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MiniKorg Power Supply

MiniKorg-700S

MiniKorg-700S

MiniKorg-700S

MiniKorg-700S

To repair synthesizers, it helps to be part electronics technician, part metal worker, and part wood worker. In the case of this MiniKorg-700S, good wood working skills came in handy.

Missing Wooden End Caps

Missing End Caps

Missing End Caps

Missing End Caps

Missing End Caps

Before even turning on the MiniKorg, it was apparent that it had some cosmetic issues. The most obvious one was a lack of wooden end caps. At some point in the past, somebody removed them, and they were lost.

This was the last part of the repair that I completed. But it was the first thing that I started.

I wanted to get a nice glossy finish on the end caps. This took several evenings of applying stain or varnish, and letting it dry overnight. While the end caps were drying, I worked on the electronic issues.

Cutting New End Caps

Cutting New End Caps

Cutting New End Caps

Cutting New End Caps

New End Caps

New End Caps

New End Caps

New End Caps

I also needed to mill out some grooves in the wood, so that the end caps would lay flat against the synth, and not stick out due to protruding screws and panels. The end caps don't actually touch the table, as there are rubber feet on the body of the synth.

In the end, the new end caps looked so nice that it took the eye away from some of the other scratches and dents in the MiniKorg.

Power Supply Re-cap

Old Power Supply Capacitors

Old Power Supply Capacitors

Old Power Supply Capacitors

Old Power Supply Capacitors

New Capacitors, Lined Up And Waiting

New Capacitors, Lined Up And Waiting

New Capacitors, Lined Up And Waiting

New Capacitors, Lined Up And Waiting

As with most synths this old, the power supply caps were overdue for replacement. It can't be stressed enough how important this is, as if the capacitors fail, they can cause the power supply to fail. This in turn can send high voltages to the other parts of the synth, causing more damage. It's just easier to replace the capacitors when you have the opportunity.

From the looks of the dirt and crud around the old power supply board, it looks like this MiniKorg is also due for an internal cleaning!

Switch And Fader Cleaning

The only other issues remaining were all related to dirty switches and faders.

The MiniKorg has a large number of toggle and rotary switches on the front panel. Internally they are oriented so that any dust or dirt that falls through the keyboard will land directly on the switch contacts. A careful cleaning of the switches (and faders) brought everything back.

Future Proofing the Design

Old Transistor Array In A New Board

Old Transistor Array In A New Board

Old Transistor Array In A New Board

Old Transistor Array In A New Board

While looking around inside of the synth, I came across this nice example of future proofing.

Shown in this photo is a transistor array, packaged in a TO5-12 (the round metal can with 12 legs). Around the time when this synth was manufactured (1974), these types of packages were being replaced with the familiar Dual Inline Packages (DIP).

You can see from the legend on the circuit board, that the designers were anticipating switching over to the new DIP packaging.

7 comments on MiniKorg Power Supply

Mark Adame
My 700 has a few keys that drift in pitch akin to a mosquito buzzing. Not sure what is causing this but I'd like to try and clean the key contacts just as a maintenance procedure. I'm not much of a wrencher but I did open her up and remove and clean all the keys and carefully blew out the ... Read More
December 19th 2015 21:40 EST
Nate
Great work on this great synth!
You don't happen to have measurements for the wooden side panels still, do you? I need to get some made.
November 2nd 2016 10:55 EDT
Keith
Hi Nate.

Sorry, I don't have the MiniKorg in my studio any more, so I don't have the dimensions for the end-caps.

-Keith
November 3rd 2016 19:59 EDT
Carlos M
Did you already receive the panel measurements?
August 24th 2017 08:25 EDT
Pete
Hi Keith, I have a Mini Korg 700s in pretty good overall condition, but has been in storage for several years. I am looking for someone to restore it - with a view to selling it. Would you be interested in taking this on? It's electronics restoration, not really the cabinet ends or body. I can ... Read More
April 30th 2018 19:14 EDT
Keith
Hi Pete,

Sorry, I have too many projects on the go right now to take on a restoration job. Try looking for a local synth repair tech. The Mini Korg is rather basic in design, and most techs should be able to help you out.

-Keith
May 1st 2018 09:58 EDT
Carlos M
Hello, so did you replace the TO5-12? I'm thinking you left it alone but just wanted to mention it in your blog. If you did replace it - what was it replaced with?
November 5th 2018 09:54 EST
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