Philips CDM-1 swing arm alignment

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One last thing: As I wrote earlier in this thread I did try to remove the lens to clean it beneath. It sits in a blade that is fixed horizontally by two screws.

Never do this!

Reason why I did it: I mistook the description of cleaning the lens of a CDM-1MKII for the CDM-1. Both are very different.:(
Played with the alignment of the blade tonight. This alignment is completely a matter of try and error.
You need to remove the cage with the tray, defeat the tray switch, take the tray´s clamper out of its mech.
You need a magnet to fix the clamper and CD on the disc table.
But after some trying I obtained a sharper and clearer eyepattern. Also amplitude did rise.
The blade is very fragile. Even gently pushing it with a screwdriver can bent its edges.
Again, this is an alignment that was better done at the factory back in 1983...
 
O.K, I think I found the solution for aligning the swingarm. No glass disc needed, no fluorescent tube, no mirror, no grid. Just a multimeter.
A scope would help as well but is not necessarily needed. But someone should confirm the following:

In the service manual´s chapter 4 "Mechanical Measurements and Adjustments " of all the players using CDM-0 and CDM-1, a resistor 3240 is mentioned.
It is on the main servo board (not on the CDM-0 / CDM-1 boards), and connected to the path leading to the focus motor of the swing arm.
This resistor connects to ground. Voltage measured across this resistor should be 0V - this means no offset in focus and correct turntable height.

But this means also: If the voltage is the same on the first track of a CD as on the last track, the swing arm is in perfect horizontal alignment.
And because horizontal alignment and tilt are related, tilt should be also zero.

Solder two wires to resistor 3240, measure the voltage on the first track and last track and adjust the swing arm´s plate until the voltages are almost identical.
I finally obtained around 8mV difference. Before it was more than 50mV.
You need to play with the plate´s screws a bit. Fastened enough for grip and still allowing movement. Again movement means fractions of a millimeter here.
I got to a point, where I even did not feel the plate moving with my fingers, but noticed the change on the multimeter.
A scope is for controlling sharpness of the eyepattern. But a sharp pattern should be a logical result anyway. Finally, the turntable height can be adjusted as well until 0V offset are obtained.

Finis - I hope!

How many different CDs did you use to align the swing arm? The reason I am asking is that there are large differences among different compact discs, not only in offset amount, but also in direction it goes - from plus to minus voltage and vice versa. Therefore, using only one compact disc is not enough. Attached is the screenshot of the table in which I measured and recorded offset data of randomly picked pressed discs from my shelf.

My description of the entire procedure, why you should use more different discs and how to calculate the mean value is described here:
http://www.diyaudio.com/forums/digi...ps-cdm-1-swing-arm-alignment.html#post4010679
 

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YEDS-18 from Sony. It was used by Sony for alignment. Because this disc is described as having tighter tolerances than normal, i assume it will not differ from discs from Philips made for the same purposes. I also expect warpness or bending to be low. Used "Digital Recordings" "CD-Check" for errors (highest level was passed) and again some CD-R for warping. CD-Rom are very flat. Still CD-R do not play well, eyepattern is very blurry. I also have a personal test disc, heavily scratched. (I "rescued" it from a demonstration player in a warehouse around 1984. The only theft in my whole live, but I could not to watch this nice
Jon and Vangelis Recording being further scratched by employees and customers to demonstrate the robustness of the medium) It has some defects on the data layer that make the Philips skip. Because i have some CDM-1 players on the shelf,
and tested it there as well I assume thst weak CD-R playback is common.
I have torepeat that I deliberately lowered laser output to 1V p-p as described in the service manual. I assume this value is even wrong, as I found the player originally having just below the common 1,2V p-p. But I want to save laser longetivity...
 
