Saturday, November 21, 2009

Fuseboard and volume slider

On the way to work I stopped by ELFA and picked up the fuse holders and some 500mA fuses. The fuse board is now changed to allow the mains power to go to the 230V wire on the transformer through a 500mA fuse instead. I also found an obvious fault in the synthesizer.

Here's a shot of the fuse board after I altered it.

After altering the fuse board and attaching it again I measured the voltage on the connector and it showed 230V coming from one of the pins. Nice.
After that I disconnected the output wires from the voltage regulator board and connected the mains power from the fuse board to it.
All the voltages seems to be present. I attached the connectors and measured the voltages on some random places in the Matrix 6 and got good voltages so I think the power supply is working properly.

Still, the display didn't light and none of the LEDs lit up. I don't know really which LEDs should light but I'm sure the display should give me some life signs. I didn't measure the 41V AC voltage for the VFD display so maybe that's a problem but I suspect there's something else wrong that keeps it from starting up. Also, I didn't look at the 5 and 12 volt supplies with a scope to check for ripples so I probably should do that as well.

When I looked closer at the boards I noticed the little board that holds the volume control slider. It looked like this:

Looks like somebody already did a repair here but it looks a bit nasty...

I magnified the nice part with the yellow wire. Check out the pads on the board. I doubt the volume control would work at all so I took it out and measured on it to check if the slider itself was ok. And, guess what. It's a stereo slider and one channel was completely disconnected and the other seemed to be broken about halfway on the track.
Now, this is a dual 50k ohm slider with 30mm travel distance. I tried to locate a replacement on the net and I found approximately nothing...
I guess I could probably use a similar slider if I find one, say with 10k or 100k instead, but I didn't find any stereo versions with 30mm travel length either...

So, I am going to try to put a rotary 50k stereo potentiometer in its place.
I am not really keen on drilling a hole in the front plate to fit the potentiometer but until I can figure out why the thing won't start up properly I guess I can just pull the wires for the put through the slider hole and leave the pot on the outside. I don't know yet, but I could at least find a regular pot, and it was cheap, so...
I ordered a couple of those and I'll try to come up with a clever and not too destructive way of using it instead of the slider.
Anyway, the slider is now removed and the board has been wiped a bit cleaner using isopropanol.


  1. Hi Peter , your blog is a godsend for me so m really glad I found it!

    I want to convert my 110v matrix 6 rack to 240v is all that you did just move the fuse to the other position ?
    No moving wires or retiring at all ?
    Thank you !


    1. Sorry that should have said "no rewiring at all ?"

    2. Hi,
      As far as I remember that's all I did (wow, already 3 years ago?).
      Though I can't guarantee the 6R has the same power supply so I can't guarantee that the same procedure will work, but it is likely :)

      Now that I look at this post, I start wondering what those varistors are rated for...
      Perhaps they should be changed as well?
      Anyway, it does start after just moving the fuse holder as it connects a different winding on the transformer. I have had the M6 do some weird things, which I can read in later posts.

      But again, it would be best to take a look at the service manual/schematics to check if the power supply is indeed the same in both machines.

      If you feel condident working with high voltage stuff, I guess you know the necessary precautions. If not, please don't try to do this on your own. Double check the connections with a multimeter before you plug it in if unsure.
      Good luck and feel free to ask again if there is anything else you're wondering about.


  2. Hi Peter ,
    Thanks for the fast reply!
    Time flies huh ;0)
    I removed the fuse board from my M6 and it looks exactly the same as your photo and so does the transformer (same model number), so I think that's all pretty encouraging.
    The only copy of the service manual I can find is mostly hand written and its scanned in quite low resolution so can't quite make out some of the labelling do you have a good quality copy at all ?
    Yeah I'm comfortable with working with voltages I'm trained in electrical safety and have a bit of electronics experience so hopefully I won't blow it or me up ;0)
    Thanks very much for your help I really appreciate it !

    1. Well whadya know, It worked !!!
      I literally removed the old fuse bought some new pcb mount holder pins soldered them in, dropped a 500mA fuse in, plugged it in and she fired up ( no smoke - because we all know we don't want the smoke to escape ha ha).
      It's working great ( except the right side audio output which I'm sure is a different issue entirely, the headphone out works in stereo fine fine so I'm quite happy to investigate that one further).
      Played through some presets and it sounds lovely !
      I found a better more legible copy of the service manual too.
      I just want to say a huge thank you for blogging about your experience in the first place!

      Cheers !


  3. I also found what the problem was with the right output - There was no problem, The Matrix 6 only outputs in mono !
    The right output is for use in split mode where the lower registers come from the left out and the upper registers from the right, or the other way round so its not actually a stereo unit!