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NSM CD 3101 AC (CDM4 transport) does not play CD-Rs
NSM CD 3101 AC (CDM4 transport) does not play CD-Rs
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Old 21st May 2018, 03:08 PM   #1
derYeti is offline derYeti  Germany
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Default NSM CD 3101 AC (CDM4 transport) does not play CD-Rs

I recently bought a NSM CD 3101 AC disc changer which cannot play CD-Rs, only the original pressed Audio CDs. I have a second unit of the same model and so far it could play any type of CD. So something must be wrong with my new CD changer.

The CD changer has a Philips CDM4/53 transport and TDA8900, SAA7310 and SAA7321 ICs on the servo PCB. I found a service manual (incomplete) for the player and could upload the servo PCB schematic if needed.

What I did so far to solve the problem:
  • Cleaning the lens of CDM4 with IPA
  • Replacing all the electrolytics on the servo PCB
  • Checked the 3600 pF Polystyrene capacitor as suggested in another thread
  • Checked the BC338 output transistor for the laser power supply

Those above mentioned steps were not successful. Somehow I think that the problem is related to the servo PCB but I really don't know what I should do next. Any help is highly appreciated.
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Old 26th May 2018, 07:02 AM   #2
derYeti is offline derYeti  Germany
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Please find attached the schematic.

I forgot to mention that I checked the power supply as well. I could measure all expected voltage levels for the different supply rails.

I replaced all electrolytic caps with low ESR types of the same value except the bipolar 680 nF capacitor 2025 for the radial drive supply. I replaced that with a foil type capacitor. Do you think that the low ESR value of the replacement caps could cause a problem? I read in another thread that in some cases a higher ESR cap could be beneficial.
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File Type: jpg NSM_CD_3101_AC_servo_PCB_schematic.jpg (1.01 MB, 98 views)
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Old 26th May 2018, 07:14 AM   #3
Mooly is offline Mooly  United Kingdom
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NSM CD 3101 AC (CDM4 transport) does not play CD-Rs
Here's what I would do.

As you have another similar model I would begin by looking at the RF level on a scope and compare the good and bad unit. Do that on a normal disc.

Are they similar in amplitude and quality ?

Now put your CDR in the good player and see whether the amplitude and quality of signal is similar to the normal disc.

There are a lot of variables with CDR and some players cope better than others. So you need to do some initial measurements with a scope to see what is going on and whether the RF amplitudes are correct or marginal.
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Old 26th May 2018, 08:17 AM   #4
derYeti is offline derYeti  Germany
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Thanks a lot for the suggestion. I will try to do that. It will be difficult because I have no idea yet how to access the servo PCB with the probes while playing a CD.

Do I need to measure at point 17 in the schematic (HF out, close to TDA8900 pin)?
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Old 26th May 2018, 08:32 AM   #5
Mooly is offline Mooly  United Kingdom
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NSM CD 3101 AC (CDM4 transport) does not play CD-Rs
Yes, point 17 or point 65 on the SAA7310, whichever is easiest to get to.
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Old 26th May 2018, 11:05 AM   #6
derYeti is offline derYeti  Germany
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As the bad unit was already on my work bench, I started measuring the eye pattern from that with an original pressed CD:
It showed +2V DC offset and an amplitude of 0.75V. I think the amplitude is on the lower side for a CDM4. The signal looked clean.

I try to capture and upload an image later. I will test the good unit as well.
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Old 26th May 2018, 11:07 AM   #7
Mooly is offline Mooly  United Kingdom
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NSM CD 3101 AC (CDM4 transport) does not play CD-Rs
The AC amplitude sounds low. I would have expected around 1.2 volts peak to peak.
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Old 26th May 2018, 11:36 AM   #8
derYeti is offline derYeti  Germany
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Do you mean 1.2V amplitude or peak-to-peak voltage?
I measured the AC amplitude, so actually my peak-to-peak voltage would be 2*0.75V = 1.5V.
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Old 26th May 2018, 11:45 AM   #9
Mooly is offline Mooly  United Kingdom
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NSM CD 3101 AC (CDM4 transport) does not play CD-Rs
Like this. I would have thought around 1.2 volts from top to bottom for a Philips RAFOC. The signal will be sat on top of any DC voltage present but that is normal.

1.5 volts sounds a bit high but don't alter anything, just compare it with the good one using the same disc and measurement points. This picture shows 1 volt peak to peak.
Attached Images
File Type: jpg Capture.JPG (59.6 KB, 87 views)
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Old 27th May 2018, 05:01 PM   #10
derYeti is offline derYeti  Germany
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I managed to capture the eye patterns:
  • Good player - original CD - 1.3Vpp
  • Good player - copied CD - 1.3Vpp
  • Bad player - original CD - 1.3Vpp
To me those eye patterns look pretty much similar. What can we conclude from the results?
Attached Images
File Type: jpg Bad-player-original-CD-1.3Vpp.jpg (183.8 KB, 80 views)
File Type: jpg Good-player-copied-CD-1.3Vpp.jpg (166.8 KB, 80 views)
File Type: jpg Good-player-original-CD-1.3Vpp.jpg (179.7 KB, 81 views)
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