Technics SL-1200 Speed Issue

[Loren42]

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]

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]

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

 

[bob91343]

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]

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

 

[Loren42]

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]

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]

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]

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]

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.

 

[Loren42]

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!

I think I figured it out!

The reset board is an option, so the schematic is okay. I just shorted the reset switch (center of the pot switch) so the turntable circuit thinks that the speed should be locked to the 0 pitch and it worked.

Now I need to see if it stays working or if there really is another problem lurking in the control board.

Thanks!

 

[Loren42]

I don't know how well the strobe dots are supposed to stay fixed, but there is a tiny amount of wobble from time to time. It is very slight, but visually detectable.

 

[Loren42]

After spinning a few LPs it appears that the turn table is working. Thanks, all, for the help!

 

[JAaron]

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!

Can you send me the service manual for the 1200?

Thanks,
Aaron
jaaron5@hotmail.com

 

[mixbob]

I would check the power supply first. The regulator and it's solder connections could be flaky. If voltages are stable next check the quartz crystal oscillator and verify motor connections. It is unusual for crystals to intermit or change value; so see if you can check all other components in the speed control loop.
The external speed control fader should be bypassed when pitch control is off so should have no effect. The internal trim pot is used to set the reference speed and can visually be verified by the strobe. If speed is still changing, suspect an open in the motor speed control loop.
Please post your findings. Generic parts can hopefully be found to replace what has failed. Packaging may be different and may require adaptation to fit.