Dual CS 508 speed adjustment alignment problems

twice the fun
Post Reply
vinylcollector
Canada
Posts: 3
Joined: 17 May 2019 05:09

Dual CS 508 speed adjustment alignment problems

Post by vinylcollector » 17 May 2019 19:27

First time poster.

The 33/45 speed adjustment dial went on my Dual CS 508 turntable. The little plastic tab on the bottom of the dial broke. I have 2 new old stock Dual replacement parts of it. So while I had it apart cleaned and oiled the motor, and adjusted the pitch belt assembly properly.

The turntable belt I think a few years old but from William Thakker. After putting the speed adjustment knob in, it does not want to switch the speeds properly. It will go from 45 to 33 no problem. But to go from 33 to 45 if I move the lever really slow it will switch, but moving it faster will not switch. There's a flat metal leaf spring bottom side, that bends when you switch the speed, and it presses and moves a lever that makes the belt guide move the belt up or down on the vario pulley. I'm guessing something is out of alignment? or something needs cleaning re-greasing?

The belt guide assembly has a screw to move and shift the assembly some. The service manual does not have any info about re-assembly and aligning the speed selector, and what parts need to be oiled/greased for it. Could the metal leaf spring be worn out? Here are some pictures I have found of what I am talking about.

Thank's
Attachments
Dual CS508 speed assembly3.jpg
CS 508 speed assembly
(88.81 KiB) Downloaded 63 times
Dual CS508 speed assembly 2.jpg
CS 508 speed assembly
(91.03 KiB) Downloaded 63 times
Dual CS508 speed assembly.jpg
CS 508 speed assembly
(182.37 KiB) Downloaded 64 times

mrow2
long player
long player
United States of America
Posts: 3413
Joined: 25 Aug 2010 03:05
Location: San Clemente, California

Re: Dual CS 508 speed adjustment alignment problems

Post by mrow2 » 18 May 2019 06:07

I don't believe I worked on a 508 but on other, older models the symptom of belt not switching speeds (often one way but ok on the other) was an indication of a belt just slightly too tight. But in this case, the belt age of a few years might seem to contradict that. I had found that a slightly less tight belt would be the answer. This also could be something related to the pulley (referred to as "taper bush," part 15 and the cone-shaft inside it) and maybe the chrome plating is a little dirty or has some corrosion on it, not adjusting smoothly, something like that. Speed change issues are frustrating to fix but if you can just be sure all the parts are functional and moving properly it might eliminate some possibilities. I rarely hear of a Thakker provided belt as being too tight. Whatever you do, don't try to use a generic belt, they rarely work well for Dual. Make sure the pulley is ok and don't bend the splines; just be sure it moves the way it should, and is clean.

vinylcollector
Canada
Posts: 3
Joined: 17 May 2019 05:09

Re: Dual CS 508 speed adjustment alignment problems

Post by vinylcollector » 18 May 2019 16:03

Thank's
The pulley and cone shaft are working fine. I cleaned the cone shaft awhile back . I need to check the height of the pulley which I've never moved/adjusted before.

But with the belt off, there is a little tiny bit of play in the dial when on the 45 spot. (none on the 33 spot) wiggling the dial back and forth at the 45 spot the belt guide will move up and down. So this seems to be where the problem is. Will take it apart again tonight.

mrow2
long player
long player
United States of America
Posts: 3413
Joined: 25 Aug 2010 03:05
Location: San Clemente, California

Re: Dual CS 508 speed adjustment alignment problems

Post by mrow2 » 18 May 2019 18:22

Perhaps carefully remove the toothed belt and re-install, in a different position? At any rate, you are looking at everything I would be. It's a crazy design; these guys were obsessed with keeping things as mechanical as possible when the other side of the world was making it all "fly by wire" (electronic switching) with switches, pots, ICs, DC motors, wiring and such. The electronics bring along their own problems but often were easier to resolve and mostly it was a matter of keeping switches and pots clean; a more pleasant task at times than scratching one's head bald in a stare-down with a dodgy Dual switching mechanism. Yours may come down to whatever slight difference there is between the original (and unavailable) ground Dual belt and the made-as-close-to-spec belt Thakker and also a vendor in the US offers. On the latter, if you end up ordering another belt you could at least look at Turntablebelts.com and see what he is offering; I never had any trouble with those.

Minstrel SE
senior member
senior member
Posts: 498
Joined: 19 Aug 2013 19:35

Re: Dual CS 508 speed adjustment alignment problems

Post by Minstrel SE » 23 May 2019 18:23

Hi yes its not a million miles away from the 505 design of speed changing.

As mrow says its a crazy design in a way....sort of clever but crazy and not really designed for users to be servicing or dabbling with it.

I wondered why they couldnt have more of a fixed link than the metal bar spring which sits in the grooves. The bar seems to sit in so delicately that you sometimes wonder how it even stays in place

That said all parameters take a bit of study. tight belts or a spindle which may not be at the correct height. a splayed pitch control mech, sagging motor if its on rubber mounts

A quick flick of the speed control switch is never really a good idea and I find a more positive holding while turning is best.

It could be several factors why the belt doesnt move over. A Thakker belt is good so be careful of no name generic belts as they are often not the right size.

I dont switch it over that much as I only have a few 45s. When its all set up it does work. its such a precision mech that age and wear is not particularly kind to it. I think the real flaw in the design is too many factors are linked to its smooth running.

All the best with it
Martin

vinylcollector
Canada
Posts: 3
Joined: 17 May 2019 05:09

Re: Dual CS 508 speed adjustment alignment problems

Post by vinylcollector » 29 May 2019 21:54

Thank's for every ones help. I decided to order new parts for the speed assembly including that flat spring. And they just arrived today. That will rule out any worn parts. I will put them in on the weekend.

Post Reply