Sl-7 Disassembly Problem

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Dave in Green
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SL-7 Disassembly Problem

Post by Dave in Green » 01 Dec 2009 01:18

I recently resurrected my Technics SL-7 from storage, and it appeared to be working just fine on the first track of the first album I tried. But after about a minute it stuck on one groove and would move no further. I realized that the tone arm drive was apparently not functioning. Sure enough, after using the cue button to raise the tone arm, pressing and holding the start button resulted in no movement of the tone arm.

Thankfully I discovered this website, and read about the tonearm belt and motor seizure being the most likely problems. So I registered, downloaded the SL-7 service manual, and carefully read and followed all the instructions for disassembly. But when I tried the first step of removing the cartridge, I could find no way to get the tonearm to move from its 30cm resting position to the 25cm position.

I was able to safely get the cartridge out in the 30cm position, and thought I was home free. Then I discovered that one of the 7 screws that must be removed to take off the dust cover is right under the tonearm in its 30cm resting position.

Finally, the big question: How on earth does one get to that 7th screw under the tone arm in the 30cm resting position in order to remove the dust cover if the tonearm will not move out of the 30cm resting position?

I am really stumped on this one, and would be grateful for advice from anyone who has a working solution.

flavio81

Post by flavio81 » 01 Dec 2009 01:27

So I registered, downloaded the SL-7 service manual, and carefully read and followed all the instructions for disassembly. But when I tried the first step of removing the cartridge, I could find no way to get the tonearm to move from its 30cm resting position to the 25cm position.
The answer is in the user manual, on the section for cartridge/stylus replacement.

Anyway, just set the record size to 25cm, press play even with no record on, and the arm will go to the 25cm pos. Then just power down the turntable.

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Post by Dave in Green » 01 Dec 2009 02:55

flavio81 wrote:
So I registered, downloaded the SL-7 service manual, and carefully read and followed all the instructions for disassembly. But when I tried the first step of removing the cartridge, I could find no way to get the tonearm to move from its 30cm resting position to the 25cm position.
The answer is in the user manual, on the section for cartridge/stylus replacement.

Anyway, just set the record size to 25cm, press play even with no record on, and the arm will go to the 25cm pos. Then just power down the turntable.
Thanks for the quick reply. The service manual says the same thing as the owner's manual, and I followed the instructions to the letter. Pressing play even with no record on no longer causes the arm to go the 25cm position. Nothing I've tried will make the arm go to the 25cm position or even move a fraction of an inch. It appears to be frozen in the 30cm position.

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Post by Shoji » 01 Dec 2009 08:20

Hello. If require to move tonearm by manual method is necessary to remove black plastic cover inside top cover. When remove is then possible to turn cord drive assembly by hand turn of motor drive pulley.

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Post by Dave in Green » 01 Dec 2009 16:06

Thank you. But I cannot remove the black plastic cover inside the top cover because one of the screws that holds the cover in place is hidden behind the tonearm.

I cannot find a way to remove the cover without first moving the tonearm, and I cannot find a way to move the tonearm without first removing the cover.

The manual says: CAUTION: Never attempt to move the tonearm by hand. This may seriously damage the delicate tonearm drive mechanism.

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Post by Shoji » 01 Dec 2009 16:24

Hello. In such case may be possible for release all screws as possible for black cover and try make gentle lift of low left corner to make the access for pulley on motor shaft end ? Manual caution that say about not move tonearm by the hand is correct. This caution is for any one try to make tonearm move when grip tonearm body by the hand. Is OK if access to motor shaft pulley and able to make gentle turn of pulley to make worm drive plus the drive cord assembly turn as if motor working. When make motor shaft pulley turn by hand take many turns to make only small movement of tonearm assembly so take some time for this method :D

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Post by fscl » 01 Dec 2009 18:28

DiGreen writes:
Finally, the big question: How on earth does one get to that 7th screw under the tone arm in the 30cm resting position in order to remove the dust cover if the tonearm will not move out of the 30cm resting position?

I am really stumped on this one, and would be grateful for advice from anyone who has a working solution.
EXACTLY ](*,) ](*,)

What I found when my SL-7 acted up.

My solution.... was to CAREFULLY & GINGERLY use a thin shaft Phillips head screwdriver with the tonearm displaced as far left as it would go and the screwdriver blade well seated and at an angle to the right. Luckily, it's not tightened too hard and was able to break loose and back the screw out and get into the internals and manually turn the worm gear to about 25cm. Needless to say, you will have to release / cannot use the tonearm lock. I just checked with my own unit, if the tonearm stops in the correct location, unlocking the tonearm and displacing it left will uncover this last screw. The problem with mine when she started misbehavin' was that the tonearm continued to be driven into the side cover and thus burning out the original belt leaving this screw still partially covered by the tonearm even when displaced fully left so I had to use the screwdriver at an angle. When in there for servicing, check, clean and adjust all limit switches especially the tonearm out switch.

