"Mark Zacharias" wrote in message
...
"N_Cook" wrote in message
...
Neither me or owner will spend out on a new optical unit (failed laser),
big spondulics. But a near industry standard KSS 213C looked somewhat
similar , so I tried it out. This one laying around , unknown condition,
from some scrapped something. The ribbon feed lines for the 3 laser pins
matched , the other 2 deck motor+switch leads matched up, so tried it
out. Laser lit but logic of the end stops wrong so swapped the optical
unit across to the original (scrapper would not have mechanically fitted
in the Denon anyway). Required some bodging to fit, straightforward but
too much for detailing here, but sledge etc worked .
Adjusted power pot and cleaned lens and now consistently reads data track
and plays about first 2 minutes track1 of any CD I try, faulters and
stops, will not play any track 2 or higher.
I suspect the registration of the centre limit switch is out, but could
be a problem with the rack although powers up and down the slide without
incident with only 2 volt on the motor, but I will try marking rack and
cog of the 2minute stoppages. I assume a new (cheap) KSS 213 would show
the same stoppage.
So how to adjust the end stop , ? pieces of shim material added and
subtracted in the gap between sledge and leaf switch and suck it and see?
or some other problem likely?


I think this is a sled motor issue; I have never seen any limit switch
other than the inner (start) switch. As the tracking coil reaches it's
physical limit, a player will skip or "falter and stop" just like you
describe, if the sled does not advance.Check the voltage across the sled
motor as this process unfolds. At some point the voltage should increase
to kick the sled forward. Maybe there's a mechanical obstruction, maybe
you still have wiring issues.

Mark Z.


I would agree with everything that Mark says. The lens tracks across the
disc with a sort of 'wave' motion, the 'fine' part of this process being
handled by the lens tracking coils, and the 'coarse' part by the sled motor
and associated gearing. The time between motor 'roll-ons' varies from player
to player, but is typically between about 4 and 10 seconds. If you monitor
the voltage across the motor during each period, you will see it ramp up
gently until the point is reached where the motor rolls over one or two
commutator segments. If all is well with the servo, the motor and the
mechanics, there should be no overshoot, but often there is, and the motor
will roll back a little. When I am looking for this specific problem, I
always mark some radial lines on the large top-side drive gear with a
Sharpie pen. You can then watch the behaviour of the coarse tracking
operation, doing a rough count between roll-ons. If you see the time varying
a lot, there is usually a mechanical problem with either the motor or gear
train. If you see it taking a long time to roll on round about where you are
expecting it to give trouble, you can try helping it along by giving the
gear a gentle poke in the direction it should move. If that keeps it
playing, then there you go. Maybe the sled motor on the original deck is
poor. You could always try the old trick of squirting a drop of switch
cleaner in the holes at the back, and then 'blasting' it very briefly
several times in each direction with 12 volts. That will usually clean up
the comm and brush gear enough to get it running smoothly again, proving the
point that you need to replace the motor.

You might also check the performance of the spindle motor, as this can also
cause tracking problems if it produces enough data jitter. Also, try
selecting a track well into the disc, before pressing play, and see if it
goes there ok and plays through the track, or gives trouble again a couple
of minutes in. 'Lumpy' spindle motors tend to behave better on later tracks
where the rotation speed is less. Looking at the eye pattern on a scope can
tell you a lot about tracking and jitter behaviour. The same 'clean it and
blast it' technique can also be used on spindle motors to temporarily
recover them to prove the point

Arfa