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Technics SL-B2 speed/pitch problem?

F

fcm44

Active Member
Hello,

I bought a Technics SL-B2 turntable yesterday. I had an SL-B20 before and it got the job done, so I figured this other one would be alright too.

But it has a strange speed problem. The belt is in good shape, it does fut there very well and it doesn't slide. But the potentiometer works very strangely. It isn't a going down or up in a straight line like it should, and when I finally get to the right speed (usually I have to crank the potentiometer all the way up), a small knock on the TT's body will make it go faster or much slower for second. I don't always have to even touch the TT in order to make it slower, it will become slower on its own. I just figured I could provoke that by touching the TT near the speed selector/potentiometer module.

What should I do? Is it good for the scrapyard or can it be easily fixed? I have never successfully repaired anything electronic and I wouldn't go further than opening it up (which I did without figuring what the problem was).

Please help ! Even if it's just to tell me it has to be scrapped.

 
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Try cleaning the pitch control pots with a good contact cleaner. Also, make sure the electrolytic capacitors are good, and the trim pots for speed adjustment have clean contacts. If the above measures don't fix it, try pots and trim pots first, then caps, then your motor is likely having a problem with a bad servo IC (Neither part available any longer).
 
Hi,

So I opened my turntable and sprayed the sort of cylinder/circular thing where the speed selector "wheel" is attached. That solved 90% of the pitch problems, but it still slows down from time to time. I know absolutely nothing about electronics, and I have problems differentiating "inner" and "outer" potentiometers, as I only recognize one thing to be a potentiometer, which is what I sprayed deoxit on.

I have watched a few videos over the internet but none of those had the exact same model and parts placement.
 
I found the owner's manual and took a screenshot. I sprayed the cylinder thing that looked like a potentiometer right where the red circle is right there. Is it where I should have sprayed? It did fix 90% of the issues, it made the TT worth some use, but if I knock on the TT, you can still see a drop in pitch/speed.
 

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The inner pots are there too in your image, highlighted below:

IMG_20201019_074708.jpg

As it turns out I have a similar Technics on my bench now. It's an SL-B10 and here are it's pots in the lower left, marked 33 and 45. They are on the other side of the circuit board but the holes through the board and bottom panel allow access.

IMG_20201019_082931.jpg


The technique with cleaning these is to center the outside trim pot in its range first and then to spray one of the inner ones at a time and turn it through the full range multiple times, then do the other one. Take note of where the control is before you start and likely you will end up at or very near the same position. Do not move the outer control yet; use the inner ones to get the strobe stationary at both speeds. Doing it this way you still will have full left/right adjustment when using the turntable. You also should be able to change from 33 to 45 without having to readjust the control.
 
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Thanks a lot! I have found them all, sprayed them all, turned the pitch knob back and forth 40 times, repeat, and my turntable now works like a dream. You're welcome !!
 
I've got one of these that I bought new. But now it has the same issues.
Looks like this is the direction I need!

I'll give it a little attention as shown here. We'll see what happens.
Thanks Guys!
 
Got it apart, sprayed the pitch control pot, worked it back and forth multiple times. But it still has the same problem. I can't seem to get the proper speed on 33. The closest I can get is with the speed as fast as it will go, but the recording sounds like it slows down?
Don't understand what I'm doing yet I guess. I'm at the max of speed control, but the record is too slow!

Haven't touch the variable trim caps yet. When you adjust these caps, what do you look for? ie: How do you measure what your adjustment is?
 
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You don't have to measure anything, just use the technique I described above. The strobe is your gauge. Just make sure the pitch wheel is at least roughly centered when turning the internals.
 
Thanks Monty,
Here's where I am so far. There is an access from the top, but I don't have a screwdriver that will reach the Var. pot. So I have to remove the table and turn it over for every adjustment!

I've made 3 or 4 adjustments on the 33 speed but not much change. Not sure I always had the speed control centered when I did it however. Would that be critical when I'm making the adjustment?
 
Soup cans. Or something else you can elevate the edges of the turntable on with the bottom removed while turning the VRs.

The top control doesn't have to be in the exact center but in order to have a reasonable +/- range it should be very close to it.
 
Man! That was easy. I've been fooling with this thing all day, and after I got it propped up, it took about 30 seconds!
Montycat, If you were here right now I'd give you a big kiss! :banana::)
 
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