Sl-1710 Mkii Repair Of Cueing And Auto Return

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SL-1710 MkII Repair of Cueing and Auto Return

Post by Head Tomcat » 19 Jul 2009 15:53

All,

My first post here and looking for help on repairing the cueing and auto return function of my SL 1710 MkII turntable.

Some history...I am the ORIGINAL owner of this table and bought it in the Schweinfurt, Germany, Audio Club in November, 1980. Has provided incredible service all these years and I am now interested in burning my large collection of LP records onto CD so I can play them in the car.

Years ago the cueing function and auto return failed...and cruising this very good site indicates the belt has probably worn out. I have also read it can be replaced in about 10 minutes with a #39 o-ring, etc. The problem is I have found no detailed instructions on how to actually access the old belt and then install the new one.

How do you get to the old belt? Where is it located? I have already found the user/service manaul .PDF's for this machine...but am still looking for guidance on where to start the repair.

Many thanks for your help...just reading the many posts on this site has brought back so many great memories of the waning days of vinyl!

The Tom

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Post by analogaudio » 19 Jul 2009 17:41

This applies to SL-1600mk2 and 1700mk2.

Unplug power, remove the platter, lift gently but firmly with your fingers in the holes. Use a small Philips screwdriver to loosen five black screws that secure the rim of of the big black trim piece to the chassis. This uncovers the guts.

The motor and drive belt is located at about 2 o'clock in the chassis near the arm there is a tiny brass pulley on the motor and a much bigger white plastic pulley on the drive mechanism. Look for the pieces of the old belt and take them out with tweezers. Fit the new belt. Turn the pulley with your fingers to make sure the belt is properly seated.

Put the trim cover back.

Check around the central spindle that nothing fell in the magnet and coil area. Put the platter back.


Good Luck

Ted

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Thanks! Replaced the belt...and still no movement.

Post by Head Tomcat » 19 Jul 2009 20:02

Ted,

Many thanks for your rapid reply!

I did just what you said and found (as expected) the factory OEM belt which is now 29 years old had cracked and broken into three pieces. They were still in big sections so I easily got them all out and then replaced it with a suitable o-ring. The magnets around the platter and coil were all clean and appeared as new.

However, when it was all put back together and I was giving it the final test....the arm does not move. When I push the cueing buttom to raise the arm nothing happens. When I manually move the arm it automatically turns on the spindle and things run well. However, when I get to the end of the record the arm will still not automatically return to the storage position.

I have checked and the button at the right rear of the base is pushed in, which is the auto return "On" position. The cueing arm (sorry for bad nomenclature...it is the curved platform which raises the arm) can easily be lifted up/down with gentle assistance from my finger.

So, it seems that something else may be wrong, too...in addition to the broken belt. The cueing switch? All other switches seem to work, though. The motor which raising the cueing arm?

Thanks for any advice!

The Tom

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Post by analogaudio » 19 Jul 2009 22:14

I'm not sure what is wrong, here's what I'd do if it was mine.

This involves operating the unit with power on and the cover open so you can get at the arm motor and the white pulley wheel. Take care, there is AC power that could shock you but the exposed live terminals are on the opposite side of the TT at least in units I have seen.

Can you see the brass pulley? Is the belt still in place? If not put it back in place and try again.

With power on does the arm motor run when you operate the CUE button?

If not, with power off what happens when you turn the brass pulley with your fingers? Does the arm raise? Turning one way raises the arm, turning the other lowers it. The mechanism is driven by the motor first in forward to raise then in reverse direction to lower.

It may be that the system has got hung up in an intermediate state, half way through a cycle. If the arm mechanism can be driven by turning the pulley by hand keep turning it until the arm reaches full height then put the power on and see if has recovered by using the CUE button.

It is OK to put power on and off with the platter removed but don't remove or replace the platter with power on, do that only with power off. The green electromagnets can attract magnetic debris like small screws and metallic particles.

Try that and see what happens.

Keep your hands well away from the exposed AC terminals, not just your right hand but also the one you lean on!!!!

Ted

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Still no joy...

Post by Head Tomcat » 19 Jul 2009 23:24

Ted,

I have followed your very good instructions and so far there is still no movement of the arm.

