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Everything is perfect - still my CDM-1 does not work!
Everything is perfect - still my CDM-1 does not work!
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Old 22nd December 2017, 09:32 PM   #1
Salar is offline Salar  Germany
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Default Everything is perfect - still my CDM-1 does not work!

At the beginning, some important note: I have two payers with CDM-1 units.
Some time ago I had big problems with one payer. After long search (and doing the basic repairs like resoldering parts and ground plane connections, recapping etc.)
I found that one cap had a short to ground. Repaired this and the player worked like charm.
Later I developed a way do do a swing arm alignment which is more precise
than being done by the book:

Philips CDM-1 swing arm alignment

But half a year later, this CDM-1 fails again. It will read a CD sometimes but stop after some seconds. Amplitude of eyepattern seems o.k.
As I wrote in the beginning, i have two identical players. So I was able to swap the CDM-1 between players and also swap the boards on the CDM-1 itself.
No change but I assume a defect in the electronics can be excluded by now.

But there is no mechanical defect visible:
The arm swings free, no cracks in the flexible cable visible, clean lens, disc motor is ok.

Any ideas?

All the best, Salar
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Old 24th December 2017, 03:06 PM   #2
phildela is offline phildela  England
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I have serviced quite a few CDM1 based players and the most common fault is with the Turntable height, the teflon nut wears down and this changes the height (laser to disk) enough to cause reading problems. If you have adjusted it in the past, you need to ensure the grub screw is locked in position (I use nail varnish). Just bought a battered Marantz CD-74 from eBay which read nothing, and it took me an hour to guess the alignment close enough to start reading.
I see you already changed the electrolytics on the CDM1 boards, you should be able to see the red laser by looking from the side (not directly at it). I have also had tracking problems due to a failing SAA7020 on the Decoder PCB as well.
Merry Christmas,
Phil
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Old 24th December 2017, 03:15 PM   #3
anatech is offline anatech  Canada
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Everything is perfect - still my CDM-1 does not work!
Hi Salar,
What does the quality of the eye pattern look like?

Early CDM-1 lasers can have the suspension for the lens sag. That means that you can set the grub screw high enough to read, but it won't play. Get it down and it won't read, but if it does the tracking will be perfect. The only solution in that instance is to replace the transport assy. I've had this happen with some Revox and Studer CD players. It is frustrating.

-Chris
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Old 24th December 2017, 06:49 PM   #4
Salar is offline Salar  Germany
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Hi Chris,
nice to hear from you - it has been a long time- and Merry Xmas!
Could you describe the lens sag more specific.?
There is just one blade, damped with black tape.
Now, I did all those things Phil suggested aleady half a year ago,
even bought paint to secure the the bottom bearing that adjusts table height.
BTW it is the G-Revision with brushless motor, seems to be very common, in a Philips CD-304MKII and in a CD-104

I think - but I have to remeasure - that on one occasion, when the CDM-1 caught the track, the eyepattern was clean and instantly blurred. So I am not sure whether it was the probe or the CDM-1.

As I wrote before, I am able to swap every circuit board, including the disc motor (Laser Power has to be very carefully aligned before the swap - very interesting that the boards need a very different aligment. Variable resistors can differ by half a turn) It must be the mechanics. I did oil the ballbearing half a year ago but this was a very thin lubricant especially for bearings.

What about the "wobble" against friction. Any way to inject it - and observe the mechanical movement?
Again, the arm moves free...
All the best,
Salar
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Old 25th December 2017, 03:26 AM   #5
anatech is offline anatech  Canada
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Everything is perfect - still my CDM-1 does not work!
Hi Salar,
And a Merry Christmas to you too sir!

The alignment jig injects a tone into the servos and the monitor points create a lissajous pattern on the oscilloscope. You can see if there is excess friction with the head, especially if it is not even. The pattern would appear to be distorted. I do the same thing to check loudspeakers. Woofers, midranges and tweeters will all show distorted patterns if the suspension isn't smooth and linear - ish. Nothing's perfect. The lens actuator is basically like a tweeter with the exception that it will move in another axis as well. The head is free to move in restricted 2 dimensions.

The suspension of the head determines the starting point for the search for a disc (reflective surface). If you are outside that range, it will not lock to the surface of the disc. Once it does lock, you have a certain vertical range the lens can track the head over. You can "bottom out" high or low if the suspension has sagged. It's been years since I have set the tracking and focus gains on a Philips, Studer or Revox machine. But let's just say the procedure is memorable if you are dealing with a head that has sagged. Once properly set up, these transports tend to lock up and track very well. But, like any other transport, there are some defects it can't handle that transports like the Sony does very well, and vice-versa. You use Philips test disc 5 for setting the gains.

-Chris
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Old 26th December 2017, 11:41 PM   #6
Salar is offline Salar  Germany
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Hi Chris,
thanks for the detailed explanation! I can dig further into
the problem in January. I can look it up myself but I assume
I need a rig, no service mode to check the wobble?
Thanks a lot,
Salar
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Old 27th December 2017, 03:00 AM   #7
anatech is offline anatech  Canada
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Everything is perfect - still my CDM-1 does not work!
Hi Salar,
I'm trying to remember where the details of the jig were listed. I think it was in a mechanism manual, but it might have been in each model. They would give you the circuit. I made it into a circuit built in a box with a switch between focus and tracking. I discovered that if you just leave a jig as a board, they go missing and get destroyed often. As soon as it's in a box, it becomes mostly immune to those problems. I put the switch in to avoid changing wires around. This saved me a huge amount of time over the years.

-Chris
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Old 27th December 2017, 11:26 AM   #8
Salar is offline Salar  Germany
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I have the manuals and will look it up!
All the best!
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Old 27th December 2017, 02:31 PM   #9
anatech is offline anatech  Canada
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Everything is perfect - still my CDM-1 does not work!
Hi Salar,
It should be interesting. The socket was for the Nakamichi system timer.

-Chris
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