Forging on ahead, I felt it was time to give this keyboard some new life.  The bushings were pretty much shot, and several were starting to crumble away – yielding the all too familiar snaggletooth keys and loud metal-on-metal action:

 

 

Getting the Four Voice’s keyboard assembly out involves excavating the synth from its integrated roadcase.  There are a total of six machine screws on the bottom of the tolex-covered enclosure that have to be removed, as well as the pair of handles on the rear of the unit.  The entire aluminum frame can then be lifted up and out of the wood enclosure.

The whole chassis by itself was a lot lighter than I had expected!  This thing is a real beast to lift, and now I realize how much the roadcase accounts for that.

 

Obie in the raw!

 

The Pratt-Read keyboard sits on a pair of stand-offs, and a series of machine screws secure the whole assembly to the enclosure’s aluminum base-plate.

Upon removal, I noticed another PCB hiding there underneath – mounted on spacers that appear to be JB-quik-welded to the underside of the keybed.  Just when I thought they couldn’t possibly have stuffed any more CMOS into this thing… =)

 

The harsh action and uneven keys are a result of the old rubber key bushings becoming brittle, to the point that many have started crumbling away.

 

The bushings can of course be replaced without disassembling everything, but I thought it best here to tear this keyboard down and really do it up nicely.  It’s a tedious job, but the end result is worth it!

Starting with the key-tops, I began stripping it.

 

Round-nose pliers work great for removing the key return springs – and it ensures the spring ends won’t get nicked or damaged by conventional pliers in the process.

Two different tension springs are used on the black and white keys, and they can be identified by color (red=white key, blue=black key).

 

The plastic j-wire clips need to be detached from their respective key actuators…

 

…and then the metal key frames can be pulled free from the keybed.  Note the thirty-plus years worth of crud, and the disintegrating key bushings.

 

 

Simply touching some of the old bushings caused them to crumble away!

 

 

Here’s the keybed after a thorough delousing and with new key bushings installed.  These were purchased from Vintage Vibe, and they came “pre-lubed” with the recommended Dow Corning 7.

 

Meanwhile, the keytops were soaking in warm water with dish detergent.  I used a small brush to scrub them down, rinsed, and let them dry thoroughly.

 

 

A cloth dampened with naptha worked wonders in cleaning the key frames.  Some keys had a bit of surface rust on the actuators, but this came off easily…

 

Everything was clean, and so began the reassembly.  Key frames went on first, and I used a touch of lithium grease on their fulcrum points to ensure smooth action.

There didn’t appear to be any triggering problems prior to this refurb effort, but I still gave the busbar and j-wires a once-over – using a swab dampened with DeOxit D-5 contact cleaner.

 

 

I have a bottle of this wonderful stuff called 3M Finesse-It II (mfg part number 39003) that I’ve used to buff out guitars, smooth out minor finish repairs on automobiles, get rid of scratches on beat-up rental DVDs that skip… you name it!

Prior to reinstalling the key tops, I had the thought of polishing them up with this compound.  None of the key tops were particularly rough, mind you, but a few decades of wear and hairline surface scratches left them looking kind of dull and tired…

 

…and the finishing compound more than fixed that.  The key tops look brand new now, and they feel smoooooth!

 

 

Some adjustment was still needed, as can be seen below:

 

The prongs on the keybed can be manipulated with needlenose pliers to adjust the lateral and vertical position of each key.

 

End result is a level keyboard with consistent action across its length.

 

With the mechanicals finished, I shifted my focus to the electronics.  It looks like this board handles the duties of decoding the key-presses (contains several 4028s and 4011s) and sends the resulting state changes over to the polyphonic keyboard module.

A tantalum bypass cap can be seen here:

 

That was refreshed with a similar value electrolytic, although I had to mount it on the opposite side of the board due to space constraints.

 

The CMOS on this board was socketed, which is great.  I’m planning to re-chip this before I put the synth back together.  Might as well, and save having to pull the case apart again down the road if the original CMOS (well past its life expectancy) bites the dust.

 

I took this opportunity to retrofit decoupling caps to each CMOS chip as well.  It apparently wasn’t a norm to do this back when these synths were built, but since CMOS can impart noise on the power rail when switching states its a good idea to add these.

 

 

And there you have it – good for another thirty-six years!  My next posts will cover the tolex enclosure refurb, mixer module and rear connection panel cleanup, the SEM and programmer module troubleshooting/repairs/calibration, and finally my new wiring to integrate the MS-1A sequencer and noise/s&h source.  (…oh yeah, and I’ll need to cleanup and re-cap that module too =)