Hello all,
I'm trying to fix (and understand!) my long served and well beloved 1988 vintage Philips CD350 player, which uses a CDM-2 drive.
The problem is a severe difficulty in acquiring lock of the radial servo. It makes horrible noises while it struggles to read the TOC, and most of the time it fails and gives up. It's a bit worse with some disks than with others. IF the player manages to acquire radial servo lock, it then easily reads the TOC and plays the disk without any further trouble.
It's sensitive to the position of the player. Placing it on an inclined surface seems to help. It also acquires lock more easily if I try to send it to a position further out on the disk, like track 3 or higher, while it is still trying to acquire lock and read the TOC. I guess it somehoe manages to read the TOC, piece by piece, even while not having managed to lock in the radial servo.
When trying in service mode, focus acquisition is perfect. Manually moving the arm by the fast forward and back keys works perfect too, the motor startup works well, but in service position 3, where it switches on the radial servo, the problem starts.
Scoping the radial servo and focus servo outputs shows that the focus is fine at all times, very close to zero DC, with assorted noises of about 0.5V p-p on it. The radial servo instead goes rail-to-rail with all kinds of huge noise and spikes while it tries in vane to lock in and read the TOC. If it manages to lock in and start working, it shows a sine wave of roughly 5V p-p and about 800Hz, on which about 0.5V of noise is riding. I can also see a small amount of a low frequency sine, showing disk eccentricity, which is normal.
Now this big sine wave is what has me intrigued. I guess it's coming from the nominally 650Hz oscillator in the TDA5709 radial error processor. But what's the purpose of this??? Can anybody enlighten me why Philips put an oscillator there to put that strong, relatively high frequency signal on the radial motor, together with the actual control signal? This looks almost like the high frequency bias of tape recording, but I still can't fully figure out its purpose.
And of course, any hint about what could be the problem with my player would be welcome! It has always, since new, been a bit temperamental, refusing to read some disks, but now a few days ago it got much worse, quite suddenly.
Interestingly it reads CD-R's no worse than pressed CDs, despite having been manufactured before CD-R's were invented.
The laser and optics seem to be fine, as the nominal 50mV between test points 1 and 2 reads 51.4mV, showing an almost perfectly accurate total photodiode current.
The only adjustment on this unit is the laser power output, and that one is obviously fine, so I didn't touch it.
I checked the electrolytic caps on the CDM-2's board for capacitance and ESR, finding two that had a somewhat high ESR (33uF at the laser supply, and a 47uF supply bypass cap, measuring about 6-8 ohm ESR each). I replaced these two. No change in behavior.
I know, I know... I should toss it and get a new player! But that's just against my most beloved principles! So if anybody can help me, both with the player's problem and with the purpose of that 650Hz oscillator, that would be most welcome!
Manfred
I'm trying to fix (and understand!) my long served and well beloved 1988 vintage Philips CD350 player, which uses a CDM-2 drive.
The problem is a severe difficulty in acquiring lock of the radial servo. It makes horrible noises while it struggles to read the TOC, and most of the time it fails and gives up. It's a bit worse with some disks than with others. IF the player manages to acquire radial servo lock, it then easily reads the TOC and plays the disk without any further trouble.
It's sensitive to the position of the player. Placing it on an inclined surface seems to help. It also acquires lock more easily if I try to send it to a position further out on the disk, like track 3 or higher, while it is still trying to acquire lock and read the TOC. I guess it somehoe manages to read the TOC, piece by piece, even while not having managed to lock in the radial servo.
When trying in service mode, focus acquisition is perfect. Manually moving the arm by the fast forward and back keys works perfect too, the motor startup works well, but in service position 3, where it switches on the radial servo, the problem starts.
Scoping the radial servo and focus servo outputs shows that the focus is fine at all times, very close to zero DC, with assorted noises of about 0.5V p-p on it. The radial servo instead goes rail-to-rail with all kinds of huge noise and spikes while it tries in vane to lock in and read the TOC. If it manages to lock in and start working, it shows a sine wave of roughly 5V p-p and about 800Hz, on which about 0.5V of noise is riding. I can also see a small amount of a low frequency sine, showing disk eccentricity, which is normal.
