CDM1 Mk.II wear indicators?

[tonyptony]

I took a chance and bought a CD player with a Mk.II drive that had been advertised as having relatively few hours on it (I sort of know the seller so I had a little bit of faith in the report). I'm planning to pull the cover off to take a look at the transport. I have read that the CDM1 had that teflon bearing plate that would sort of get a depression in it after long use, but is there anything on the Mk.II I could look at to give me an order of magnitude sense of how much time is on it?

[stephensank]

Without a digital voltmeter and a laser power meter, the only way to tell if a mkII has had a lot of use is if these two things are true: 1)It has trouble reading some or all cd-r's or any cd's, and 2) Adjusting the bottom platter motor thrust bearing in an upward direction cures the problem.
However, needing to adjust that bearing, other than belts, is all I have ever seen go wrong with a cdm1-mkII. I have never, ever seen a laser even get weak on one.

[tonyptony]

Thanks Steve. I do eventually plan to check the laser current (if I have the instructions right I need to check the voltage across the 12 Ohm resistor near the data cable on the servo board). Can I do that while keeping the drive installed? From the drawings it looks like the servo panel is under the drive mechanism. Not sure how I'd get flea sized hook probes across a resistor if it's under the drive.

As to the teflon plate and the deck height, what should the deck height be? I have a CD880 service manual, but it's in Dutch.

[stephensank]

I have found no better way to adjust the platter thrust bearing than to simply finely tweak it until it has no trouble playing Memorex cd-r's(or your own favorite worst cd-r).
And, yes, most often the only practical way to do laser current is to solder a couple of temporary test wires to run out from under the unit. Be sure, though, to adjust using a wide variety of discs, shooting for the best average. Otherwise, it will only play well made discs. But there is no need to even do the adjustment if it has no trouble playing any discs after platter bearing adjust. Can't remember the last time I actually found the need to adjust current on anything older than a CDM-4.

[oshifis]

Originally Posted by tonyptony

As to the teflon plate and the deck height, what should the deck height be?

I followed this method: measure the voltage at the focus amplifier output and adjust the screw on the 1st track until it reads 0 mV. Repeat on the last track, then on the first track, find a compromise. Use a Torx screwdriver and apply a small drop of paint at the side of the screw when finished.

[tonyptony]

Thanks guys.

oshifis, I have the schematics for my unit, but could you provide a location or pin number for this measurement? Also does the screw adjustment need bottom access to the unit?

I've read that some on mechanisms adjusting the deck height can throw the deck "out of parallel" and that some tweaking is needed to make sure it stays flat. Is the Mk.II one of these types?

I've also heard that with servo boards this old (close to 20 years) it's a good idea to replace all the electrolytic caps. True?

[oshifis]

I adjusted the turntable height on my old Marantz CD-74, there is a test point for this purpose. There must be the same test point (other end of the wire) on the CDM-1 servo board, but not easily accessible. I piled a lot of books on either side of the player so that I could access the screw from under.
I just heard that the 33 uF axial electrolytic capacitors (there are 5 of them) tend to fail; fortunately I had no issue so far.

I have the CDM-1 service manual in Dutch. It seems difficult but I suppose the adjustments are for factory and need to be done only once. There is a visual adjustment (turntable height and parallelism) and an electrical adjustment (laser current) using a special test jig.

[tonyptony]

Originally Posted by oshifis

There is a visual adjustment (turntable height and parallelism) and an electrical adjustment (laser current) using a special test jig.

That's the part that worries me. When you tweaked the screw for the height adjustment how easy did it look to throw out the parallelism?

[musicomputer]

I think that there's some confusion in this thread.

CDM1 and CDM1mkII are completeley different from each other. The CDM1mkII is effectively a diecast version of the CDM4 and bares little resemblance to the CDM1. Indeed, CDM4 lasers can be easily fitted to the CDM1mkII to repair it (and I've seen weak/dead lasers on these mechs).

I see no adjustment screw for turntable height on the CDM1mkII, the only ways I can think of adjusting it is to either replace or shim the bearing, or break the glue holding the turntable to the spindle, move it up the shaft and then re-glue it (good luck with that ).

[tonyptony]

I really wish I had an English language version of the CD880 service manual I have.