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Problem with turntable on SJT 100

 
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Moonie



Joined: 25 Nov 2017
Posts: 25

PostPosted: Tue Nov 28, 2017 8:24 am    Post subject: Problem with turntable on SJT 100 Reply with quote

Hi, again. New member Moonie here who just got some players and bunch of discs. We tested out the players, SJT 90 works just fine, but the better player, SJT 100, turntable just wobbles back & forth like it's got some power to it, but will not spin up. My husband thinks it's something to do with the electronics, and said it was a direct drive turntable. Any ideas on this? Crying or Very sad
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Moonie



Joined: 25 Nov 2017
Posts: 25

PostPosted: Tue Nov 28, 2017 8:57 am    Post subject: Reply with quote

I forgot to mention that we could find no information on this issue in the CED player repair section of CEDmagic.
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Moonie



Joined: 25 Nov 2017
Posts: 25

PostPosted: Sat Dec 02, 2017 7:54 am    Post subject: Reply with quote

So does nobody know about or never had this same issue? Maybe someone can point us to someplace to find out more about it? Thanks!
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dumbchemist



Joined: 27 Oct 2011
Posts: 411
Location: Central New York

PostPosted: Sat Dec 02, 2017 8:28 am    Post subject: Reply with quote

I have never had the problem you describe. Maybe the service manual can aid you::


http://manuals.lddb.com/CED_Players/

Hope this helps.
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Last edited by dumbchemist on Sat Dec 02, 2017 11:13 am; edited 1 time in total
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jsdspif



Joined: 16 Jan 2016
Posts: 119

PostPosted: Sat Dec 02, 2017 9:29 am    Post subject: Reply with quote

I was just going to post that link. I would say download the service manual and read thru it. It has a wealth of info that really should be read thru and also has vital info on opening the player and all work that may ever be required. May just be the turntable shaft needs some lube. There is also a small steel disc that is underneath the turntable shaft and it's possible that disc could be missing and that would make the turntable be too low and it's scrubbing underneath the turntable.
I'm not a fan of either of those players. Besides not being stereo (which isn't a big deal for some people) they also have no rca jacks for audio and video output, so they are not easily hooked up to a modern tv that only has a digital tuner. They would be good units to get started in repair of ced players for just the basics where if you do screw something up it's not a big deal, because either of those players in pristine perfect working order are still not very desirable and I'm thinking no one would be interested in purchasing one or if they did they probably wouldn't be willing to pay much more than $20 or so if they have to pay to have it shipped on top of that.
First and foremost though, i'd say download the manual, read it and maybe read it again then start in on troubleshooting of the unit. If you were to get it to the point where the turntable appears to be rotating properly that would probably be the time to send each cartridge to CEDatum for cleaning and inspection (which is free) and they will advise you of any work required to the cartridges to get them to proper working order (which the repair process costs money) but the initial cleaning and inspection is free of charge. Good luck.
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Moonie



Joined: 25 Nov 2017
Posts: 25

PostPosted: Sun Dec 03, 2017 9:08 am    Post subject: Reply with quote

My husband did read that manual, but says the issue isn't discussed in there, nor is it one of the issues mentioned here according to him. He's pretty good at repair of most stuff, and what he said is that it is an issue with the electronics of the turntable. I told him to join and post it because every time he describes it, I get lost. Hopefully I can get him to do that soon!
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cbertra2



Joined: 29 Dec 2004
Posts: 179

PostPosted: Sun Dec 03, 2017 9:16 am    Post subject: Reply with quote

If the turntable is wobbling from side to side such as tipping back and forth as it is rotating then it has to be a mechanical problem. If you mean the turntable is rotating back and forth then it's an electrical issue.
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jsdspif



Joined: 16 Jan 2016
Posts: 119

PostPosted: Sun Dec 03, 2017 9:37 am    Post subject: Reply with quote

if possible he could take some video of it and post it to youtube. It's possible someone may be able to diagnose the problem if they were to see it "in action".
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Moonie



Joined: 25 Nov 2017
Posts: 25

PostPosted: Sun Dec 03, 2017 5:55 pm    Post subject: Reply with quote

cbertra2 wrote:
If the turntable is wobbling from side to side such as tipping back and forth as it is rotating then it has to be a mechanical problem. If you mean the turntable is rotating back and forth then it's an electrical issue.


Moonie's husband here. That latter issue what it is doing, not really "wobbling" as it does not actually spin up. It does a back and forth motion like being pulled one way and then the other in a pretty consistent quickly cycling time frame, not sure if it's somehow coinciding/cycling with the 60 cycle current, but it definitely has something to do with the current to the direct drive not sequencing properly to spin the turntable in one direction only.

The schematics in the manual show a sort of 4 pole current switching sequence which I would assume pulls the "magnetic" disc base in a switching series that causes it to be spinning clockwise in a specifically timed rotation of 450 RPMs, as I understand it. Since it only "jerks" back and forth, I suspect this is what is out of whack, but don't know if it's due to some part on the board, or an issue with the motor windings, or bad contacts somewhere?
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cbertra2



Joined: 29 Dec 2004
Posts: 179

PostPosted: Mon Dec 04, 2017 4:14 am    Post subject: Reply with quote

If it is an AC synchronous motor it could be a bad starter capacitor.
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jsdspif



