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-   -   Technics SL-1200 Speed Issue (http://www.diyaudio.com/forums/analogue-source/169273-technics-sl-1200-speed-issue.html)

Loren42 25th June 2010 02:21 AM

Technics SL-1200 Speed Issue
 
My SL-1200 turntable speed is going crazy.

I tried cleaning the speed slide switch, but to no avail. Moving the speed selector or changing speeds to 45 RPM does not help, so I am thinking it is the PLL circuit that has a bad component.

Does anyone know where I might find a service manual?

I am hoping that the electronic parts are still available, but many of these types of parts go obsolete, too.

ashok 25th June 2010 03:12 AM

Try Vinyl Engine | The Home of the Turntable
You have to register to download manuals that you will find under the "library" menu. You can browse around without registering.
Several versions of the SL1200 are mentioned though the service manual for all are not listed. I would guess they all have the same drive system and so any manual for a SL1200 might be good enough.

Cheers.

968driver 25th June 2010 06:10 PM

I would replace the pitch control potentiometer. In almost all cases, this is the cause of the speed problem!

bob91343 25th June 2010 07:05 PM

I don't think it's the pitch control pot because that gets switched out when you don't want pitch control. There are two pots, one external and the other internal; only one at a time is used.

968driver 25th June 2010 09:14 PM

Try replacing the outside slide potmeter.
In 99% it is the cause of the speed problems!

Loren42 29th June 2010 02:16 AM

Quote:

Originally Posted by 968driver (Post 2227132)
Try replacing the outside slide potmeter.
In 99% it is the cause of the speed problems!

When you say outside pot, is that the fader or a trimpot inside on a board somewhere?

By the way, is that 968 a P-car?

968driver 29th June 2010 06:30 AM

Hi,
I think the fader is the problem. You could try to open it and clean the carbon tracks and slider contacts very carefully, to see if this has any effect.
Just spraying some contact cleaner in the fader is mostly unsuccesfull.
The 968 is my P cabriolet of 1993.

Loren42 29th June 2010 06:45 PM

Quote:

Originally Posted by 968driver (Post 2230111)
Hi,
I think the fader is the problem. You could try to open it and clean the carbon tracks and slider contacts very carefully, to see if this has any effect.
Just spraying some contact cleaner in the fader is mostly unsuccesfull.
The 968 is my P cabriolet of 1993.

I sprayed contact cleaner from the top with no change.

I am going to open it up and try substituting a pair of fixed resistors to see if the jitter stops. If that works, then I will order another slide pot.

I'll let you know what I find.

The 968 is a beautiful looking car and the Cab more so.

I have owned just about every 944 derivative (except the 944S2), but never got a 968. Enjoy the drive!

968driver 29th June 2010 07:54 PM

Do you have a service manual for the 1200? I think I have one in pdf format and could email it to you if needed.
A lot of 1200's are used in clubs and disco's, and very often some beverage is spilled on these turntables and into the speed control fader, with erratic speed as a result.
I have replaced dozens of those faders (I do this kind of stuff for a living).

There is also a medium power transistor bolted on the inner part of the chassis, on a tiny connecting circuit board. Check the solder pads of this transistor, they may become loose in a rare case.
Also check the main PCB for bad solder pads.
Check if the chassis is dry. Some DJ's play the records wet (spray water on the disc) to avoid static electricity. This ruins the speed pitch fader and eventually also the power transformer of the turntable.

Finally, in a rare case (these turntables are very well build and virtually indestructable), the fault can be in the electronics.
First check power supply voltages.
If you have an oscilloscope, check the quartz oscillator and drive circuits.
You will need the schematic if the fault is in the electronics!


PS:
I very much enjoy the 968, especially on sunny days and open driving. I think the 968 Cab is a design classic, as yet not fully appreciated in general!

Loren42 30th June 2010 12:35 AM

Quote:

Originally Posted by 968driver (Post 2230666)
Do you have a service manual for the 1200? I think I have one in pdf format and could email it to you if needed.
A lot of 1200's are used in clubs and disco's, and very often some beverage is spilled on these turntables and into the speed control fader, with erratic speed as a result.
I have replaced dozens of those faders (I do this kind of stuff for a living).

There is also a medium power transistor bolted on the inner part of the chassis, on a tiny connecting circuit board. Check the solder pads of this transistor, they may become loose in a rare case.
Also check the main PCB for bad solder pads.
Check if the chassis is dry. Some DJ's play the records wet (spray water on the disc) to avoid static electricity. This ruins the speed pitch fader and eventually also the power transformer of the turntable.

Finally, in a rare case (these turntables are very well build and virtually indestructable), the fault can be in the electronics.
First check power supply voltages.
If you have an oscilloscope, check the quartz oscillator and drive circuits.
You will need the schematic if the fault is in the electronics!


PS:
I very much enjoy the 968, especially on sunny days and open driving. I think the 968 Cab is a design classic, as yet not fully appreciated in general!

This must be an early table. I can't find a schem for it. The ones I found have a reset switch on the schem that I don't have on my turntable.

I just want to solder a trimpot in place of the slider. If the slider is bad a new trim pot will prove that.


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