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freax 1st January 2013 10:57 AM

Technics SL-1300 MkI (NOT MkII) oscillating speed problem.

I've got a serious issue with this TT.

It was working perfectly for the last few months. (This turntable has had this same problem before, which I thought I fixed for good with resoldering the motor terminals)

I then decided tonight that I would do a recap, not thinking I replaced all of the electrolytic capacitors at the same time with equivalents that I tested with a multimeter to be within tolerance, I marked down on the PCB with a thin black marker the polarity and values of the original capacitor that was in there.

Thats when problems started.

There was a huge oscillation issue, it would start out 'weak', going faster, then slower, a small amount, and then it would quickly change pace and speed up again, almost as if there is a feedback loop going on here?

Thats what happened when the new capacitors were in place.

I then figured, ok, it was the capacitors, I then replaced all of the new capacitors with the original ones, one by one I went back and replaced each capacitor, putting the original back in where it was before.

That gradually made the problem go away, one by one as each capacitor was put back into place it started to fix itself.

I then figured, okay this might be dry joint related and I've resoldered each point.

When I had finally gotten to the very last capacitor, I figured, okay, surely the problem is fixed by now, nope, it just took a longer time for the oscillating to begin again.

So then I took the motor assembly apart and resoldered every single connection on there.

So I just finished putting all of the original capacitors back in, and I set it up and listened to it for FIVE MINUTES without the problem starting again and then it finally started doing the problem again!??

So now I am back where I started.

There is very little information about how to properly recap this TT on the internet, the service manual is completely useless aside from check the Zener diodes....

I'm wondering what VR3 and VR4 do on the schematic? I was kind of hoping to do the recap again with new capacitors and fiiddle with these Variable resistors to see if I couldn't remove the oscillation?

If anyone helps me out I promise I will seriously consider getting a belt driven turntable...

freax 1st January 2013 12:55 PM

Might've narrowed it down/fixed it.

The speed selector switch, I twiddled that for a good minute and its been working perfectly now for the last 6 minutes and counting...

Forgot to clean that part!

I also prior to this desoldered/sucked all of the solder off of the PCB and went back and redone the entire thing again with fresh solder, this is the second time that I've done this.

~~~~ EDIT:
It just surged then, after playing for a good 15 minutes....

I'll have to go ahead with the recap anyway and see if I can't nail down the speed again.

freax 1st January 2013 02:45 PM

recapped it with new capacitors, managed to get it within tolerable speed variances with the new capacitors but she is still hunting around quite a lot for the center speed.

What the hell happened?

I've spent 3 hours working on this thing, about ready to pack it in.

Going to solder the motor board to the control board directly with hookup wire... just incase.

freax 1st January 2013 04:44 PM

Just finished wiring some wire directly from the motor to the mainboard.

Im currently listening to a record to see if this fix worked.

The theory is that the surging speed problem is caused by a loose connection on the arguably 30 year old pin and insert connector which goes to the motor, and the problem being intermittent is causing the sensor underneath the motor which senses the magnets going past it, creating a pulse signal, to lose connection to the mainboard and hence making the voltage regulator speed up the motor or surge until it makes contact again when it slows down and settles down. = oscillation.

freax 1st January 2013 05:08 PM

The piece of **** is still doing it after 12 ******* hours of working on it.

It is my only turntable too, and I just started getting into records again, ****!

I'm going to bed.

freax 2nd January 2013 01:27 PM

Given up on it, gone to a belt driven turntable that was given to me.

**** this overcomplicated piece of japanese horseshit.

hymenoptera 5th January 2013 05:48 AM

I frequently borrowed a Technics B200 for 33rpm to CD digital remastering when I was first getting into recording, and always had to wedge a guitar pick into the speed control to keep speed constant. Might not be a bad idea to replace the speed pot entirely with equivalent.

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