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Sony PS-LX520 Turntable Power Supply Fault

Hello all...

I recently cleaned up and restored to working order a Sony PS-LX520 linear tracking turntable. After that it played beautifully until two nights ago when I turned it on and found the "start" control to be unresponsive. As it turned out, the lights that normally come on to indicate speed and playback mode were also dead. It had been playing beautifully the night before.

The only sign of life was from the power button and the light bulb that is used to tell the turntable how big the record is. The table motor was trying to run, turning the platter very slowly. No part of the control panel works.

I popped it open and had a look inside to see if I could find anything obviously wrong. Nothing was obviously distressed. There are three different boards: one for audio, one for the logic control and a power/speed control board. Power comes into the unit from a multi-tapped transformer, and this seems to be OK. Markings on the logic circuit board seem to indicate that there should be -16 volts, +16 volts and +6 volts from the speed control/power board. I have the two sixteen volt supplies and they are very close to being dead on. The six volt supply is completely missing! Most of the connectors are point to point wiring, with the wires placed into plastic guides and soldered to the board. As they look difficult to remove, I have not attempted to see if something is loading down the +6 volt supply. Nothing is getting hot.

I have a service manual coming. Already I have been looking at the two filter capacitors on the power/speed control board. They are both 25 volt,

1000uF units. One holds its charge nicely and long after power off. The other one discharges much more quickly, but not quickly enough to make me think that a problem is draining it.

Every date code in the unit suggests it was made around the middle of 1987.

Has anyone worked on this turntable or a similar model and seen this problem?

William

Reply to
William R. Walsh
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Not sure it was this model, but they had some problems with 100uF 16 volt caps shorting on some of these and causing the problem you describe. Might have also opened an IC protector, IIRC.

Mark Z.

Reply to
Mark Zacharias

Hi!

Well, I was barking up the wrong tree at first. I replaced the two 25V

1000uF filter caps thinking that they weren't working properly. Oh well, now they'll definitely be good for some time to come.

As it happens, I found an open IC protector on the power/servo control board. After carefully examining the rest of the board and looking for any faults or shorts, I decided to cautiously jumper across the protector and see what would happen. The turntable control panel came to life, so I put a record on it. It would try to start and abort playback just before the tone arm would touch down. Hmmm.

That had me stopped for a bit until I thought about the bright light I was using to illuminate my work area. After turning it off, startup and playback of a record worked fine. I played a few hours worth of records with no ill effects. I definitely will replace the protector in the near future.

Now all I have to do is find a not-too-unreasonably priced source for the Rohm ICP-N10 circuit protector with small quantity availability. Digi-Key has a minimum order of some 3,000 (!!) units and while there are some on eBay, I really don't want to pay $5 shipping and gouging for items that would fit in a #10 envelope with tons of room to spare.

I am thinking that 23 years (!!) of on/off cycles and current inrush is what drove the little circuit protector to its breaking point. There are two inrush current limiters leading up to each filter cap on the power/servo board and my guess is that they ease the strain on the circuit protector.

William

Reply to
William R. Walsh

Try a vendor that supplies repair parts. These things were widely used in VCRs & TVs in the 80's. My 2006-07 MCM catalog shows them for $0.59 ea., qty 1 - 9. The catalog also lists the current rating as 0.4 amps, so you could just wire in a regular fuse (although 0.4 A isn't a standard fuse rating)

Reply to
Mike WB2MEP

Nah, one of those 100uF caps is just intermittent that's all. Seen it before. You'll just need to catch it in a shorted mode.

Mark Z.

Reply to
Mark Zacharias

I wonder if you could use a Polyswitch or similar PTC thermistor to provide the necessary protection? Their cutoff isn't as sharp as the Rohm part, but might be adequate for protection, and they're pretty easily available in small quantities (e.g. Digi-Key and Mouser).

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Reply to
Dave Platt

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