The CDM-1 which alignment I described in this thread ran perfect since then.
But in the last week playback detoriated very fast.
First scratched CD´s were not read just after two days, even the reference disc for
alignment YEDS-18 cannot be read. Sometimes, the player catches the first track
but will play with glitches and stop after 20-30 seconds. During this, aclattering Sound can be heard.
I first thought something must be grinding but the table, disc, lens and arm
are running free. The clattering or clicking sound must come from the impulses of the radial servo.
It does not seem to be 400bpm what one would expect from the clicking of a radial servos
with rotational speed on the first track. To me, it sounds more like 120 bpm or less.
Managed to attach a scope:
No change in the amplitude of the eyepattern thus I assume focus and laser are working.
But the eyepattern is very blurry. Disc Motor is strong an cannot be easily stopped with the finger
Voltages:
Not easy to measure. In stop mode, voltages for focus and radial servo seem to be ok.
I.e. I read positive voltages and their negative counterparts on the trannies.

Service manual is of no help, no real world measurements, just data of measurements in service mode

Anyone any idea what the problem might be?
All the best,
Salar
 
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Thanks for the reply!
The value is set to 1V-p-p as recommended in the service manual.
Trimpod was replaced before I did the mechanical alignment.
Where can I check a real world signal to the radial servo?
Almost all signals in the manual are based on injecting oscillated signals or monitored in service mode.
I assume it should swing equally around 0V with a perfect CD?
The clicking: Could it be that the servo tries to correct a drift caused by a missing motor signal?
 
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Your setting of 1Vpp (which I don't find anywhere in the manual) is 353mV, and I believe that this weak laser beam is the reason why the player cannot read out discs or track properly anymore.

Page 43 (number on page top is 7-11 / bottom Cs 5 229)
Position 65 A play: 1Vp-p. On the next page the 1Vp-p eyepattern is shown.

To me this is still very unlikely because the player worked fine for 8 weeks and then suddenly - almost over night - failed.
It also looks like the laser can keep focus but not track.

I did make a 10 minute break after writing the last sentence. I removed the bottom plate to check if I can move the laser by hand when it has catched track.
Normally you´ll have to use a little bit of force to kick the laser out of track with your finger. Wanted to check if tracking had become weaker.
To my surprise the player plays the disc well. But this has also happened in the days of the failure before
But I got used to some peculiarities of the player that have changed:
It takes half a second longer than before when the player goes from startup to play.
When I hit the Stop button, the laser will normally swing back into its resting position (middle of the arc) with a very unique hiss.
Dont know wether this is fading current from the servo circuit ore some injection from the mechanical assembly causes the hiss.
Anyway this shut-off hiss sounds different than before.

I might now sound like a delirious medicine man now,
but I remember that someone told me that some service technicians got so much used to the sound the laser mechs they were servicing so well so that they could adjust the gains just by their ears.
I would now say cold solder or dying Cap. I did not resolder every solder joint yet, just made the basic things like reworking connection points between ground planes...
But again, where do I measure the tracking signals - an what values should I expect?
All the best,
Salar
 
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Made further checks today:
A fine tracking signal for the radial servo seems to miss or is distorted.
It can be measured @ point 30, pin2 of IC6218.
In the service manual, this signal is not mentioned, a participant in a german forum pointed this out, the left picture shows how it
should look like, X = 2ms/div ; Y = 50mV/div.

What I see on my scope is shown in the right photo.

I also replaced the CDM-1 of the CD 304 with another CDM-1.
The problem persists, thus the fault should be on the servo board; parts of the DAC board process the servo signals as well.
 

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No idea what cause the ticking noise in a Philips CD 304MKII?

As I wrote I have two CDM-1 to check, both show the same fault.
It must be on the servo or decoder board.
In the meantime I did recap everything and swap voltage regulators.
No change. I did also take decoder and (for matching) digital filter and
DAC from a dead CD-160. No change.

Maybe I took a malfunctioning decoder to replace a malfunctioning decoder
- still waiting for a working Philips for a decent price on ebay to check this...

Working on a grounded bench btw.

I also started to replace the op-amps and transistors still available today.


The CD 304MKII will spin up and abort without seeking.

Sometimes it will seek with the ticking/nailing sound and abort.

Very, very rarely it will play for some minute with nailing/ticking sound, half-second mutes in the music and abort.

Still there is strength in the mechanism when I touch it in the rare occasion the disc is played.
The laser is not easy to move nor is the rotation easily to be stopped.

