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VCS3 RENOVATION PROJECT

 

 

I was very lucky to be able to buy an EMS VCS3 (mk II) and  DK2 duophonic

keyboard from someone in Australia (many thanks Greg!)  Whilst the DK2 is in excellent condition..the VCS3 was in need of quite a lot of attention as it had been languishing for goodness knows how many years in a school somewhere in Australia! Anyway I bought it

in non-working order as a renovation project and it gave me the opportunity of owning and playing this classic British synthesizer. A friend and fellow  EMS enthusiast James Gray in Adelaide arranged the shipping of the VCS3 to the UK..no small task (cheers James!). Finally it arrived safely and I was pretty excited to start the task of bringing this wonderful blend of art and science to life again!

 

In these pages I will describe the project with a hope that it will provide useful info for those people who already own VCs3’s/synthi A’s and whose units might suffer from some of the problems my unit had. Anyway if you have always wanted to see the insides of a vCS3 here we go!

 

 

First up here are some pics of the unit I bought..(AFTER making some cosmetic repairs!)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                            COSMETIC FACE LIFT

 

 The pics above show the unit after I had worked on the cosmetics a bit. When I first got it ..it was pretty dirty and needed a good clean. It looked a whole lot better after that..and I could see what things needed repair.

 

*Woodwork Repairs

 

The wooden case on the VCS3 is really pretty to look at ..and gives the synth its unique styling.

The wood is quite exotic..`aformosia’ as I understand. Anyway it’s a skilled job to make one of these cases ..mortice and tennon joints everywhere and angles to get right. The case on mine had suffered a bit with most of the joints needing re-gluing. This was the first thing I did..using wood glue to reset all the joints. There was a small crack along one side, near the point where the speaker holes are located. This is a well known weak point on VCS3’s so I wasn’t too surprised to find one. Carefully opening the crack slightly and inserting gluing, its possible to get an almost invisible repair.

After re-seting the joints..the whole unit become very solid. Only fiddly part was getting

the front panels to fit into the slots that hold them in place..but eventually I did it.

 

The major woodwork repair was yet to come! The unit had lost its wood top piece at some point in the past but luckily Greg (the person I bought it from) had obtained a piece of bare wood (aformosia?) that was a very close match to the existing woodwork. This came with the synth as a cut rectangular block. The task remained to cut this as precisely as possible, with the correct angles to fit perfectly onto the joints on the top of the vertical sides of the unit.

I did this ok..what remained was to route out the slots for the joints and two long thin slots

which take the front aluminium panel and the rear wood panel. I found this a bit tricky..but using a drill press with a router bit finally got the job done in a day. The results are pretty good to look at. The new wooden top blends in very well with the existing wood.

 

Next I wanted to re-finish the lovely aformosia! There were a number of scratches/scuffs etc on the wood that is typical of use over 25 years. Using very fine wirewool ..I gently removed the old finish and with it these scratches. There remain a couple of dings here and there which will require attention ..but these could wait until I got the synth working.

When I finally got the finish I wanted..I then decided I wanted an oil satin-sheen finish on the wood. A good oil to use is tung-oil based ‘Antique Oil’. The technique to getting a satin smooth finish with oil depends on the wood you are working with. The bare aformosia has some open grain

which would normally prevent satin finishes with oil. To remedy this ..I worked the oil into the wood using the very fine wire wool. The idea is to produce a paste between the oil and the fine woodust that fills any remaining open grains. After several coates of oil (leaving 1 hour between each coat) I got an excellent satin sheen on the wood..Great!

 

 

*Knob cap replacement                          

 

Some of the silver coloured knobcaps were scratched so rather than replace the whole knob

I used some of the caps I had on the knobs I bought for my synthi A project. I had often wondered

whether these knobs (made by CLIFF COMPONENTS in the UK) were identical to those used on synthis..well now I know the answer is yes! Anyway I had exactly the satin silver coloured caps required to match the others on the VCS3. The knobs used on the VCS3 are 1/4” spindle type..unfortuantely mine were 6mm type! Not to worry..just carry out a cap transplant!

To remove the caps you need to drop the knob in hot water..wait a couple of minutes and then the glue softens enough so you can prise the cap off (carefully) with a modelling knife. A quick switch over of the caps and regluing them gives you a set of pristine silver knobs.

The coloured ones would be more tricky ..as Cliff don’t make them anymore. Luckily those on my VCS3 are in pretty good nick.