The o-ring is properly installed on the small brass pulley and also on the large white plastic one, too. I can use my fingers to slowly spin them and they move without any restrictions or unusual feelings of roughness.

My Fluke digital multimeter shows that 124.1v AC are coming into the table and no broken wires or anything looking wrong (ie, spilled fluids, loose components, etc.). When I check the small arm motor that has the brass pulley...I show that .704 v DC are going into it. So...some degree of power is going into that motor.

What is interesting is that when I spin the white plastic pulley I see absolutely no movement of the mechanism which is supposed to raise and lower the arm. I would think that if this plastic pulley was spun...and assuming it was correctly attached to the lifting mechanism...then that arm should be moving a bit.

So...at this point the small motor does not spin when the cue buttom is pushed...however, power is going to that motor...and the lifting mechanism still does not move in the slighest when I manually spin the white plastic pulley.

Any thoughts?...and thanks so much for your help so far!

The Tom

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Post by analogaudio » 20 Jul 2009 01:26

If I understand correctly nothing so far has made the motor turn. Seems to be a double-fault, the bad belt plus something else we don't yet know.

All removable connectors (black plastic) should be checked there may be one loose, partly disconnected, unplug them all one at a time (power off) and replace it one by one, there may be a bad contact that will get wiped clean by the separation and remating of the two connector parts.

There may be some fuses on the AC power circuit board, these are shown in the service manual. Power off they should read zero Ohms resistance.

The next step is to open it up and take a closer look at the mechanism. It is a combination of microswitches, optocouplers and a circuit board. DC power comes from the central platter printed circuit board. There is a cam that lifts the arm, it is driven by the motor via the pulley and a worm gear reduction drive.

There is a white plastic gear in the motor drive train it is about 3/4inch diameter engages with a bigger double white gear wheel. The smaller gear wheel provides motion to swing the arm, it can crack and split but that shouldn't stop the arm raising mechanism from working. My hunch is these is something simple gone wrong with the mechanism but it difficult to know what it is exactly. Fuses and connections defintely should be checked, they are easy.

As it happens I have a 1700Mk2 on my bench right now in pieces, I am restoring it so I have the arm completely removed from the chassis so it is easy to look and check stuff.

If I have more ideas I'll let you know.

Ted

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Thanks!

Post by Head Tomcat » 20 Jul 2009 01:43

Ted,

I will start on it again tomorrow morning and follow your very good instructions.

It is a double fault issue...if not more. The belt was clearly broken and is now replaced. But, power is going to the motor and it is just not turning. So, corrosion or a connection(s) is now to be inspected as the motors should be fairly long lasting - without abuse..and my 1710 MkII was definitely never abused!

The Tom

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Gave one more try for tonight....

Post by Head Tomcat » 20 Jul 2009 02:06

...and I am still in the same position.

I checked the fuse on the PC power board and it is fine. I then removed the two black plastic connectors at the 3pm position and carefully cleaned around the connections...and then snapped them back into place.

The motor will for some reason not run...even though power is going to it. And, even when I manually rotate the large white plastic gear there is nothing happening to raise the arm. I think I am at the place where it must come apart and the raising mechanism must be looked at...and the cue button itself needs to be cleaned out.

Could you help me open it up now?

Many thanks!

The Tom

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Looking for some help...am back again in the shop

Post by Head Tomcat » 20 Jul 2009 16:47

Ted,

I think that two things are going on here with my 1710 MkII:

1. the motor is not working and it is due to some connection - or the motor itself - as power is definitely going to it.

2. the mechanical arm raising mechanism is also not working as I can easily spin the white plastic pulley...but nothing happens to the mechanism itself. There is something going on here.

Looks like I have done about everything which can be done without actually opening it up...and the time is nigh where that must now occur.

Can you help with instructions for getting it correctly opened up? I am pretty sure that once this happens I will quickly sort out why the arm raising mechanism is not working...and testing will show why the motor is not working.

Thanks!

