Xpantastic!

Hi all, and thanks for all the input regarding the Matrix-12 repair  
that I am doing.
The unit is in very good shape and sounds good. Among other things all  
the displays are fine, panel is good, wooden sides are in fine shape,  
and all keys (except one broken) looks good.
There are some trouble manuvering the synth, as several buttons don´t  
respond. It was kind of dirty before I started working on it, so I  
guess several of the buttons needs to be cleaned, as I had to do with  
they keys (both keytops and key contacts).

I have run across some various interesting failures:
- One voice is dead, and I have pinpointed this to the fact that the  
VCA output (leg no. 14) of the CEM3372 is dead. All else on the chips  
works as it should; inputs, VCF sections and all. It is just the VCA  
that is gone. Usually when a CEM chip fails it is completely dead, so  
this was a puzzle for me. Swapping chips with other voices turns it  
into a working voice. So a new chip is needed here, then.
- The rotary encoders all work, thankfully. It is just the Schmidt  
trigger chips that seems to mailfunction, just as Karl Schmeer  
suggested (thanks!). If I rotate the encoder with a very specific  
speed - slowly, but not too slowly - I can make it increase somewhat,  
but it is difficult. Reducing with the same encoder is no problem.  
Need new chips probably, or maybe just clean up?

Then the real problems:
- Only voices 1-6 can be heard. Internally all voices (both 1-6 and  
7-12) seems to work fine (I can scope it all). This might be connected  
to the next problem...
- The "Voices 1-6 / Voices 7-12" button is unresponsive, so I have no  
way to see if the second voice board is turned off or not. Are there  
any workaround for this?
- Unresponsive buttons. How do you usually solve this? Clean them, or  
change them? It seems to me that there are standard momentary buttons  
underneath the large black front panel buttons.

The power supply have a fairly high physical hum, so at one point it  
probably needs to be changed. The internal power is stable, but a  
little bit off spec, like +12.1 and -11.82. Is this to much off? I  
hope not, because that means I have to rebuild the whole power, with  
new regulator transistors and all.

Terje Winther
terje.winther@...
http://www.wintherstormer.no/