I recently purchased an Oberheim Matrix 1000 analog synth in “excellent” condition from someone on Ebay who had good feedback.
Upon receipt of the unit and to my dismay, the unit could play only three voices out of six. The seller denied shipping me a damaged unit, so after pouring through the manual (in PDF format) and reading a few online forum posts of people having problems with the unit, i discovered that i could play all six voices in the unit by putting the unit in mode 2 cascade mode (the Matrix 1000 has a cool feature that allows you to link several units to multiply their polyphonic voice count.) However after playing the unit for a while i noticed there was also something wrong with the voices as well.

It is very simple to find out if the Matrix 1000 synth has a dead voice: Just play an arpeggio with 6 notes, holding each note, and listen to how many notes play. However it is very hard to find out if any voice chips have other problems, because most patches are setup to cycle through all six voice chips to handle polyphony.
So when you play a note in the Matrix 1000, the synth will usually start playing on any of the six chips, so playing the unit through a keyboard is not a proper way to test the keyboard, because you don’t always get the same results.

I found out a way to test the voice chips without having to open up the unit and physically swap the chips one by one. To do this, the following must be done:

1-Isolate the voice chips by using a synth patch that only uses only one oscillator.
2-Play all MIDI keys (i used 88 keys, C1 to A7) by using a MIDI file at velocity 120 to cycle through all six CEM3396 narrow-body voice chips and check their frequency and amplitude consistency.

To accomplish step 1, i used the free Editor Librarian JsynthLib to edit any one of the free library patches into what you see here:

To accomplish step 2, i used Ableton Live 8, connected the MIDI out of my DAW into the Matrix MIDI in and the synth audio output into my computer’s audio interface.
You don’t need to use Ableton, i am sure you can use any DAW.
I created a MIDI file with all 88 notes. Unfortunately I noticed for some strange reason that when i was playing back the MIDI data, the synth would play one note and skip the next, so i added an extra short dummy note between each long note, and the data played fine.

Here you can download the MIDI file i used and bring it into your Audio workstation:

  Test MIDI file with 176 notes. (1.6 KiB, 44 hits)

I recorded the outcome of the MIDI data playback back into Ableton and analyzed the Wave file in Sound Forge:

By looking at the wav file, the cycle through the six voices is very obvious. The chips do not have a consistent amplitude output, and one of the chips actually drops out completely but then it picks up the output at higher frequencies.
This means this unit not only needs at least two of its voice chips replaced, it probably has some more serious issues since the voice is not consistent across the keyboard.

To find out exactly what chip needs replacing do the following
1-Put the synth in Extended Function mode by pressing the Select key until the Ext Func. LED is lit.
Press 7 and press Enter.
Press the + key until you see 1 in the display and press Enter.
Now you have the synth in Voice Display mode, where the number of highest gated CEM3396 chip is displayed - counting from right to left on the circuit board.

2-Run the MIDI test again and listen for any audio dropouts and frequency shifts while watching the display. There you will be able to spot the location of the chip or chips that are having a problem.

Leave me any comments if you have any questions, and if you are an Oberhein Matrix 1000 owner, don’t forget to check my review of the different editors / librarians available for the synth HERE