Sunday, November 8, 2009

Oberheim Matrix-6

This is a problematic one. Of the three synthesizers I bought at the same time, it is the second of the two faulty ones (the other being the Poly-61, the working one the JX-3P).

You can't really miss the broken off key. I still can't imagine how one manages to do break a key but I guess clumsyness or flimsy keyboard stands are two major "players"...

The surprise is the second broken key which looks intact at first but if you touch it you notice it will give.

Maybe all this needs is some proper treatment with superglue.

But, now to the two main points:
1 - The guy who sold it said it's a 120V-machine.
2 - the guy who sold it said it only makes a constant tone when powered on.

To be able to fix problem 2 I first have to be able to power the thing. The guy also mentioned that he had a faint memory of there being a possibility to switch mains voltage inside the unit (there's no convenient switch on the back) and he said the maaaaybe this had already been done but the unit was not re-marked for 230V.
In any case I needed to open it up and look at it, so I did.
I didn't see any obvious way of switching the voltage, but the transformer gave me a very welcome clue.

Most obvious thing would be the sticker saying "100V/230V" over the "41V 30VA".
Interesting. Now, why would you need 4 wires on the primary side? Hmm..
I looked at the service schematics for the Matrix-6 and sure enough it looks like one wire is marked neutral and three different voltages.
A closer look at the fuse board which sits on the inside of the front panel (in the lid so to speak) reveals that the fuse is connected and neutral to one wire while two wires are not connected.
I looked carefully and it seems as if I remove the 1A fuse for the 120V wire and put a new fuse holder for the 230V wire and put a 500mA fure there I should be good to go!

Red connector comes from mains power and power switch. White connector goes to transformer. See the big fuse at the bottom. It connects the mains power to one wire on the transformer. For the wire marked as 200-something on the schematic (I think it says 230V) I need to place a fuse holder in the empty room just to the right of the white connector.

After talking to some guy in a forum he looked in his Matrix 6 and confirmed that this was really the case. Excellent news!

One thing that scared me was that although there was an empty place for an IC socket, which there sometimes are, there was an actual empty socket as well. However, the guy on the forum said that the same socket on his unit was empty as well, so that was reassuring.

Once I modify the fuse board to use 230V mains I should be able to at least power the Matrix 6 up and then see what could be wrong with it.

At least all the CEM3396 chips are in it :)


  1. Hi Peter, could you tell me what I need to do to open the panel on my Matrix 6 keyboard? Thanks!


  2. Hi.
    I don't remember exactly but there are three screws on the left and right sides of the synthesizer, about where you'd grab it when you carry it. Unscrew those six and your should be able to flip the panel back.

    Actually I just tried which screws worked. Screws on the underside that are not immediately at the back usually hold circuit boards and keyboard in place so don't loosen them until you got the panel opened.

    Be extremely careful with the mains power though. Don't keep it open with the power cord connected to the wall socket unless you REALLY know what you are doing!

  3. hi peter.
    so, to set the matrix to 220v instead of 110v. i need to put a new fuse holder in the empty room. is that all?. thanks.

  4. Hi, yes as far as I remember that's all I had to do.
    Of course you might want to measure the voltage on the cable before you connect it to the rest of the unit.
    It should look like this:

    Good luck!

  5. hi peter!. can you give me your email? i want to send you some pictures, front and back of my fuse pcb, it looks a little bit different. it seems like originally was 220v and someone has modified it to 110v... you can maybe help me.

  6. Thanks! It works perfectly on Matrix 6R also. Just finished this conversion.