Hello everyone!
Here is the scenario: Creek CD43 MkII player, with the obnoxious Philips CDM 12.1 mechanism. Reding and playing is erratic, skips, some discs -mostly CDR-s- not even recognized, etc. Well, this usually indicates a weakening laser head.
Then comes a brand new VAM 1202 (theoretically fully intercangeable) mechanism, and here is the twist:
With the new one, newer CDR-s and factory original discs rejected (laser starts, disc spins, then: "no disc"). BUT! Really old CDr-s with blue and green substrate material read and played flawlessly..... 😎 Seems like it can recognize only those 15-18 years old crappy written discs.
Any idea? Maybe too much RF output from the head amp? Unfortunately I cannot measure eye pattern because my scope is half dead.....😡
Also, service manual is unobtanium...
Here is the scenario: Creek CD43 MkII player, with the obnoxious Philips CDM 12.1 mechanism. Reding and playing is erratic, skips, some discs -mostly CDR-s- not even recognized, etc. Well, this usually indicates a weakening laser head.
Then comes a brand new VAM 1202 (theoretically fully intercangeable) mechanism, and here is the twist:
With the new one, newer CDR-s and factory original discs rejected (laser starts, disc spins, then: "no disc"). BUT! Really old CDr-s with blue and green substrate material read and played flawlessly..... 😎 Seems like it can recognize only those 15-18 years old crappy written discs.
Any idea? Maybe too much RF output from the head amp? Unfortunately I cannot measure eye pattern because my scope is half dead.....😡
Also, service manual is unobtanium...
I agree. A functional oscilloscope is necessary for this repair. Being able to measure the P-P amplitude of the RF signal is the key to resolving this. The old optical pickup probably doesn’t provide adequate RF signal amplitude. The new pickup might provide too much RF. But there’s no way to confirm this without the oscilloscope.
-EB
Thanks for your help, problem solved.... It was a faulty sled servo motor in the new mechanism. How? No idea, but when I put back the old motor in the new mechanism, it worked flawlessly. (so much for "original replacement part" 😱) Anyway, that particular model (CDM 12.1, VAM 1201-02 is plagued with many problems. In other words: cheap s...t)
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I’m tackling a faulty sled motor in a Sony CDP-C305 5-disc CD changer.
Its original sled motor has a partial short circuit, likely between 2 of its 3 commutator segments. This often prevents the sled from returning to the “home” position.
I offer several comments about this:
1) When the sled cannot return to the “home” position this causes the disc tray and carousel to behave quite oddly. Sometimes the tray won’t open. Other times the disc transport mechanism begins to oscillate up and down between the “disc clamped” (up) and unloaded (down) position. Power must be shut off to recover from this oscillating state. Evidently the MCU firmware cannot handle faults where the sled isn’t able to return to the “home” position.
2) If the sled is manually put into the “home” position first, then both the disc tray and the carousel function as they should.
3) When the sled is in the “home” position then this machine will initialize a disc and display the number of tracks and total playing time of the disc. But most of the time it cannot actually play the disc because that requires the sled to move.
4) Sometimes the sled will move sufficiently to play several seconds of the first track of a disc. In other words this sled motor is still “partially” functional.
At this point I decided to try an old trick to “temporarily” fix the faulty sled motor:
- I desoldered the sled and spindle motors from the servo PC board (in this machine they are soldered directly to the small servo PC board located underneath the transport mechanism). Then I moved the servo PC board far enough to disengage the motor terminals from the holes in the PC board.
- Then I removed one of the plastic sled drive gears to permit the motor to rotate freely without jamming the sled against its inner or outer limits.
- Next I connected a variable bench power supply directly to the sled motor. This particular motor is labeled “D/V 4.0V.” This indicates its “design voltage” is 4V.
- With the power supply current limit set to 500mA and the open-circuit voltage set to 4V, the motor did not rotate at all until I gave it a twist with my fingers.
- The current drain at 4V was nearly 500mA when the motor wasn’t rotating.
- After I manually gave it a spin, then it began to rotate slowly and the current dropped to 200mA.
- I gradually increased the voltage and suddenly it picked up speed and the current dropped to <100mA.
I don’t consider this to be a permanent repair.
But it did succeed at getting the sled motor to function well enough to play a disc for several hours in “repeat 1 disc” mode.
This confirms the optical pickup, spindle motor, and servo electronics are functional.
Next I will install a new sled motor.
-EB
Thanks for the info, it is very useful, and points out that in many similar cases not the laser is the culprit -as many believe- but other, mostly mechanism related problems. Reading and playing a CD is a very complex process, and requires all mechanical and electrical parts of the player work flawlessly together.