Now this big sine wave is what has me intrigued. I guess it's coming from the nominally 650Hz oscillator in the TDA5709 radial error processor. But what's the purpose of this??? Can anybody enlighten me why Philips put an oscillator there to put that strong, relatively high frequency signal on the radial motor, together with the actual control signal? This looks almost like the high frequency bias of tape recording, but I still can't fully figure out its purpose.
And of course, any hint about what could be the problem with my player would be welcome! It has always, since new, been a bit temperamental, refusing to read some disks, but now a few days ago it got much worse, quite suddenly.
Interestingly it reads CD-R's no worse than pressed CDs, despite having been manufactured before CD-R's were invented.
The laser and optics seem to be fine, as the nominal 50mV between test points 1 and 2 reads 51.4mV, showing an almost perfectly accurate total photodiode current.
The only adjustment on this unit is the laser power output, and that one is obviously fine, so I didn't touch it.
I checked the electrolytic caps on the CDM-2's board for capacitance and ESR, finding two that had a somewhat high ESR (33uF at the laser supply, and a 47uF supply bypass cap, measuring about 6-8 ohm ESR each). I replaced these two. No change in behavior.
I know, I know... I should toss it and get a new player! But that's just against my most beloved principles! So if anybody can help me, both with the player's problem and with the purpose of that 650Hz oscillator, that would be most welcome!
Manfred
Hi,
I had exactly the same problem many years ago with CD460 using this mech.
After many hours of deduction and testing, I discovered that the main swing arm bearing had hardened grease.
At the time, I had no service info but was able with extreme care, to release, clean, relubricate the bearing and set it all back up again. I never had any more trouble from it.
The AC sine you are seeing is normal drive of the dynamic motor. It is described in the service doc for the CDM-2 mechanism available here.
PHILIPS CDM-2 CD-MECHANISM SM Service Manual free download, schematics, eeprom, repair info for electronics
This manual is de-facto on the full range of that mech and it's many variants and grades.
Hope this helps
Dave
I had exactly the same problem many years ago with CD460 using this mech.
After many hours of deduction and testing, I discovered that the main swing arm bearing had hardened grease.
At the time, I had no service info but was able with extreme care, to release, clean, relubricate the bearing and set it all back up again. I never had any more trouble from it.
The AC sine you are seeing is normal drive of the dynamic motor. It is described in the service doc for the CDM-2 mechanism available here.
PHILIPS CDM-2 CD-MECHANISM SM Service Manual free download, schematics, eeprom, repair info for electronics
This manual is de-facto on the full range of that mech and it's many variants and grades.
Hope this helps
Dave
Hi Dave,
you were right! This morning I disassembled the mechanism, originally just with the idea of adjusting the perpendicularity between the laser and the disc, as described in the service manual. For that I had to remove the flex bearing holder plate, to break the tabs that disallow alignment. There I noticed the bearings had sticky lubricant, and the lower one also had some dirt in it. I cleaned the bearings (the balls and both cups of each bearing), and re-lubricated with some high quality camera oil I have on hand, since I do not have 100,000 CST silicone oil, as required by the manual. I don't know how long this camera oil will work, but perhaps I can find silicone oil for the next time I have to do this!
After reassembly and alignment of the perpendicularity, the player works fine!
Now of course I can't be sure if the problem was because of the stiff and dirty lubricant, or because of disalignment of the laser perpendicularity. But I think it was indeed the lubricant, because the alignment was still within the tolerance specs given in the manual, even if pretty much at the limit of that tolerance.
In any case, the arm moved quite easily even before relubing it. The force required to move it was at most about one third of what the manual gives as limit. But yes, it was a little bit sticky in the area closest to the center of the disc.
But my curiosity about the 650 Hz oscillator in the radial servo continues. The service manual you say, which I downloaded two days ago, doesn't tell anything about it, except for showing it in the diagram. I tend to think that its purpose may be swinging the signals up and down inside the dynamic range of the chip, to make the AGC circuit act well before hard, continuous saturation, but that's a little far-fetched... Another possibility is that this signal is intended to vibrate the arm, very slightly, with an amplitude far less than the CD track width, to keep it from binding, based on the principle that dynamic friction is alwaus smaller than static friction. But this is also a bit far-fetched! If this was the purpose of the oscillator, a much simpler circuit would suffice.
So the player is fixed, but I'm still looking out for an explanation about that oscillator in the TDA5709!