 

 

 

Electronics Repair

 

 

OK having sorted out most of the cosmetics (and certainly the VCVS3 looked a whole lot better for it), time to figure out what was working and what wasn’t ...

 

The unit powered up ok ..ie the red neon light lit up on the front panel, but no sounds at all. First thing I checked was whether the +12v and –9v rails were working. A quick test showed that both were faulty.  On the VCS3 there are three main circuit boards (labelled A-C) which contain all the circuits corresponding to the various modules. Here is a quick list of what board contains what:-

 

 

BOARD A

 

*    Power regulation circuit (+12/-9V )

*    Voltage controlled output amplifiers (channels 1+2)

*    Tone controls on output channels (1+2)

*    Voltage controlled Reverb

 

 

BOARD B

 

*    Envelope Shaper

*    Filter

*    Input channel amplifiers (1+2)

*    Ring modulator

         

 

BOARD C

 

*    Oscillator 1  (sine+ramp)

*    Oscillator 2  (square+triangle)

*    Oscillator 3  (square+triangle)

*    Noise generator and meter amplifier

 

         

 

* BOARD A REPAIRS

 

Clearly the power regulator wasn’t working in my case. After checking I found that one of the

onboard power transistors had clearly overheated in the past and failed as the plastic transistor

socket it was mounted on had fused to the metal can! I replaced this and a few other dead transistors (broken legs) I found on the board. Also I replaced some electrolytic caps that were clearly leaking. After powering up..I found I now had +12v/-9v supplies. Two cermets on Board A allow you to trim these voltages fairly accurately. One important point to note here..neither of the 2 metal can power transistors on board A had heatsinks on them when I checked the board. One of them runs VERY HOT and my guess is sometime in the past, these heatsinks had come off and caused failure of the PSU. With heatsinks mounted (see pic below) one of the transistors runs hot but remains stable..without it it will fail! Make sure these heatsinks are always fitted before powering up. On mk1 units I believe there is a slightly modified psu design..but still there are heatsinks on some of the power transistors. The other ‘repair’ I did was to replace all the old openframe cermets on all 3 boards with modern encapsulated types..much better for accurate tweaking later.

 

After repairs ..here are some pics of Board A :-

 

 

UPPER ½ OF BOARD A SHOWING HEATSINKS ON THE TWO POWER TRANSISTORS (upper/left)

 

A new MFC6070 chip (6 legged creature at bottom right) was used as the old one had blown.

 

 

photo below  shows  the lower ½ of Board A.

 

 

 

 

 

 

*            BOARD B REPAIRS

   

    When I checked out Board B I got a bit of a surprise. The ringmodulator circuit was not quite the classic EMS design I was expecting. Rather only part of the circuit was ..but then instead of the matched transistor pair and transistor array chip (TAB101) someone had stuck a MC1496 run of the mill balanced modulator chip in there! I am not sure how this would have sounded in anycase I will never know ..since I rebuilt the circuit to the original EMS spec.

I had already built one before in my synthi A clone. It’s a really nice ring modulator. Anyway I used an AD, MAT-02 precision matched pair and a CA3046 transistor array instead of TAB101.

This required some pin swapping as CA3046 has different pinout from TAB101. I used a small piece of circuit board to achieve this rather than have a mess of wires everywhere (see photo below).

 

 

UPPER ½ of BAORD B AFTER SOME REPAIRS. NOTE THE METAL CAN MAT-02 NPN PAIR AND THE CA3046

ARRAY IN THE RINGMOD section

 

 

 

 

This shows the lower ½ of BOARD B

 

 

 

 

*            BOARD C REPAIRS

 

Most of the transistors were replaced on this board and trim pots updated to modern closed type.

Also supermatches transistor paits LM394CH used on all 3 VCO’s.

 

 

This shows the upper ½ of BOARD C

 

 

 

 

 

 

 

This shows the lower ½ of BOARD C

 

 

 

 

 

This shows a view of the rear of the front panel. All the pots were replaced with carbon type of almost exact same form factor.

 

 

 

 

This shows the view of the lower panel from below. I have since replaced all the old electrolytic capacitors in the power supply. The reverb tank visible below turned out to work ok..just the driver chip MFC6070 needed replacing.

 

 

 

 

 

 

 

 

 

 

 

                                                   Digitana, 28/11/08