Sony D-321 focus coil not working

m_saborio

Hello forum!

I come back to you looking for help. As the title says, the focus coil of my D321 suddenly stopped working. The lens on the laser assembly stopped moving up and down. It moves just a little bit (it just sinks half a millimeter perhaps), but definitively not as much as it should. Hence, I assume that the player is unable to focus on the CD and read it. The problem happened from one day to the other: two days ago it worked like a charm, yesterday it stopped reading CDs completely. The palyer as not plugged to the wall nor to any other device. Hence "dead by over-voltage from the wall" is highly improbable.

I've tried the usual troubleshooting without success:

- Electrolytic capacitors are all replaced, specially the ones related to / on the traces providing power to the focus coil driver IC.
- The problem happens both with AC and battery power.
- I also checked the laser. It emits and its current values are healthy.
- The sled moves back and forth without issues. The spindle motor is also healthy.
- There is nothing blocking the lens from moving up and down.. It can move freely.
- I ran the tests described in the service manual. The automatic tracking and focus adjustment do not work because, well, the lens is not moving and hence no adjustment can be made. The tracking adjustment throws no errors, it just keeps trying to adjust the tracking to no success.
- The manual states that VCC should be between 3.2 and 3.25 V. I am reading 3.19V . Close enough I guess? AFAIK there are no potentiometers to adjust VCC. Therefore I would assume the value is OK.
- Inspecting the laser assembly, I found nothing unusual. The focus coils seem OK. I have not tested for continuity on the coils.
- I might have a replacement laser on my ''donors bin'', but I would like to discard any other possible root causes before switching the laser assembly.

Any ideas or suggestions are deeply appreciated. I really enjoy this player. I got it a couple of months ago and it is in mint condition.

m_saborio

I just tested the player with another laser, and the symptoms are exactly the same. Hence, I am fairly sure that the laser assembly is not the problem. Could it be something related to the driver? Oddly enough, the spindle and sled motors are both driver by the same driver, and both of them work without issues. Any ideas?

m_saborio

Another clue to the puzzle: the focus coils are pulling the lens away from the CD surface, but not towards it. So I tried using the player upside down, and to my surprise it worked again! On this orientation, the lens is pulled down by gravity (closer to the CD) and the coil pulls it up (away from the CD). Still, the question is then why the coils are working only in one direction? I checked all traces and found no damages at all. So I suspect that the driver (MPC17A38VM) is somehow defective?

m_saborio

with the help on some folks at stereo2go. I managed to find the problem. It has to do with a trace corroded by a capacitor (C528). The trace is right next to the capacitor pad and connects the cap to the motor/coil driver on the other side. When corroded, the part of the driver responsible for the focus coil losses power and stops working. All credit to Jorge at stereo2go: https://stereo2go.com/forums/threads/sony-d-321-focus-coil-not-working.10694/