Hi there,
This is a nice piece of semi-portable CD player from the 80's with excellent sound (PCM60P DAC). The US version is D-50. My problem is that it jumps occasionally at various points, every few minutes. The laser shakes and hits the disc for a second, then it plays again normally. The player can play written CDs, but the jumping occurs with factory CDs, as well. I have the service manual and adjusted it as accurate as possible. The laser is KSS-165A. Nominal laser current (written on the laser block) would be 49.7mA, I measured 54.6mA. According to the SM it should be within +5/-11mA, so I believe it is within the limits. Also the eye pattern amplitude is OK. I adjusted the Focus gain and Tracking gain so that the low frequency envelope modulation just disappears on the top of the eye pattern. I adjusted the Tracking balance for maximum cleanest eye signal. The SM writes about equal +/- spikes at the TE test point in pause mode, but this method did not work for me for some reason. As for the jumping, I cleaned the worm gear, and the laser head travels smoothly end-to-end as can be tested in service mode. Of course, I cleaned the laser lens. What else could cause jumping? What should I check? Could it be a bad component, like a dry electrolytic? Thanks in advance for any suggestion.
This is a nice piece of semi-portable CD player from the 80's with excellent sound (PCM60P DAC). The US version is D-50. My problem is that it jumps occasionally at various points, every few minutes. The laser shakes and hits the disc for a second, then it plays again normally. The player can play written CDs, but the jumping occurs with factory CDs, as well. I have the service manual and adjusted it as accurate as possible. The laser is KSS-165A. Nominal laser current (written on the laser block) would be 49.7mA, I measured 54.6mA. According to the SM it should be within +5/-11mA, so I believe it is within the limits. Also the eye pattern amplitude is OK. I adjusted the Focus gain and Tracking gain so that the low frequency envelope modulation just disappears on the top of the eye pattern. I adjusted the Tracking balance for maximum cleanest eye signal. The SM writes about equal +/- spikes at the TE test point in pause mode, but this method did not work for me for some reason. As for the jumping, I cleaned the worm gear, and the laser head travels smoothly end-to-end as can be tested in service mode. Of course, I cleaned the laser lens. What else could cause jumping? What should I check? Could it be a bad component, like a dry electrolytic? Thanks in advance for any suggestion.
Well, I replaced the spindle motor assembly, but it still skips occasionally. It is also sensitive to knocking the player gently with my finger. I readjusted the focus offset and tracking balance pots, but no improvement. Should I increase the laser current? This is the last thing I wanted to touch.
I noticed an interesting thing during the adjustment. When I play the 1 kHz square wave track of a recorded CD, sometimes there is no output, but the player runs as usual, display is OK, etc. The output signal returns when I knock the player. It looks as if the laser positions itself between two pits, not on the pits. But it plays other tracks well (apart from occassional skipping). What could be the reason?
Also I would be grateful if someone gave me any advice on properly adjusting the Tracking Balance. There are so many various methods on the net and I am really confused. I adjusted for the cleanest eye pattern, but there is no sharp optimum setting. I read somewhere that this is a super critical adjustment... TIA Laszlo
I noticed an interesting thing during the adjustment. When I play the 1 kHz square wave track of a recorded CD, sometimes there is no output, but the player runs as usual, display is OK, etc. The output signal returns when I knock the player. It looks as if the laser positions itself between two pits, not on the pits. But it plays other tracks well (apart from occassional skipping). What could be the reason?
Also I would be grateful if someone gave me any advice on properly adjusting the Tracking Balance. There are so many various methods on the net and I am really confused. I adjusted for the cleanest eye pattern, but there is no sharp optimum setting. I read somewhere that this is a super critical adjustment... TIA Laszlo
Is there no focus bias pot ? which would normally be adjusted for the clearest RF (Eyepattern).
As to the TE signal and equal plus and minus spikes.
What you have to do is set the scope on a slow timebase setting and look at the error waveform while performing track jumps. Keep searching from track 1 to the end of a disc and back and adjust so that it's symetrical above and below an imaginery line through the middle. Just thinking and going from memory... also try this adjustment while "music searching" as in hi speed search but not track jumps. It's many many years since I worked on these... and this playability complaint cropped up frequently.
As to the TE signal and equal plus and minus spikes.
What you have to do is set the scope on a slow timebase setting and look at the error waveform while performing track jumps. Keep searching from track 1 to the end of a disc and back and adjust so that it's symetrical above and below an imaginery line through the middle. Just thinking and going from memory... also try this adjustment while "music searching" as in hi speed search but not track jumps. It's many many years since I worked on these... and this playability complaint cropped up frequently.
Molly,
Thanks for your advices. I adjusted the baby yesterday very carefully. I found the best adjustment can be achived by watching the eye pattern. Focus bias and tracking bias could be set for cleanest eye pattern and maximum amplitude. The adjustment range is quite narrow, it is easy to find the best spot. Focus gain and tracking gain was adjusted by setting a lower timebase on the oscilloscope, monitoring the eye pattern envelope, and finding the point where a low frequency modulation on the envelope just disappears.
In spite of all these adjustments, there is still occasional skipping. When it happens, the laser nervously shakes itself, the worm gear turns to-fro, and finally it continues playing at the same point where it had before. Could it be some control circuit problem?
Thanks for your advices. I adjusted the baby yesterday very carefully. I found the best adjustment can be achived by watching the eye pattern. Focus bias and tracking bias could be set for cleanest eye pattern and maximum amplitude. The adjustment range is quite narrow, it is easy to find the best spot. Focus gain and tracking gain was adjusted by setting a lower timebase on the oscilloscope, monitoring the eye pattern envelope, and finding the point where a low frequency modulation on the envelope just disappears.
In spite of all these adjustments, there is still occasional skipping. When it happens, the laser nervously shakes itself, the worm gear turns to-fro, and finally it continues playing at the same point where it had before. Could it be some control circuit problem?
Impossible to diagnose at a distance...
Have you measured the tracking error voltage (DC level) while playing, and the voltage across the sled motor. If there is a mechanical problem the voltage will suddenly begin to rise without the sled turning, then suddenly friction is overcome and the sled jerks forward. I suppose it's possible that the pickup may have a problem. The "spindle" that the lens moves on can get "sticky" or perhaps the suspension has deteriorated. This was just a small flexible loop anchoring the lens assembly on the original D50 mk1 player although most KSS pickups are similar.
Have you measured the tracking error voltage (DC level) while playing, and the voltage across the sled motor. If there is a mechanical problem the voltage will suddenly begin to rise without the sled turning, then suddenly friction is overcome and the sled jerks forward. I suppose it's possible that the pickup may have a problem. The "spindle" that the lens moves on can get "sticky" or perhaps the suspension has deteriorated. This was just a small flexible loop anchoring the lens assembly on the original D50 mk1 player although most KSS pickups are similar.
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