Technics SL-5 behaviour problem!

musicmantech · 8th June 2009, 09:12 PM

Hi All!
Have recently acquired a like new looking SL-5 that has a mysterious problem.
When you play a record everything appears to be fine. Everything functions as it should, but........ Once in a while the arm transport
mechanism will go wild and will move the arm towards the center
slowly, but too fast. It will then scratch over the record surface towards the center.
When you look at it whilst it is happening the arm is at an angle
as it is dragged along to the center of the disc.
Have the manual but this is not covered as a symptom.
Any idea's about this and possible solution of this behaviour wouldbe greatly appreciated! Thanks,
Rob.

Triophile · 27th June 2009, 09:02 PM

Hi Rob.

You might well find that the problem here is an intermittent contact in one of the various switches on these decks. That said, if there's something wrong with the phototransistor which I seem to remember measures arm deflection and moves the arm carriage to compensate, that might cause the same prob.

I put up the manual for the SL-7 (at Geocities), and some of the circuitry might be sufficiently similar that you could use it to fault-find on the SL-5. Whatever the cause, giving all the switches a spray with contact cleaner will almost certainly be a good idea.

Cheers, Jon.

musicmantech · 23rd July 2009, 04:13 PM

Hi Jon!
Thanks for your advice!
However the fault was somewhere else.
There are detailed instructions in the service manual on how to
fine-tune and regulate the voltage on the dedicated test points
to have exactly 18 Volts when the arm is in the middle position.
Because of age related component value drift, this centre position arm steering voltage was hugely off. Lower than 15 V. This means that the steering mechanism "thinks" that the pivot point should travel to the centre .
In this case I re-regulated the tracking voltage with the standard arm positions and fine tuned it with the exact positioning of the
related circuit board, as described in the manual and presto, all is well again.
Switch contact oxidation is still playing a role in the muting relais which is not working properly all of the time. That one has to be cleaned yet!
Thanks again,
Rob.

8th June 2009, 09:12 PM	#1
musicmantech diyAudio Member Join Date: Jun 2009	Technics SL-5 behaviour problem! Hi All! Have recently acquired a like new looking SL-5 that has a mysterious problem. When you play a record everything appears to be fine. Everything functions as it should, but........ Once in a while the arm transport mechanism will go wild and will move the arm towards the center slowly, but too fast. It will then scratch over the record surface towards the center. When you look at it whilst it is happening the arm is at an angle as it is dragged along to the center of the disc. Have the manual but this is not covered as a symptom. Any idea's about this and possible solution of this behaviour wouldbe greatly appreciated! Thanks, Rob.

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27th June 2009, 09:02 PM	#2
Triophile diyAudio Member Join Date: Sep 2004 Location: London	Hi Rob. You might well find that the problem here is an intermittent contact in one of the various switches on these decks. That said, if there's something wrong with the phototransistor which I seem to remember measures arm deflection and moves the arm carriage to compensate, that might cause the same prob. I put up the manual for the SL-7 (at Geocities), and some of the circuitry might be sufficiently similar that you could use it to fault-find on the SL-5. Whatever the cause, giving all the switches a spray with contact cleaner will almost certainly be a good idea. Cheers, Jon.

23rd July 2009, 04:13 PM	#3
musicmantech diyAudio Member Join Date: Jun 2009	Hi Jon! Thanks for your advice! However the fault was somewhere else. There are detailed instructions in the service manual on how to fine-tune and regulate the voltage on the dedicated test points to have exactly 18 Volts when the arm is in the middle position. Because of age related component value drift, this centre position arm steering voltage was hugely off. Lower than 15 V. This means that the steering mechanism "thinks" that the pivot point should travel to the centre . In this case I re-regulated the tracking voltage with the standard arm positions and fine tuned it with the exact positioning of the related circuit board, as described in the manual and presto, all is well again. Switch contact oxidation is still playing a role in the muting relais which is not working properly all of the time. That one has to be cleaned yet! Thanks again, Rob.

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