Fixing Unstable Turntable Speed

Technics SL-1300 direct-drive automatic turntable

Am I the only one who finds it odd that in 35 years,

no one ever removed that giant vinyl decal?

The thrift store can be a good place to buy turntables as well as records. You might have to be patient and keep checking, but it's not unusual to find a nice, vintage workhorse capable of outperforming many of the new turntables available today, and for a fraction of the cost.

I once found a beautifully kept Technics SL-D2 that barely needed so much as a light dusting. But most of the time there has been at least one or two things wrong with the thrift store turntables I have encountered. This Technics SL-1300, which I recently picked up, was missing the headshell/cartridge/stylus assembly, and while the sticker on the dust cover states that it has been tested and the "turntable spins," I could see by the wildly fluctuating strobe pattern, when I tried it out in the store, that the sound was going to be wobbly, to say the least. But for the low, low price of only $3.00, it didn't take long for me to decide to grab it. I reasoned that if it couldn't easily be fixed, it was still well worth buying just for the platter mat alone.

Symptoms

The video at right demonstrates the erratic strobe pattern and sound. The speed adjustment controls were extremely touchy. I only had to lightly tap them to make the platter spazz out even worse. There was no way you could stabilize the speed, and the turntable was unusable in this condition—unless you wanted to play background music in a funhouse. Watch the bottom row of dots. Those are the ones that should be appearing stationary.

Diagnosis

What can happen is, the components that allow you to control the speed get dust and crud gunking up their internal contacts, causing them to work erratically. It's the same thing that causes crackly, touchy, volume controls. Eventually, the potentiometers ("pots") and switches need to be cleaned with a good electronic parts cleaning fluid. Often, this is all that is necessary to get things working properly again. I was able to fix this problem without buying or installing anything. The only tools needed were basic Phillips-head and flat-head screwdrivers.

Solution

CRC QD Electronic Cleaner

There are several brands of cleaning fluids available that should do the trick. DeoxIT® by Caig Laboratories has a very good reputation, and is pretty much universally endorsed. I already had this can of CRC QD Electronic Cleaner hanging around, so that is what I used. Make sure whatever you use, that the label states it is safe on plastics. I should mention that a lubricant is recommended (if not essential) when/after cleaning potentiometers to keep them operating smoothly and to protect against premature wear. DeoxIT® already has a lubricant mixed with the cleaner. The CRC is a very effective cleaner, but contains no lubricant. Now that this turntable is spinning properly again, I plan to replace its audio cables. At that time, I'll probably go ahead and lubricate the pots I just cleaned.

CAUTION: Always be sure the power plug of any electrical device is disconnected from power source before working inside device. Always follow standard safety guidelines for working with electrical devices. We at Thrift Store Record Report are not responsible for any damage to persons or property that may arise as a result of unqualified service personnel attempting turntable repairs after viewing the materials posted to this site.

Disassembly

Tonearm locked and platter removed

Before turning the unit over, lock down the tonearm, remove the mat, and carefully remove the platter. Some turntables may have screws on the platter, or a retaining ring or clip of some sort around the spindle that will need to be removed first. With this Technics, and many of the other turntables I have encountered, you only need to lift the platter. It might be a little stuck at first. You can lock your thumbs in the holes and push downward with your fingers on the base if you need a little extra leverage. Try to pull up with equal pressure on each side. You have to be especially careful not to damage the magnet assembly attached to the underside of the platter on these direct-drive turntables.

Inside view of Technics SL-1300 turntable
The main speed pots and speed selector switch
are in the upper-left corner

I left the dust cover on and flipped the unit upside down on a large, folded bath towel. I know this leaves a chance of cracking the dust cover, but I've not broken one yet, and it is easier for me this way, so I continue to take my chances. If you rig something up to support it without the dustcover, just make sure it is stable enough and that nothing can touch the tonearm assembly. Next, I removed the screws from the base. The feet did not need to come off, as on some turntables. There were two screw lengths. The shorter ones went around the perimeter; the longer ones closer to the middle. I pulled all the screws out (a magnetic tip screwdriver comes in handy here) and put them aside where they wouldn't get lost. Some people like to only loosen them, so they lift out with the base, still sitting in their respective holes.

Getting Down to Business

The primary targets are the main speed/pitch adjustment pots. I cleaned only those at first, then did a quick test, and found that the speed looked greatly stabilized just from those parts getting cleaned. However, to be thorough, I went ahead and cleaned the speed selector switch and the more hidden set of speed control trimpots. I also oiled the motor shaft while I was at it.

The video above illustrates, step-by-step, all of the work that was done, and is a live-motion companion to this written article. It even has a pretty snappy soundtrack—so check it out!

The main speed control potentiometers

Spray the cleaner in any openings you find in the components. The pots should have sizable openings where the three connection tabs are attached, as well as another small one around the outside of the case. After spraying fluid inside the housing, the pot shafts need to be fully rotated back and forth many times, then repeat the spray/rotation procedure at least once or twice more.

Spraying speed selector switch

Next, I cleaned the speed selector switch by spraying into the cracks where the plastic plunger piece comes out of the housing, and in some adjacent slots, as well. The switch should then also be worked back and forth several times and sprayed again. This fluid dries very quickly and doesn't seem to harm anything it gets on, so I don't usually worry too much about over-spray, but you can always surround the parts you're spraying with a rag or paper towel to catch the excess.

To get at the second, less accessible set of speed controls, the circuit board located next to the main speed pots must be removed. It was only a matter of taking out three Phillips-head screws and then lifting the board straight up while wiggling it a little bit to free its connecting pins from the holes they mate with on the motor board.

Variable resistors 1 & 2
aka VR1 & VR2

Once the circuit board is unscrewed and flipped over, it's an easy job cleaning these parts, as they are not sealed in housings and their track and wiper contacts are more exposed. Spray, fully rotate shaft back and forth, and repeat the cycle, just like with the first pots. After everything is reassembled, these trimpots will need to be adjusted first, to give the topside speed controls the range necessary to get the platter rotating at the right speed.

Oiling motor shaft on Technics SL-1300

As long as the platter was off, I figured it was a good idea to also oil the motor shaft—especially since this is something else that can affect the speed. Technics recommends doing this after every 2,000 hours of service. Since I bought this turntable used, several decades after it was made (and while it's in pretty good shape, it doesn't exactly look like it's been babied), I think it is probably overdue by now. The owner's manual and the sticker on the platter insist you use only the specially formulated Technics oil, but I doubt it is necessary. I would certainly use it if I had some, but since I don't, I'm inclined to just make-do with an acceptable substitute when working on a broken-down, three dollar turntable. I think a good light oil, such as sewing machine oil is fine for this task. If you would like to get the official Technics oil, you can find some available for purchase at the Kab Electro Acoustics website. I used something called Lubit-8. I like the precision needlepoint applicator and the fact that it is supposed to be compatible with all oils and greases, so it should mix well with any other oil that has been applied in the past. No matter what kind you use, you are only supposed to apply two to three drops.

These are basically "set and forget" trimpots

I didn't note the positions of VR1 & 2 before commencing to vigorously rotate them, so I reset them to the midway/twelve o'clock position. After trying out the turntable, I found they needed to be moved to the one o'clock position. VR1 and VR2 must be set correctly before the topside controls will have the range needed to get the platter spinning at the right speed.

Results

The video below shows how the turntable is running very smoothly now.

A nice Technics turntable database can be found at Vintage Technics 

 

A great library of free turntable user manuals, service manuals, schematics, brochures, and technical documents is located at Vinylengine