Adjusting laser on CDM-1

[Thomas]

Having troubble reading some discs and after reading all the good advice in this thread here I have come to the conclution it might be necessary to up the laser output a bit.

The problem is the PCB in the CDM-1 is another version than showed in my service manual (Marantz CD73). The one showed in the manual has 2 pots and the one in my player got 3. Now I don't know which adjusts the laser output.

If anyone could tell me which pot it is I'd be verry happy. Also, which version is the 'newer' one?

I have drawn an outline of the PCB with the placement of the pots to make explaining easier.

[Netlist]

I can't tell you which pot to turn, but you might want to check the
LM337T in the PSU for bad solderings first, position 6105, as well as the other heat dissipating devices in that PSU.

/Hugo

[Thomas]

Originally posted by Netlist
I can't tell you which pot to turn, but you might want to check the
LM337T in the PSU for bad solderings first, position 6105, as well as the other heat dissipating devices in that PSU.

/Hugo

I Just resoldered the entire PSU the last week because the 8V rail was comming and going. But thanks anyway.

[Netlist]

Then I would carefully mark the 3 pots and while looking at the eye pattern, turn the pots one by one.

/Hugo

[EDUM]

Hello Thomas,
As I was "involved" in the development of this CDM I hope I can help you a bit.
The 47k potmeter is FOCUS OFFSET
The 2k2 potmeter is FOCUS GAIN
The 6k8 potmeter is LASER OUTPUT

The 6k8 potmeter differs depending on the used laserdiode. (in my docs it is 1k Ohm.

The Pcb shape you draw sugest a CDM-0 Pcb. CDM-1 Pcb's are more "squarish". I can imagine that Marantz used slightly different parts.

Be carefull with "adjustments". FOCUS OFFSET is indeed an adjustment. You have to set it correct, otherwise it influences the overall performance negatively. The FOCUS GAIN influences the "playability" behaviour. This a compromise. The tightness of this servoloop determines very much how a well a disc plays. Depending on the sort of errors that can occur on CD's the "best' adjustment can be a bit different. So this adjustment is indeed a compromise.The LASER OUTPUT determines indeed the power of the laser. Here simply enough is enough. There is no reason to shorten the lifespan of the laser with a StarWars "lightsaber" approach.

I sugest you contact the local service organisation for the correct servicedoc and servicedisc. I am affraid that the needed service disc is a bit pricy. On the other hand a CDM-1 was developped when there was not to much knowledge about disc behaviour, so it is a bit more muscular as you see today. It might be worthwhile.

I hope I helped you!

----WARD----

[Thomas]

Originally posted by EDUM
I hope I helped you!

----WARD----

You did.

Exelent answer, thanks a lot!