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 Post subject: [MDP-600] Won’t spin backwards (counter-clockwise)
PostPosted: 24 Sep 2023, 15:27 
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I’m getting into the weeds of this Sony power supply to try to figure out what component(s) are bad and preventing the spindle motor from going in reverse. The unit plays fine on Side A, but can’t play Side B if it can’t spin the other way. It also affects Side A operations because motor reverse is also used for slowing the disc down. Therefore, pressing Stop ultimately causes an error because the disc doesn’t slow down fast enough, and the player gives up.

I have two of these units, and so I have two of everything to swap out. Both power supplies exhibit the same behavior. I re-cap’ed one of them. I’m in the process of removing transistors and checking them, but so far they check out fine. The other has an op-amp with a blown-out hole in the middle. Replacement op-amps are on the way.

I thought I’d post here in case someone else diagnosed a similar issue with a Sony.

Thanks,
Adam
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 Post subject: Re: [MDP-600] won’t spin backwards (counter-clockwise)
PostPosted: 24 Sep 2023, 16:01 
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Sony players are not too common here, not too many if anybody has experience
fixing them.

Once in a while there are some like yourself who possibly had luck fixing them but no techs to my knowledge can fix them.
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 Post subject: Re: [MDP-600] won’t spin backwards (counter-clockwise)  Topic is solved
PostPosted: 27 Sep 2023, 14:35 
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I found the offending component. I realize I may be talking to myself here since I’m working on a Sony, but this same push-pull circuitry might be in the other brand players as well. Even if you don’t have a dual-sided player, the motor still needs to brake to slow down the disc. Applying the “brakes” is biasing the motor in reverse temporarily.

The circuit diagrams in the service manual are tremendously helpful. The positive motor lead measured around 13V. The negative lead measured -13V while spinning up for Side A. For Side B, the negative lead went positive, but the positive lead never went negative. That narrowed down where to look. Oddly enough, it wasn’t a power transistor but instead a switching transistor that biases the power transistors on the motor positive lead. Q55 is a PNP transistor. It passed the base-to-collect and base-emitter tests, but showed leakage from C to E. Active components rarely fail unless the passive components (capacitors) fail. This power supply was full of bad, leaking capacitors.

The PNP transistor is a 2SA1309A, but it looks like many other PNP will substitute. I used a power transistor from a donor power supply, and it works.
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 Post subject: Re: [MDP-600] won’t spin backwards (counter-clockwise)
PostPosted: 27 Sep 2023, 14:49 
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Glad to hear you fixed it, with Pioneer players we have a bunch of people who post who have fixed them, not so many with sony's.
Also a lot of repair manuals for Pio's not sony's.

All info is great to have, I'm no tech just know what I've read and who has had luck repairing stuff.
While Sony players are not known to be great for LD, any working player is great to have for the format.
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