Technics SL-1200 Speed Issue

[Loren42]

Originally Posted by 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!

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]

Originally Posted by 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!

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.