When this happened again, I now simply do not reassemble my SL-7 with this screw in place.

Good luck.

Fred and you'll love the SL-7 and the Technics linears when you get this sorted :)

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Post by Dave in Green » 01 Dec 2009 18:43

That worked! Many thanks to you, Shoji. I was able to get my little finger in under the edge of the cover and turn the pulley until the arm moved away from the screw. Then I could remove the screw and the cover.

Now I have to figure out what is wrong. Everything turns smoothly, including the gears. The grease is still soft and not binding the gears. The drive belt for the tonearm motor even looks OK. But for some reason the tonearm motor will not run. I read on another forum that one person who repairs turntables said he had never seen a tonearm motor fail on an SL-7. It was always something else that caused the problem and not the motor itself.

I am fairly handy mechanically, but I am not too experienced with electronics. So unless someone can tell me what to look for in simple terms, I still might have to find a repair service to look at it.

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Post by Shoji » 01 Dec 2009 18:57

Hello. Is then good news for success in the cover removing :D Is possible make check of tonearm motor. Look to RED and the BLUE wire from motor and dis connect from circuit. If use small 9v battery to motor wire RED plus the BLUE is possible to see motor operation OK. Is possible to make connection both way for polarity to make the check for both direction of motor. Most time with this type model turntable is wire connection problem so make the check. When check motor function OK then may be require make check of motor drive circuit.

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Post by Snead » 01 Dec 2009 20:19

Dave, when I first got my SL7 the motor was frozen i.e. it wouldn't turn.

All I did to free it was to turn it by hand using pliers to break it loose. Then a new belt, and it's been my daily driver ever since.

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Post by Dave in Green » 02 Dec 2009 03:29

fscl, thanks for your suggestion. I tried Shoji's suggestion before I saw yours, and Shoji's suggestion worked. It sounds as if your solution with the small screwdriver would also have worked.

Snead, the first thing I tried when I finally got the cover off was to turn the motor shaft as you suggested. It turned easily, so it was not frozen.

Shoji, I followed your suggestions exactly. I connected the red and blue wires to a 9v battery both ways with polarity, and the motor spun in both directions. But the belt was bad and would not turn the gears. I was lucky to have a small rubber o-ring that was almost exactly the same size as the tonearm motor belt. When I put it on and ran the motor with the 9v battery, it turned the gears.

So I reassembled everything, and when I held down the start and stop buttons, the tonearm moved back and forth in both directions. Success!

But when I put a record on to play, the tonearm sometimes moved forward and sometimes stopped and wouldn't move forward. So I played around with holding down the start and stop buttons. I found that if I pushed down hard, the arm would move quickly back and forth every time. But when I pushed down gently, sometimes the arm would move and sometimes not.

I think what may be happening is that the whole gear system is a little "sticky" so that the motor can drive them at high speed but not at low speed. I am going to take everything apart again, clean off all the old grease and lubricate every part of the gear system that moves the tonearm back and forth. I have a tube of "Super Lube" synthetic grease that I think will work really well to make everything run more smoothly, even at slow motor speeds. I'll report back here after I do that.

What a great forum this is! You are all so helpful. I plan to stay active on this forum and hope to be able to Help others the way you have helped me with this problem.

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Post by fscl » 02 Dec 2009 18:41

DiGreen writes:
But when I put a record on to play, the tonearm sometimes moved forward and sometimes stopped and wouldn't move forward. So I played around with holding down the start and stop buttons. I found that if I pushed down hard, the arm would move quickly back and forth every time. But when I pushed down gently, sometimes the arm would move and sometimes not.

I think what may be happening is that the whole gear system is a little "sticky" so that the motor can drive them at high speed but not at low speed. I am going to take everything apart again, clean off all the old grease and lubricate every part of the gear system that moves the tonearm back and forth. I have a tube of "Super Lube" synthetic grease that I think will work really well to make everything run more smoothly, even at slow motor speeds. I'll report back here after I do that.
She's gettin' there...... :)

Sleeping Beauty's gotta be exercised, microswitches, contacts and sensors all have to reawaken by contact cleaner and use (wearing away oxides)... etc... and then when it's all clean, electrical measurements and adjustments back to spec.

The <<>> Technics linear buttons are 2 step buttons, 1/2 press / depression advances / reverses at a slow rate, full press = fast rate. So perhaps the 1/2 press electrodes are dirty resulting in intermittent advance / reverse. I don't think they can be easily cleaned but seem to respond to repeated usage.

