CDM2/10 Behaving Badly

[Dave S]

I have Cambridge Audio CD2 which uses the CDM2/10 mech.

When the CDP is cold it will not read discs, however once the player starts to warm up, maybe 10 minutes after being plugged in, the player gets consistently more reliable at reading discs. When the player is fully warmed up it rarely fails to read a CD and plays with almost zero errors showing on the disc fault LED. When fully warmed up the player will read some CDRs (will read TDK Speed-X CD-R80 but not Thats CDR-80TY Super Cyanine II), however the disc fault light is almost permanently on during playing of CDRs.

When the player fails to read the disc the motor does one of two things:
a) spins clockwise for about 1/3 of a revolution and then runs up to medium speed anticlockwise for about 2 seconds.
b) spins clockwise possibly up to full speed for about 2 seconds and then runs up to full speed anticlockwise for about 3 seconds.

Any ideas what is wrong and how to fix it?

Anyone got a service manual for the Cambridge CD2?

Thanks,

Dave

[zygibajt]

First I would exchange all electrolitics.
Second clean all the laser's conecting film joints.
Third adjust laser with two adjusting pots.

Bartek

[Dave S]

Here's how I got on.....

First I would exchange all electrolitics.

Done: 5 Electrolytics on the CDM2 pcb have been changed to Pana FC. All the parts removed measured OK and the replacements made no difference to the performance.

Second clean all the laser's connecting film joints.

Done.


Third adjust laser with two adjusting pots.

There are two pots:
1K near to the TDA5708 (photo diode processor)
22K near to L272 ( dual power op-amp)

I assume the 1K pot adjusts the laser power and the 22K adjusts the tracking in some way. I have cautiously tweaked these, after measuring the resistance with a DVM. The 22K pot seems to reduce the measured resistance whichever way it was turned, turning CCW made the tracking worse and CW made either no change or a marginal improvement - eventually I set it a tiny fraction of turn CW from the starting point.

The 1K pot had a more noticeable effect:
Original setting was 284R
297R made things much worse
220R was better
Eventually settled on 243R as the CDP played CDs faultlessly and seemed to find tracks quickly. It still really struggles to play CDRs though.

Have I turned the laser power up or down?
Is the laser near to dying or is there some other problem?
Where can I attach my scope to check the eye pattern?

Dave

[zygibajt]

Have I turned the laser power up or down?

I think you turned it up.But by changing all electrolitics I meant all of them in the CD player ,especially near motor and laser servo chips.If the player works very good when is warmed up and doesn't when it's cold the chances are you have some bad solder joint or dried electrolitic cap near the laser or motor servo chips.
The laser lens might be still in very good condition.But it also can be dying,too,especially if it doesn't read CDRs.There are some cheap players with CDM2/10 ,that you can buy for a couple of Euro on eBay and get the spare laser.If it turns out that your laser is dying,let me know I will tell you the ones.

Bartek

[Dave S]

Hi Bartek,

I replaced all 5 of the the electrolytics on the CDM2 pcb - this is where the motor and servo chips are located.

After the tweaks the CDP is now mostly reliable from cold with CDs. With CDRs the player struggles irrespective of whether it is warm or cold and on the odd occassion when it does play a CRD the error LED is almost permanently on.

A friend of mine has a CD2 and his plays CDs perfectly. With CDRs it sounds fine but the error LED lights frequently (maybe his laser is tired but not quite as bad as mine?).

Yes, it would certainly be useful to know other players with CDM2/10 inside so that I can keep an eye out for them.

Thanks,

Dave

[guido]

Hi,

Have a cdm2 manual, doesn't say which version

1k is indeed laser adjust, no 22k pot in my manual (?)
The 272 is used for radial motor and focus motor, so could be both.

To adjust laser:
- insert disc without defects
- connect voltage meter (DC) over resistor of 4k7.
- play track 1 of a good cd
- adjust to 50mV +- 5mV (measure over resistor, NOT to gnd).

This 4k7 resistor is connected to vcc on one side and a 100k resistor and a cap on the other side. cap 47n goes to -5V, 100k resistor goes to flex foil pen 5 and 330pF cap. this 330pF cap goes to pen3 (HFin) of TDA5708.

So find TDA5708 pen3, the 330pF cap, the 100k resistor and then the 4k7 to vcc. So this is at the receiving end and not near the pot.

My cd650 has CDM2/29, the manual is different. This has the MAB controller on-board, where in the 650 this servo microprocessor is on the main pcb.

Good luck,

[Dave S]

Thanks for the excellent instructions Guido!

The flex pinout is different on my machine but the other bits seem the same - anyway I managed to find the 4K7.

The player reads CDs but not CDRs with 66mV across the 4K7, any less than this and it will not read CDs.
It seems pretty clear that the laser is near the end of its life.

At least I know what's going on now!

Cheers,

Dave

[guido]

Originally posted by Dave S
Thanks for the excellent instructions Guido!

The flex pinout is different on my machine but the other bits seem the same - anyway I managed to find the 4K7.

The player reads CDs but not CDRs with 66mV across the 4K7, any less than this and it will not read CDs.
It seems pretty clear that the laser is near the end of its life.

At least I know what's going on now!

Cheers,

Dave

Mmm, dont think so. I'm not an expert here, but:
You are measuring at the input side. So you can crank up the laser way enough, since you are over 50mV. Also the receivers in the laser head are ok, again you are over 50mV.

So my guess would be the TDA receiver chip or the cap between those resistors and the input pin.

Try replacing some caps around the TDA, might be worth a try for some pennies.

[Dave S]

You are measuring at the input side.

Yes this is logical but since TDA5708 seems to completely unavailable I decided not to spend more time messing with this.

I decided to try another method, I borrowed 2 CD2s from a friend of mine. One of them has CDM4/11 (lucky sod!) which tracks anything and everything - just like my 3 Arcams with CDM4/X. The other has CDM2/10 which behaves in exactly the same manner as mine.

Jean-Paul knows!!!! He said many times to avoid CDM2 and buy CDM4!!!

I have seen CDM 4/11 available at UK£95 +VAT
CDM4/31 is more like £43 + VAT.
The only difference I can see is the 6 way connector for the tray drive, which is easily sorted.
Any reason why CDM4/31 would not fit/work?

Dave

[guido]

Hi,

A 4/31 should (!) be a drop-in for a 2/29. I posted on this before, got a 2/29 in a cd650 and a spare 4/31 for it but never tried.

My 650 plays anything, no problems at all. Both transports come with the TDA's on a pcb underneith, but without the servo microcontroller (which is on the main pcb). The manual i have is from a third type of cdm2, now with microcontroller on the attached pcb.

The 2/29 has a hall motor, the 4/31 doesnt ('toy' motor) iirc (don't have them around). So a 4/31 is useless for you, i think. Since the electronics are on the attached pcb, it does not matter that the motor is a different type. The 7210 doesn't mind

A 4/11 is only the transport, no pcb. Got one of those for 5 euro, player still attached Also a hall motor btw.

Dont know cd2/10, but i guess now it is like the 4/11, no pcb and hall motor. Which leads to the conclusion that if you swap only the transport and not the electronics for 4/11, and it works, that my previous thoughts are wrong

So best solution; find yourself a player with 4/11. Like i said, 5 euro for an aristona. And you get the TDA's for free