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 Forum index » Instruments and Equipment » General Discussion
Roland CMU810 (DG Compusynth)
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Ayab



Joined: Oct 27, 2015
Posts: 180
Location: London, UK

PostPosted: Tue Oct 27, 2015 4:57 am    Post subject: Roland CMU810 (DG Compusynth)
Subject description: Replacement potentiometers
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Hi

Am new to the forum here and so a friendly hello to you all Very Happy

I need to replace two of the sliders on my Roland CMU810 - can anyone here point me towards the correct part?

All the best


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DrJustice



Joined: Sep 13, 2004
Posts: 2114
Location: Morokulien
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PostPosted: Tue Oct 27, 2015 5:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

It's a rare synth and the service manual is not available it seems, so I'd measure the dimensions and resistance (the resistance is probably printed on the of the existing slider) and then find a matching part, e.g at Digikey, Slide Potentiometers.
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Ayab



Joined: Oct 27, 2015
Posts: 180
Location: London, UK

PostPosted: Tue Oct 27, 2015 5:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for reply Doc and that is good advice. Will do.

Was even thinking I may need to make a break out box for some other sliders. I can also take it to Japan with me next year when I go to Tokyo and maybe there will be a guru there somewhere Cool

I really like this forum - I left this question at Muff Wiggler and no answer for a couple of weeks. I also found all the info for my SN Voice build that I needed.

Edit - Here are some pic's (embarrassed at how dirty it is!)

There are no printed values. The photo on the back shows the pattern of the soldering underneath the slider - 5 joints: from the three at the bottom (in terms of slider movement & at 8mm on scale) to the small one at the top (at 32mm on scale).


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DrJustice



Joined: Sep 13, 2004
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Location: Morokulien
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PostPosted: Wed Oct 28, 2015 12:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Don't worry about the dirt; "ancient" electronics tend to look a bit like that Smile

The attached image shows a matching mounting arrangement. It's fairly standard. You can see a similar mounting arrangement on this ALPS potentiometer.

As for the resistance value, if it's not printed on the part, you'll have to desolder and measure the resistance of the track. Ref. the ALPS link above for the pins to measure, i.e. 1 and 3. Then, to find out if it's a linear or logarithmic potentiometer, set the lever at the half way point. If the resistance between 1 and 2 is the same as for between pins 2 and 3, then it's a linear pot (taper type B), if it's significantly different it's a logarithmic pot (taper type A).

When this as well as the precise dimensions and mounting points are determined, it's time to search the net for a replacement part. You can try e.g. DigiKey and RS, or you can go to the manufacturers sites (ALPS, Bourns etc.) and find the part, then hit the net to find a reseller. If you have a Maplin outlet within reach, they might be able to help you.

For what it's worth, here's the MC-202 manual. Allegedly, it has the same synth circuitry, so you may be able to use it to verify your findings (the mechanical dimensions may be different). On page 9, you'll find the relevant schematics. The ADSR envelope potentiometers are: VR17 (250k log), VR18 (1M log), VR19 (100k lin), VR21 (1M log).


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Ayab



Joined: Oct 27, 2015
Posts: 180
Location: London, UK

PostPosted: Thu Oct 29, 2015 4:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Doc - thank you so much and it will be thanks to you that I can hopefully breathe life back into this synth.

Btw I really appreciate you taking the time to explain the details to me. This forum rocks!

(n.b. Will be giving it a careful clean with something safe!)

Sending you good vibes and best wishes from London.

Edit - the link to the MC202 manual is all mad visual black and white shroomed out stuff! Or I have lost my mind (again).
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DrJustice



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PostPosted: Thu Oct 29, 2015 5:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

You're welcome Smile

Hmm... the MC-202 manual link works fine here, but here's an alternative, not as good quality but it'll do the job.
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Ayab



Joined: Oct 27, 2015
Posts: 180
Location: London, UK

PostPosted: Fri Oct 30, 2015 7:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Doc

Tusen takk!

That is really useful and especially as am seeing my synth tech friend this evening and am going to consult him on desoldering the sliders. As I don't have a heat regulated iron or desoldering station.

Out of interest do you specialise in Roland gear as a tech or are you more a musician?

Enjoy your Friday evening and weekend - all the best.
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DrJustice



Joined: Sep 13, 2004
Posts: 2114
Location: Morokulien
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PostPosted: Fri Oct 30, 2015 12:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Not a Roland specialist, just an enthusiast maintaining my own gear and taking joy in sharing with fellow enthusiasts, as we do on the forum (also done a bit of electronics and embedded systems professionally, but I'm here in my capacity as a synth/gear and music nerd Laughing)

Best of luck with the restoration!
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