Joined: 16 Jan 2016
Posts: 119

PostPosted: Mon Dec 04, 2017 7:01 am    Post subject: Reply with quote

I don't know all the terminology without looking in the manual,but, can the turntable be rotated by hand and if so how does that act. You'd have to manually advance the 3rd reduction gear (not sure if that's the gear, that's where the service manual comes in). with your finger and that causes the rod that prevents the turntable from spinning to drop down below the turntable so it is able to spin. It should spin quite easy and continues to spin. It's not like a belt drive where there is resistance , it's pretty free flowing. I'm just wondering if something mechanically is preventing it from rotating because I think it doesn't have a whole lot of "strength" to it's rotation, so if there was enough mechanical problem it could prevent it from beginning it's rotation. I'm not sure but sometimes the small steel hardened disc at the base of the turntable shaft somehow "escapes" and then sticks to the magnetic band inside the I.D. of the turntable. I do not know but maybe that scenario would create this type of problem.??
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Moonie



Joined: 25 Nov 2017
Posts: 25

PostPosted: Mon Dec 04, 2017 7:43 am    Post subject: Reply with quote

Sorry, that's not it, the turntable spins freely on its own when no power is supplied, but thanks for trying to be helpful.

I believe it is as CBertra2 stated, a bad starter capacitor, or otherwise another issue in the electronics. I've seen such issues before in AC motor windings where the motor cannot get the initial spin going due to bad starter capacitor, and they just sit and hum at 60 cycles. Since this is a free-flowing direct drive turntable, no real resistance, it would make sense that it would cycle or vibrate back and forth in a regular pattern due to this.

My knowledge of electronics is limited, as I'm a mechanic, and mechanically oriented, but I'm going to look over those schematics more closely and see if such a capacitor is listed and an easy thing to replace. It won't hurt to do a disassembly of a player anyway that isn't working right as a learning project.
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SelectaVision420



Joined: 25 Mar 2012
Posts: 1325
Location: Hartford

PostPosted: Tue Dec 05, 2017 6:36 pm    Post subject: Reply with quote

here is what i have heard about the " turntable to and fro wobble " from another member on here...

this problem is caused by a problem in the turntable servo electronics.

1) on page 44 of the manual locate IC U5902 ( A Quad Op Amp ) check the voltages on the IC against the voltage chart on page 27. if the IC is bad it usually shows it in the load position ( note this IC is used in several locations on the player. it will be labeled 754-1 RCA improved the reliability of this component as the 754-3 CEDatum may still stock these.

2) check the waveforms on pins 21 and 22 on IC U5901 (page44) the HE1 and HE2 detectors on the PW motor board may be bad if the waveforms are not correct.

3) there is a small possibility that IC 5901 is bad or one of the motor driver transistors close to IC 5902
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Moonie



Joined: 25 Nov 2017
Posts: 25

PostPosted: Thu Dec 07, 2017 10:53 am    Post subject: Reply with quote

Well, that looks like the right page for it, but I could not find IC U5902. 5901 is obvious, not 5902. Found U5902A, whatever that is, and saw 4 different driver amps for the turntable, I suppose one for each of the four windings shown?
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SelectaVision420



Joined: 25 Mar 2012
Posts: 1325
Location: Hartford

PostPosted: Thu Dec 07, 2017 1:54 pm    Post subject: Reply with quote

Moonie wrote:
Well, that looks like the right page for it, but I could not find IC U5902. 5901 is obvious, not 5902. Found U5902A, whatever that is, and saw 4 different driver amps for the turntable, I suppose one for each of the four windings shown?


correct each of the 4 windings for the turntables direct drive are individually driven by separate amps, it is possible something went bad within one of the amp circuits...

U5902 is the Integrated Circuit for the turntable drive, there is a u5902A, B, C and D. a being test point 5901 and b being TP5902 c being 5905 and d being 5906 which i think are the test points for the turntable drive itself. also the IC voltage charts are on page 29 in my paper skt 090/100 manual.

as for the driver amps for the turntable it appears that there are 12 transistors, 8 npn and 4 pnp's one may have gone bad. another thing you can do is test the turntable drive field winding's for open circuit

i hope that helps
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Moonie



Joined: 25 Nov 2017
Posts: 25

PostPosted: Sat Dec 09, 2017 8:58 am    Post subject: Reply with quote

An interesting way to design a direct drive turntable, making the turntable an integral part of the motor itself. I suppose for better RPM control, or more likely due to the CED needing a capacitance voltage supplied separate from any other interference. Laserdisc turntables are apparently directly connected to their drive motors since they need no capacitance charge.

I will test the windings for continuity, seems a good first option. I still could not locate IC U592 on that page however. Maybe it will be obvious when looking at the board, don't know.
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SelectaVision420



Joined: 25 Mar 2012
Posts: 1325
Location: Hartford

PostPosted: Sat Dec 09, 2017 3:45 pm    Post subject: Reply with quote

Moonie wrote:
An interesting way to design a direct drive turntable, making the turntable an integral part of the motor itself. I suppose for better RPM control, or more likely due to the CED needing a capacitance voltage supplied separate from any other interference. Laserdisc turntables are apparently directly connected to their drive motors since they need no capacitance charge.

I will test the windings for continuity, seems a good first option. I still could not locate IC U592 on that page however. Maybe it will be obvious when looking at the board, don't know.



for some reason im under the impression that IC u5902 is the collective name for the whole turntable motor control section? (u5902 a-d)
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kitchensynch



Joined: 24 Feb 2013
Posts: 904

PostPosted: Mon Dec 11, 2017 6:09 pm    Post subject: Reply with quote

One thing I've noticed, in the case of some phonographs at least is that in the case of phase locked loop speed controls when the circuit goes out of whack the table will adopt a spin frequency much higher than 60 hz (70-90?) I this case I have to wonder what the speed of the turntable actually is and if it's well out of spec would that cause it to lose the signal or something?
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