Manfred
you were right! This morning I disassembled the mechanism, originally just with the idea of adjusting the perpendicularity between the laser and the disc, as described in the service manual. For that I had to remove the flex bearing holder plate, to break the tabs that disallow alignment. There I noticed the bearings had sticky lubricant, and the lower one also had some dirt in it. I cleaned the bearings (the balls and both cups of each bearing), and re-lubricated with some high quality camera oil I have on hand, since I do not have 100,000 CST silicone oil, as required by the manual. I don't know how long this camera oil will work, but perhaps I can find silicone oil for the next time I have to do this!
After reassembly and alignment of the perpendicularity, the player works fine!
Now of course I can't be sure if the problem was because of the stiff and dirty lubricant, or because of disalignment of the laser perpendicularity. But I think it was indeed the lubricant, because the alignment was still within the tolerance specs given in the manual, even if pretty much at the limit of that tolerance.
In any case, the arm moved quite easily even before relubing it. The force required to move it was at most about one third of what the manual gives as limit. But yes, it was a little bit sticky in the area closest to the center of the disc.
But my curiosity about the 650 Hz oscillator in the radial servo continues. The service manual you say, which I downloaded two days ago, doesn't tell anything about it, except for showing it in the diagram. I tend to think that its purpose may be swinging the signals up and down inside the dynamic range of the chip, to make the AGC circuit act well before hard, continuous saturation, but that's a little far-fetched... Another possibility is that this signal is intended to vibrate the arm, very slightly, with an amplitude far less than the CD track width, to keep it from binding, based on the principle that dynamic friction is alwaus smaller than static friction. But this is also a bit far-fetched! If this was the purpose of the oscillator, a much simpler circuit would suffice.
So the player is fixed, but I'm still looking out for an explanation about that oscillator in the TDA5709!
Manfred
The 650Hz signal is used to automatically adjust the tracking gain. It is injected in the tracking servo and the tracking gain is adjusted to get a fixed amplitude (or phase shift – I'm not completely sure about this after 30 years …) of the 650Hz component of the tracking error signal. Because the original 650Hz signal and the 650Hz component of the tracking error error signal have exactly the same frequency, this is done easily using a lock-in (synchronous) detector.
Philips used this smart technique from the beginning (CDM-0).
Philips used this smart technique from the beginning (CDM-0).
Thanks, that's it! With that info I was able to google more sources and finally find a Philips patent that covers this circuit, with an explanation complete enough to understand it - at least for the most part!
patentimages.storage.googleapis.com/pdfs/US4471477.pdf
I can only admire these people who came up with such solutions!
Manfred
patentimages.storage.googleapis.com/pdfs/US4471477.pdf
I can only admire these people who came up with such solutions!
Manfred
Hi Manfred,
You will almost certainly find that the camera oil, although likely a fine oil, will gum over fairly short period of time. I fully recommend sourcing a fine silicon based lube asap.
If memory serves, this is the grade of lube I bought (10CS) grade.
Esslinger.com Pure Silicone Watch Oil
And never had any problem for the 10 or so years I had the player.
Personally, having worked in a production environment, producing TV's and other audio gear, I would NEVER assume that the unit was assembled with precision and care, it is rarely the case in consumer grade manufacturing where speed and efficiency are paramount. What I am saying is that, it is very possible your machine was over oiled or contaminated during assembly; it is also probable that fine adjustment was not accurately performed.
You've guessed it - I don't go with the theory that everything is made to spec because I have experience of the opposite.....cynical me !!!
You will almost certainly find that the camera oil, although likely a fine oil, will gum over fairly short period of time. I fully recommend sourcing a fine silicon based lube asap.
If memory serves, this is the grade of lube I bought (10CS) grade.
Esslinger.com Pure Silicone Watch Oil
And never had any problem for the 10 or so years I had the player.
Personally, having worked in a production environment, producing TV's and other audio gear, I would NEVER assume that the unit was assembled with precision and care, it is rarely the case in consumer grade manufacturing where speed and efficiency are paramount. What I am saying is that, it is very possible your machine was over oiled or contaminated during assembly; it is also probable that fine adjustment was not accurately performed.
You've guessed it - I don't go with the theory that everything is made to spec because I have experience of the opposite.....cynical me !!!
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