keyboards 2

Got one of these working at last. Some re-wiring, a good scrub, remove some of the mods and a bit of guesswork.

 I can only assume this isn't how it left the factory. The rest of the Arp is beautifully wired, but this is shit.

 slightly less shit

 I assume this is an external input jack, it had been rewired so turning the switch connected +15V to ground. Decided it was not a useful mod and removed it. If anybody is able to supply photos or a schematic showing how this is connected, please comment.

 Again I don't know if this is standard or mods.

 This is the side panel on one keyboard. The pot and switch are not connected to anything. The other pot & circuit put a voltage onto the external jack, but are not connected to the keyboard other than sharing power supply. It seems unfinished or half-baked, bit of a theme with this synth.

Power connections rewired and heatshrinked.

keyboards

So these didn't work. Testing showed +9 to +15V on the -12V rail......yuck.
Inside was a bit hairy, with some interesting mods. One panel was obviously DIY, the extra output connectors are a complete mystery. The wiring and soldering is quite poorly done, really not up to the standard of the modules. There is so little info available on the keyboards.

 Doesn't really look stock, feel free to correct me. These are on both keyboards but only wired up on one.

 back view

 power connector, top is +15V, bottom middle is -15V, bottom right is gnd

 Arp for lunch

 the red & black wires go to the external input socket

 Pretty shitty job on these sub-modules

A nice short circuit between the +V and -V rails, took a while to find. Obviously a wire brush and a rewire are on the cards.

new power supply

Just letting this sit for a while

1005 Modamp

 nice early multiplier

1046 Quad EG

Nothing worse than a blown bulb on EG #4

 interesting technique to make sure the lens stays in place, must have been a stinky job

1016 dual noise / random voltage generator

This one has been modded, note the extra switch on the panel, and contains a tuning circuit. There is a 1964 tuning fork oscillator inside. There are pics of a similar item with its guts exposed on this page, scroll to the bottom.

 foam is crumbling away

 you can see the tuning fork in these pics, presumably the coils on either side of it pick up the vibrations.

 cans are TI 741s

 copper is well corroded

 Safely packed away.....bye!