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wierd optical sled behavior on Alpine car audio 6-disk CD changer

I have an Alpine CHM-S630 6-disk CD changer that is giving me grief.

The unit selects each CD properly from the magazine, but as soon as it loads it into place, the optical sled slams out to the full extent of the limits of the track, out to the extreme edge of the CD diameter. It never appears to go to the center of the CD, and it never takes a read from the disk.

After the sled hits the track limit, then for about 2 seconds, the worm & roller mechanism keeps trying to push the sled out through the side of the case, resulting in a horrible grinding noise as the plastic block on the sled strips itself against the "worm" screw, since the sled can't move any farther.

After about 2 seconds elapse, the unit gives up and stops trying to push the sled past the limit of the track. Another 2 seconds after that, the unit gives up on spinning the CD, and the CD comes to a halt.

This happens every time the unit loads a CD.

I've tried cleaning the lens on the sled, but it doesn't seem to be an optical problem. It doesn't seem to be a mechanical problem, either. The worm & roller for sled movement works just fine - the problem is that for some reason, the unit is telling the sled to slam out past the limits of its track. I'm stumped.

Can anyone point me in the right direction for a fix?

Thanks.

Reply to
trainor
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It sounds like the "home" switch or sensor is stuck or damaged, making the unit think the sled is stuck at the center of the disc and making it constantly try to move the laser away from the center. I would look for a broken switch or the tab that activates it. Good luck.

Reply to
Jumpster Jiver

Thanks for the idea.

I tested the "home" switch for the sled with my multimeter, dialed in to the 200K ohm setting. It's just an ordinary (tiny) spring-loaded two-position pin switch.

With the switch pressed in (ie. sled is at center of CD hub), I get no resistance (00.0 on the multimeter display). But with the switch released (ie. sled is anywhere *except* right at the center), I get a reading of 47.8 on the multimeter display. These results are both using the 200K scale setting on the ohmmeter.

I would have expected infinite resistance, not 47.8, with the switch released. So that's a bit surprising. The switch isn't perfectly open when the pin is released, although there's obviously much more resistance than when the pin is pressed in.

Do you think there is inadequate resistance with the switch released, or would 47.8 a normal result for this kind of switch?

I'd love the problem to be a bad switch, but Murphy's Law says I can't get off this easily.

Thanks.

Reply to
trainor

Did you disconnect the switch when you tested it? If not, then you are reading whatever it is connected to when it is open...

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Reply to
Dave Dunfield

You're right, I did not disconnect the switch before the test. So there's the reason that I don't get infinite resistance when it's open. Thanks.

So the implication is that the switch is working properly, I guess. I suppose I could desolder the switch and double check, but since I get

0 resistance when it's depressed, and the resistance increases when it's released, it appears to be working properly.

Anything else worth checking? I hate seeing this thing turn into an expensive paperweight.

Thanks.

Reply to
trainor

Hello,

While I don't know the Alpine car units at all, I've seen some Sony single disc home players do this when one of the clocks (oscillators) fails. If left there making that awful noise, it will damage the rack gear on the optical pick up, by grinding the teeth off it.

Seeing this will require powering the unit on a work bench with an oscilloscope, and probably a service manual. I don't work on car audio stuff myself.

Regards, Tim Schwartz Bristol Electronics

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Reply to
Tim Schwartz

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