The intermittent movement while the tonearm is on an LP sounds like a dirty offset sensor and / or some control voltages out of spec.

I've pretty much tried to remove all of the old grease from the tonearm drive mechanism. There's more than enough on all the linear's I've come across and find the remaining light / thin coat of remaining grease after cleaning is enough supplemented with a modern lightweight Teflon based
lube on the tonearm guide rod.

flavio81 has an excellent suggestion, lifted from another SL-7 topic, and that is to use / hold the "Open" button when closing the dust cover and not letting it snap shut. The latches that hold the dust cover down are plastic and can / may break. This is why my SL-7 is in semi retirement, one of the cover latches broke :( and I need a heavy book / weight to hold down the cover when playing LPs.

Good luck.

Fred and thinking hard on a latch solution as the dust cover is no longer available as a replacement part..... :?

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Post by Dave in Green » 02 Dec 2009 23:22

fscl, I just finished cleaning all of the old grease out and replacing it with a very light coat of "Super Lube" synthetic grease. I also used a light coat of teflon oil on the tonearm guide rod. The tonearm mechanical mechanism is working really smoothly and easily now.

But the problem remains that while a full press on the 2 step buttons always gives full speed advance or reverse, a 1/2 press only intermittently results in slow speed advance or reverse. On the times when I do a 1/2 press but the motor doesn't run and advance the tonearm, I can even hear a small click from the rear of the SL-7 as if a swtich is responding but perhaps not making complete contact. It does seem to be working more often the more I use it, so maybe that will come back with use. I may also trace down the switch and try cleaning it.

The worse problem is that the tonearm will usually not advance at all when I play a record. Since it does advance occasionally, it does have all the symptoms of a dirty sensor or something out of spec. I just looked through the service manual and couldn't find a reference to the location of the offset sensor. If you can point me to the offset sensor, I'll have a go at cleaning it. But it may also be that the sensor is sending a signal to the same switch that only intermittently works for slow speed advance.

The advice to hold down the open button while closing the cover is excellent. I just looked at the latches that hold down the cover and realized how weak and flimsy they are compared to the rest of the SL-7.

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Post by Dave in Green » 03 Dec 2009 17:31

It looks as if Sleeping Beauty does respond well to exercise. The more I push buttons and keep it running, the more it improves.

It's now reached the point where a 1/2 press results in slow speed advance or reverse more than 80% of the time.

Even better, when I start playing a record from the beginning, the tonearm no longer sits frozen but will now advance as many as 7 or 8 times in small steps before it stops advancing.

I'm just going to continue to listen to my old vinyl 1 track at a time and see if the SL-7 reaches the point that it can play a full album from beginning to end.

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Post by fscl » 03 Dec 2009 17:53

DiGreen experiences:
I can even hear a small click from the rear of the SL-7 as if a swtich is responding but perhaps not making complete contact. It does seem to be working more often the more I use it, so maybe that will come back with use. I may also trace down the switch and try cleaning it.

The worse problem is that the tonearm will usually not advance at all when I play a record. Since it does advance occasionally, it does have all the symptoms of a dirty sensor or something out of spec. I just looked through the service manual and couldn't find a reference to the location of the offset sensor.
First try displacing the tonearm through it's full range of movement a few times with the power and the tonearm lock / safety off. Then exercise <<>>, in-out, in-out... etc....as it seems to be getting better. I also try to clean the related plug in connectors on the pcbs

I was looking at page 12 of the Service Manual "Adjustment" section and in particular "Offset adjustment of tonearm and servo gain" section and read through and follow the instructions on page 13 and 14, Steps 2, 3 and 4. Hopefully this will cure the skip problem while the tonearm tracks an LP.

Offset angle detect sensor is an LED / Sensor combination, @ PC 401 on the IC 301 block diagram. I believe this optical sensor is located in the tonearm support well opposite to where the hex wrench is inserted to adjust the centering voltage. You may want to gingerly "blast" some air in this well where the "T" goes into the tonearm support and dislodge any dust / dirt prior to centering adjustment voltage. (ie a turkey baster or something that can push some air quickly and semi forcefully, I think new canned air may be a little too strong unless you've got a "low" canned air bottle).

After displacing and moving the tonearm and application of air, try playing a record again. You may have cleaned the sensor to bring the fine tonearm movement back. If not continue with voltage measurements and adjustments according to steps 3 and 4. A 1 mm test LP will be difficult to find, however, I believe you can use a standard LP for adjustment of the voltages. You really want the voltages correct while moving across one of the vinyls in your collection.

Good luck. Hopefully this will get you spinnin', trackin' and postin' in Currently Playing....

Fred and refer to page 30 for the tonearm connections to clean leading into the pcb, 111 for audio signal and 110 for tonearm drive.....

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