Case History: Sony CDP-C215 will not load

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Sony CDP-C215 5-Disc CD Player
David Wise
September 2019
Salvation Army, $5


1. Won't retract drawer. If pushed in manually, won't load disc.

Sticky-intermittent; that is, once we fail, we never retract again until
power is cycled. At power-on, it retracts, chucks, spins, and plays.
Seems like the bad thing can happen during play - you can eject but
sometimes it won't retract afterwards.

While it's refusing, it still turns the carousel when OPEN/CLOSE is pressed
or when the drawer is pushed in manually, so the OPEN switch is working and
the cam/belt/motor/driver/micro are all okay.

When it's working it usually keeps working if you exercise it continuously.
When it sits for a while (including play), it fails again.

Could it be the UP or DOWN switches? The loading motor stops
when the drawer is fully in, so I think DOWN is okay. That leaves UP, which
is supposed to close when the disc is chucked, so it would have to be shorting.

Unlikely. I'll focus on power supply and general board cleanliness
and integrity. Look for bad solder joints.

10 Sep: I cleaned the UP/OPEN switches (shot of polyphenyl ether), no change.
I removed and replaced the flat cable between the main board and the BD board, no change.
I resoldered both connectors the flat cable plugs into, no change.

But I'm getting warm.
The sled LIMIT switch S101 was noisy. Cleaning it didn't help, but I discovered that
manually cranking the sled out away from TOC gets the machine out of the broken state.
The instant LIMIT opens, the motor relaxes and we're golden again.

15 Sep: I'm monitoring sled motor and LIMIT. (The former with a zero-center analog
Differential Voltmeter, the latter with an Audio Signal Tracer.) Cleaning may not
have helped at first, but the failure rate has gone down and I can't reproduce it
on command anymore.

I discovered that in the failing state, the sled is hard against the inner stop
and still being driven inward at full power. When I manually cranked outward from
TOC (which opens LIMIT), the runaway motor drive ceased and the machine resumed working.

16-18 Sep: Can't reproduce. Signal tracer emits a clean click on LIMIT transition.
19 Sep: Reproduced a couple times. Exercised LIMIT by alternately hitting PLAY and STOP,
and it cleaned up. Watch.

22 Sep: Preemptive strike. Added a one-pole RC lowpass filter between S101 LIMIT and
IC101 focus/tracking/sled chip.
10K and 10nF. We can get away with this because the MOS IC inputs draw no current.
(1) Wire a 3.3K pulldown resistor between S101 and Gnd (this will replace R109);
(2) Cut the trace between S101 and the via;
(3) Wire a 10K resistor across the cut trace (this grounds the IC input);
(4) Remove R109;
(5) Wire a 10nF cap across the R109 pads.
Doing it in this order avoids floating the IC101 pin and ESD risk.
Now there is a 100us time constant on close and 133us on open.
The sled will stop slightly closer to the spindle, but apparently
the head is still in the TOC because it works.
22 Sep through 2 Oct: Can't reproduce.
FIXED. I think.

CAUSE (speculative)
Noise on LIMIT closing is getting past debounce mechanism, and wedging
the microcontroller into a loop where it is commanding Sled In.
The condition is cleared when LIMIT opens.
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