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Old 1st October 2003, 08:05 PM   #1
Thomas is offline Thomas  Denmark
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Default Adjusting laser on CDM-1

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.
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File Type: jpg cdm-1.jpg (8.6 KB, 987 views)
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Old 1st October 2003, 08:28 PM   #2
Netlist is offline Netlist  Belgium
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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
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Old 1st October 2003, 08:49 PM   #3
Thomas is offline Thomas  Denmark
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Quote:
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.
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Old 2nd October 2003, 06:31 AM   #4
Netlist is offline Netlist  Belgium
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Then I would carefully mark the 3 pots and while looking at the eye pattern, turn the pots one by one.

/Hugo
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Old 2nd October 2003, 09:01 AM   #5
EDUM is offline EDUM  Netherlands
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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----
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Old 2nd October 2003, 12:49 PM   #6
Thomas is offline Thomas  Denmark
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Quote:
Originally posted by EDUM
I hope I helped you!

----WARD----
You did.

Exelent answer, thanks a lot!
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Old 28th February 2017, 04:33 PM   #7
Salar is offline Salar  Germany
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Hi,
I do not find any detailed imformation how to observe foxus offset or
focus gain in any of the service manuals, i.e CDM-1, CD-100, CD-104. CD-304.
CD-304MKII. In the Service manual of CD-304MKII there is an addenumt in German that the Focus offset can be observed measuring the Eyepattern via an
AC-voltmeter - seems to be completely wrong. No difference at all, also
there is no change visible in the Eyepattern. You find graphics of the Signals but there is no naming for what they stand for.

So where do I find a focus offset signal?
All the best,
Salar
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Old 1st March 2017, 10:45 AM   #8
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Hi Salar,

It is player specific, because the focus servo is on a separate board.

I think it can be adjusted only by breaking the focus loop. In the CD-94 MkII service manual the J203 on the servo PCB should be disconnected, and turn on the laser by sorting pin A17/2 to GND.

My guess is:

- Play a disc
- set FO potentiometer to mid position
- adjust platter height until TP14 = 0V (uA741 pin 6)
- close focus loop and adjust FO until TP14 = 0

Might not be correct, I did not try it. EDUM could correct, I hope
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Old 13th March 2017, 02:05 PM   #9
Salar is offline Salar  Germany
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Hi lcsaszar,
you were talking about the 47k potmeter focus offset, werent you?

Anyway, I cant put the player into service mode right now - I will use the transport and pcbs in a DIY Player with new design .
This forced me to cut away parts of the display PCB and therefor some buttons to fit into the new design.
Thought it would make no harm, because in some players I know, service loops can be also accessed using the remote.
But with Philips (at last this model) , service mode does not work using the remote.
No time in the moment to rewire the missing switches on the VFD-board to make service loop accessible again.

I tried 2k2 focus gain while watching the eyepattern. I wonder if the correct description for this pot would be focus / tracking gain.
Because turning it anti-clockwise, youll hear a ticking coming up.
Turing it clockwise would make an audible hiss louder, but I noticed no difference. The his is focus gain in Sony-Players.
Turning the pot clockwise (Focus?) will make the laser lose tracking. Turning it anti-clockwise shows loss of tracking only if a disc with defects is played.
Thus I adjusted the pot by ear, listening very close to the CDM-1.
I turned the pot until the ticking just became audible.
After doing so I found out that I exactly hit the mid-position of the 2.2 potmeter "Focus gain" - not only by eye but also by checking the pot with a voltmeter..

So I hope there is a way to adjust the 47k "Focus offset" just by playing a disc, maybe with artificial defects. I adjusted the table height but I do not remember the procedure in the moment, did this some weeks ago...
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Old 20th March 2017, 09:26 PM   #10
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The alignment should be done in the following order:
1. Adjusting the laser current
2. Adjusting the height of the disc
3. Radial offset alignment
4. Radial control power amplifier adjustment (in service mode)

To adjust No.3, set the rig as on the attached picture and play a CD with no errors. You will want to obtain the minimum amplitude modulation with the trimpot 3158 on PREAMPL+LASER BOARD.
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File Type: png Screen Shot 2017-03-20 at 22.00.06.png (29.4 KB, 59 views)

Last edited by Willi Studer; 20th March 2017 at 09:46 PM.
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