/10 and a CDM2/29. Seems there are a lot of different releases.

However, the CDM2 from the unit itself was not working and I really wanted to fix it. Not wondering anymore because everything in this sound machine was broken. By the end of the day it is getting more clear that someone already tried to repair it…

A first time repair with absolutely no knowledge of the drive. The datasheet (can be found in the download section) provides complex check routines with laser replacement etc.

So what is the issue with the drive:

• The motor does not spin or spins at extreme high speed
• The head moves up and down in light-speed
• When pressing play also two very strong buzzing sounds appear
• All together results into horrible noises

The first thing I already did some time ago was to replace all the capacitors. Of course this does not solved anything but was necessary anyway. In a second step I put all the chips on sockets. I bought some spare chips at eBay, they are still easy to get.

Next step was to check all diodes and transistors which were all fine. After checking the supply for the chips I began to replace them. Finally I noticed that the replacement of the TDA5709P showed some positive effects on the motor drive. The head is still not working but the hall motor is now working.

Another point which can be found quite often after a short research is the fact, that there is a small design flaw on the bracket of the flex cable. The plastic lock that holds the flex cable in place is pressing with two small points against the cable an the wires inside get broken. So I checked them and have notices that the contacts are defective. I repaired them by using a cutter to remove the first layer and soldered them together. Well, it does not look very professional (can something like this even look like professional?) but it does its job.

Since I do not want to let this happen again I drew another lock made of flexible filament with a slightly different design. It might also not be perfect but it keeps the flex cable in position and the head can move freely. The cad file can be found in the download section.

So everything should be fine now – but the CDM2 is still not working. Whilst the head is now not jumping from one side to the other, after pressing play there are still two buzzing sounds. I followed the datasheet and have done some measurements and all seemed to be fine. After a couple of minutes I noticed the buzzing sounds only appears when trying to jump to a track. Following the sound I located it – it was the focus of the laser. The laser should be visible when you look at it from the side. Better not locking into it directly, but there was no light. The measurement of the voltage on resistor 3106 showed no real result. The potentiometer for the power of the laser should be resulting into 50mV on resistor 3106. I had some thoughts and fears to use the potentiometer and to destroy the laser but I gave it a try.

I powered off the device and checked the position of the potentiometer. The datasheet points out to move it into the middle position when changing the head and laser unit so I thought this would be a good start. And what was the result? Someone already used the potentiometer and (thankfully) moved it down so the laser was too weak to read anything. That was the reason why the device tried to focus but had no chance to read the CD. I powered the device on and moved the potentiometer slightly until the laser was strong enough to read the disc and tadaaa – another CMD2 is working perfectly.