The Tom

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Post by carlosfm » 20 Jul 2009 17:24

Hi,

I have the 1610 MKII and it has the same problem.
Actually, when I bought it (used) in the beginning of the 90's, it already had that problem.
It was the belt of the arm motor that was broken and changing it for a new one worked well for some months. Then it stopped working again.
I have gotten used to manual cueing and have no problems.
But I have opened the TT for other reasons several times (I even replaced all the electrolytic caps - a big task) and tried to drive the motor directly with a small PSU. The motor worked, it did move the arm. Inverting the polarity returned the arm to rest position.
Then the patience was lost - I wanted to hear some vinyl.
I have not found the patience to open it yet again and track that malfunction down.
I suspect it's the driver chips that drive the motor that go kaput. They are on a dedicated board at the right, under the arm.
Those kind of chips were used in the 80's-90's in RS-232 multiple serial communications ports that I worked with and I have replaced hundreds of those chips. They just burned out.

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Post by analogaudio » 20 Jul 2009 17:28

The instructions to open it up in the service manual cover it well, I can do no better, you simply follow the instructions and it comes apart. You have the instructions right there with pictures, I can't do better.

But there is a snag. Once you have disconnected the AC power terminals which is unavoidable and released the cable connectors which is also unavoidable the thing is without power and you can't see it run to figure it out.

Before attempting dismantling consider the risk of something getting damaged, either some small part could get crushed or bent out of shape, something could get caught up inside, the electronics are static sensitive.

Better to do some more diagnosing first. How confident are you that the CUE switch is operating for example? I have replaced faulty switches which have gone intermittent. You can simulate the switch press by using a wire jumper to bridge the two switch terminals.

To get inside and have things powered up and running is a difficult process. I have experimented with dismantling from the other direction, from beneath, that way everything stays attached to the metal chassis, but the motor board and arm come loose once the black plastic inner base is removed. You will need to support the metal chassis the right way up so the lowest parts don't scrape your workbench and get damaged, but at least this way you can operate everything to trouble shoot it.

To remove the black base leaving everything else intact you should remove six Philips screws that hold the feet in place, two have two, upper and lower, two have one each. Take out three black headed screws that hold the complete arm to the black base. take out four yellow finish metal screws that hold the motor spindle and drive board to the black base. The base should now be free and lift off. Be careful because everything is now loose inside, you have to pick it all up and turn it over onto some supports so you can experiment and watch. It is a pain to do this. Things can easily get damaged.

If you are good with schematics and the multimeter you shouldn't have too much trouble. The motor runs on either 5V or 12V, the 0.7 V you got isn't the normal drive voltage.

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Many thanks!

Post by Head Tomcat » 20 Jul 2009 18:01

Ted,

I am going to give it a shot over the next few days and will post what finally turns out. I am pretty confident it can be repaired correctly as I have the desire...some electrical knowledge...schematics....service manual....and sometimes a bit of common sense.

Thanks so much for giving me the information - and desire - to dive in and see what happens!

The Tom

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Post by Alec124c41 » 21 Jul 2009 02:06

Sussestion: set it on tall supports on a mirror.

Cheers,
Alec

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Post by analogaudio » 21 Jul 2009 18:11

carlosfm wrote

" I have not found the patience to open it yet again and track that malfunction down.
I suspect it's the driver chips that drive the motor that go kaput. They are on a dedicated board at the right, under the arm.
Those kind of chips were used in the 80's-90's in RS-232 multiple serial communications ports that I worked with and I have replaced hundreds of those chips. They just burned out."

I like the 'end of record' lift off feature which needs the arm motor to operate.

It is true that the Technics TTs use ICs, some unobtainable, however the arm motor drive for the 1600Mk2 and 1700mk2 use your basic low power transistor 2SD638 and 2SB643 for which equivalents can be found that do not degrade performance. In some cases original parts are available.

Personally I dislike the automatic muting when the arm is lifted and lowered, there is a delay before hearing the playback begin which I dislike so on my personal 1600mk2 I have disabled the automatic mute.

Ted

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1700mk2 arm motor functions

Post by analogaudio » 22 Jul 2009 00:50

1700mk2 arm motor functions

the arm motor is driven from a balanced active circuit with DC that reverses polarity and motor spin direction.

clockwise rotation of the motor and pulley raises the arm rest, the motor is driven with 8V yellow is positive and black negative

counter clockwise rotation lowers the armrest, the motor is driven with 5V black is positive and yellow is negative

Ted

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