The symptoms described seem to be dependent from the state when the player is switched on. I checked the reset circuit it seems o.k.

Also pressing Stop on the player will do a reset anyway

ALL solder joints are soldered again, cabling is checked.

There is a constant current source BF550 feeding the decoder SAA7210 at pin 23.
The SAA7210 was very common in Philips/Marantz/Magnavox/Wadia players of those times. (Just like the Sony CX2035 types.)
It is used for the phase detector.

Something PLL-like?

The SAA7210 datasheet can be found here (PDF) SAA7210 Datasheet PDF Download - Decoder for compact disc digital audio system

Trying to measure the given voltage at pin 23 with a digital multimeter during play will make the laser jump.
This happened on the rare occasion when the Philips played a disc.

Is this behaviour normal?

Unfortunately the BF550 is not available at the local electronic shops.
I can only try a swap between the dead CD-160 and the CD 304MKII,
being forced to heat the sot-23 package of the BF550 during desoldering and resoldering.

After the swap behaviour did not change. But I do not know how likely it is that the BF550 gets fried anyway.

Any ideas what substitute can be used for testing?

What also seems to be interesting is that parts of the dropout detection circuit are placed on the tray board.
Not very well documented in the circuit diagram. Just the marking DO on a data line in the service manual gives a hint.

Pulling the cable between the servo boards dropout detection circuit and the the tray boards dropout detection circuit will
make the disk spin backward when the CD 304MKII is switched on.

I was able to swap the tray board between the CD 304MKII and a CD 104, both boards are identical, no change.

Unfortunately even though the servo boards of a CD 304MKII and CD 104 are almost identical, a swap for testing does not help because the controller IC is different.

In the attachment you will find a recording on how the CDM-1 sounds when trying to play a disc.
The first is the more common spin up without reading the TOC.
The second is the ticking sound when the player tries to read the TOC.
Maybe some experienced technician remembers these sounds and can point me in the right direction.

Again, the fault is NOT caused CDM-1 and it´s boards.
I have two CDM-1 with their own boards to check, both fail identically.
Lenses emit light, focus pulls up and down.

The CD 304MKII worked fine over 8 weeks of regular use after cleaning and alignment and did deteriorate within hours.

All the best,
Salar
 

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Hm - half a year later, the CDM-1 mentioned in this thread will not play -again.
Sometimes it will catch a track and then stop playing after some minute.
I had exactly the same symptoms before, but back then it was bad tantalums on the main servoboard.
Now the problem must be mechanical.

I have two players to check faults
and renewed all caps on one, also on the now defective CDM-1.

So I swapped the CDM-1 between both players to check circuitry and even swapped the boards on the CDM-1 itself.

Makes no difference.

Mechanically the arm moves freely, the spindle motor rotates freely, laser power ok, turntable height is o.k.
No signs of wear or cracks in the flex cables, focus blade seems to show the same stiffness on the broken CDM-1 as well as on the working CDM-1.

When the broken CDM-1 sometimes catches a track, all readings on a scope or voltmeter are well.
On the scope I once made the observation that the eyepattern suddenly jumps from clear to blurred.
But I can not tell whether this jump was caused by my scope or was a real measurement.

Any ideas? What about the wobble that is injected to overcome friction, can I observe it somehow?

Some other findings:

Could be that all electronic adjustments are due to tolerances of the circuitry on the CDM-1 board. Positions of the trimmers can vary heavily.
On one board the trimmer resistor for laser power was adjusted very high, more than half a turn than on the other board.
I reduced it before swapping boards and found out after swapping that i had to bring the trimmer back to almost the same position for getting the desired level.

In the english version of the CDM-1 service manual it is described that the
inner lens system can be removed from the arm (i.e for cleaning or replacing diode, probably without re-alignment)
using a #12 spanner by turning the tube of the lens-system anti-clockwise.
There are two ledges on the tube for doing so but visaully you won´t notice a gap or other hint that this is a removable part.

Did not work for me, I gave up after rather than breaking something.
 
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