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.