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Vermona Synthesizer: Keyboard maintenance and calibration

Posted: Wed May 27, 2020 3:53 pm
by Synthfluencer
Hi there,
I am new to this forum but not new to synths & electronic music; bought my first synth (Roland D-10) in 1992; own a small home studio (wife calls it "the synth cave") and I'm as of late proud owner of a Vermona Synthesizer from 1983.

Edit: Yesterday a very kind person who - as I suppose - is a former engineer at Vermona sent me the service manual. It describes how the calibration works and from its technical description I learned that the "metal bars" simply providing the power for VCO and VCA. Thus usual rust removing techniques should be applicable.
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The synth is in pretty good shape, yet it shows some age marks. I gave it a quick cleanup and brought the crackling rotary pots back to life. The keyboard works overall quite well although some keys show a slightly tune instability. I suspect the corrosion (see attachement) on the "tubes" underneath the keys. There are two rows of those tubes, divided in several sections. Since the synth has two VCOs I guess these two are responsible for the control voltage given by the keys. Does anyone have a good recommendation how to clean these "tubes" (don't know if there is a better more technical term) without destroying a potentially existing resistor layer?
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Additionally; I am looking for a repair manual for this rare synth, at least some how-to showing the calibration of it. There are several calibration pots on the board inside but I don't want to play around with them not knowing the "calibration strategy" ;) Already found the owners manual and patch sheets on the manufacturers website but nothing looking deeper into the tech details.

Thanks for any hints!
Best, Synthfluencer

Re: Vermona Synthesizer: Keyboard maintenance and calibration

Posted: Sat Jul 18, 2020 1:55 pm
by upunkt
Hi,
I've been owning and servicing both a Vermona E-Piano and the Vermona Piano-Strings (still own the piano), both instruments seem to make use of the same technique as the Vermona Synthesizer regarding key/voltage flow. I had the impression that these bars are covered with silver. However, to get them polished I did not use dedicated silver polish paste but benzine that evaporates traceless. Reason is, I feared tiny scratches by polishing too much that in turn would collect dust or dirt much easier.

So take a piece of soft cloth (cotton e.g.), cut it to stripes 20 cm long and 2 cm wide, take tweezers and fiddle the clothe behind each section of the bars. I supplied the benzine with a q-tip and started polishing.

Make sure to have the synth disconnected since otherwise there is voltage on the bars and shorts can happen easily especially when using tweezers.

One more thing, the wires meant to make contact sometimes aren't straight enough or slightly deformed. Try to bend them so that contact really happens. Good luck!