I have a Marantz CD-74 on the bench. Initially, it would NOT read any CD. The platter would not turn at all. I tweaked the height adjustment screw and laser power pot just enough to get it to read a CD. Then, I worked through the adjustment section of the SM. There are only 4 adjustments called for -- Laser Output; Turntable Height; Radial DC-offset, and PLL Circuit adjustment. I do not have the Philips test CD, so I performed these adjustments over a handful of commercially pressed CDs, and the adjustments are all well within specs.
Now, the unit will play most CDs but not all. When it plays, the RF eye pattern looks reasonably good. It's about 1.2v PP, the eye is sharper on some CDs compared to others. Even on the ones it plays well, it takes a moment to start up. If you watch the eye pattern on start up, you can see that the machine takes two or three trys before it locks in and plays. I only tested with commercially pressed CDs.
I should mention that the CDs that it will not play, are fine on other players I have.
There are NO philips blue radial caps in the unit. The caps are all Elnas and test good in circuit with a Peak ESR meter. The power supply voltages are spot on.
Because of the effort at startup, I am starting to suspect that the Focus Offset or Focus Error Adjustment may need to be adjusted. These adjustments are not covered in the SM.
Does anyone know the adjustment procedure for these two pots on a CD-74 or CD-84? Since I finally have it playing some disks, I am very hesitant to change the settings of either of these without more information.
Alternatively, is there something else I should be considering given the above?
Now, the unit will play most CDs but not all. When it plays, the RF eye pattern looks reasonably good. It's about 1.2v PP, the eye is sharper on some CDs compared to others. Even on the ones it plays well, it takes a moment to start up. If you watch the eye pattern on start up, you can see that the machine takes two or three trys before it locks in and plays. I only tested with commercially pressed CDs.
I should mention that the CDs that it will not play, are fine on other players I have.
There are NO philips blue radial caps in the unit. The caps are all Elnas and test good in circuit with a Peak ESR meter. The power supply voltages are spot on.
Because of the effort at startup, I am starting to suspect that the Focus Offset or Focus Error Adjustment may need to be adjusted. These adjustments are not covered in the SM.
Does anyone know the adjustment procedure for these two pots on a CD-74 or CD-84? Since I finally have it playing some disks, I am very hesitant to change the settings of either of these without more information.
Alternatively, is there something else I should be considering given the above?
Attachments
Best you download the service manual for the 74. I gather it is possible to wing it without the test CD. The uP (in service mode) tells you what needs adjusting and the manual tells you the node to monitor when making each adjustment.
Hello, I know the Focus Offset calibration method:
https://www.diyaudio.com/community/threads/purpose-of-focus-offset-trimpot-on-cdm-1.398289/
But I would say, the trimmer is fixed by a paint drop, and the factory setting is good.
The Focus Gain calibration is described in the Service Manual of the Philips C.D.M.-1 drive. But that adjustment is not critical, either.
I recommend to disassemble the turntable motor, pull out the long axle (there is a retaining ring), clean it and wipe it with sewing machine oil very sparsely. The supporting plastic torx screw should also be grinded flat on a fine sandpaper. I finish its surface on a piece of copy paper until it becomes shiny. Then add a little silicone oil or light silicone grease. The electrical focus offset should be nulled after reassembly. Check on a couple of factory CDs, at the beginning and at the outer track, and find a compromise.
https://www.diyaudio.com/community/threads/purpose-of-focus-offset-trimpot-on-cdm-1.398289/
But I would say, the trimmer is fixed by a paint drop, and the factory setting is good.
The Focus Gain calibration is described in the Service Manual of the Philips C.D.M.-1 drive. But that adjustment is not critical, either.
I recommend to disassemble the turntable motor, pull out the long axle (there is a retaining ring), clean it and wipe it with sewing machine oil very sparsely. The supporting plastic torx screw should also be grinded flat on a fine sandpaper. I finish its surface on a piece of copy paper until it becomes shiny. Then add a little silicone oil or light silicone grease. The electrical focus offset should be nulled after reassembly. Check on a couple of factory CDs, at the beginning and at the outer track, and find a compromise.
"The electrical focus offset should be nulled after reassembly" - by turning the Torx screw, not the Focus Offset trimmer.
I have a similar situation on desk with one of my CD-67 players - some disks play, some don't, some play sometimes.
The factory disks play always, the self burnt ones some play and some do not and some play sometimes.
So I bought a CD-43 as a test rig and the measurements showed that the eye pattern amplitude was ca 1,3V on factory disks and ca 35% less on the self burnt disks that did not play (well). Service manual expected 1,7V.
Lucky me, the signal path had a two transistor amplifier section:
and by changing the first stage resistors (after simulating the effect in LTspice) I added "modest" 15...20% gain to the stage (not nearly enough to meet the SM amplitude) and that was enough to make the player play all the CD-s I currently have. Should I run into some unreadable disks then the gain can be increased. No side effects so far.
Long story short - your CD-74 seems to have enough components in the signal path where the gain can be modified (unlike CD-67) - so instead of attempting to change the adjustments by the book why not just increase signal amplification?
You need to do a full simulation on the signal path, play around with component values and see what change provides the best result.
I have not owned that player so unfortunately I am not going to do the full work for you 🙂
That’s okay. I’m generally more interested in getting things working like when they left the factory. Thanks for the suggestion, though.
Sorry, due to laser chain deterioration due to age I have dropped that goal long ago 🙂
So I do not mind changing "two resistors" ...
I noticed, without having a technical explanation, that some Philips and Marantz CD players became sensitive to the thickness of the disc.
Measure the thickness of the discs that work and those that do not work with a digital caliper and draw conclusions.
Measure the thickness of the discs that work and those that do not work with a digital caliper and draw conclusions.
Looking into the schematics, this seems to be the area where to search for potential gain increase:
Actually the photodiode signal is pre-amplified by a thin-film integrated circuit on the cdm-1 mechanism. Then it goes directly to the Q501 PLL. The left side of the drawing is the drop-out detector that controls muting below a certain HF signal level.