Howdy! Recently I purchased a broken MKS-20 in the hopes of fixing it. When I bought it the description said “powers on but doesn’t output sound” which was accurate. The description also went on to explain how all of the plastic spacers for the effects board were snapped and someone attempted to remedy this with glue.
Once I got it, I opened it up to figure out where to start. I found some new plastic spacers on Amazon that ended up being the perfect fit, so I installed them. In my initial test, there was absolutely no output whatsoever, however the screen (including the backlight!) and menus work as they should. I went ahead and rebuilt the volume slider and bypassed the relay since the relay is a know issue on these. After doing all that, there’s still no instruments. However if I adjust the volume slider up and press a key on my MiDI controller, I hear what sounds like faint white noise in the background (thru the headphones and other outputs) which lasts for a second or two after the key is no longer pressed and then stops.
So here’s a recap of what I’ve done so far:
Replaced the spacers for the effects board
Disassembled, cleaned, and rebuilt the volume slider
Removed and bypassed the relay
Checked all the fuses with a multimeter
Re-seated all the connectors
Checked the battery (I think it was replaced because it’s measuring 3.3v)
Inspected the boards for cracks or breaks (they look perfect to me)
Any and all help would be appreciated! Thanks!
Check pin 11 on the CPU A board with an oscilloscope if you can, that will be the audio from there. If you have audio then the fault could be with the effect board.
MKS 20 Roland SERVICE MANUAL | SynthXL - Service & Repair Manual This link will get you the service manual.
Thanks for the reply! I have an oscilloscope but I don’t currently have probes for it. With alligator clips and RCA cables, would it be possible to use them to connect the pre-effects board audio signal to an amplifier to hear it through speakers? I do have the service manual and I’ve been looking at it scratching my head for days now lol. Once again, thanks for the help!
I’m not sure, I’d not try it either, last time I tried something similar I turned my audio interface into a paperweight with 15v.
I had another look at the diagrams as something was bugging me, I should have said cpu board B. board a is responsible for midi, latches (buttons) and display. CPU board B takes the data from IC11 on pins 17-25 to the DAC where it is then turned into audio and comes out at point 11. I am thinking that either a cable is loose between the CPU B and the effects board or worst case scenario its a dead DAC.
I have only seen one case where a DAC went down and thats on a JP8000 I am still waiting on parts for 
I’m about 99% positive it isn’t any of the cables. I’ve reseated them all about a dozen times at this point. One thing I am curious about is whilst I was looking at CPU board B, I noticed what I can only guess are various test points on the board. The ones I’m referring to in particular are the ones labeled AUDIO OUT, D/A OUT, and AG. Would any of those carry the pre-effects board audio signal for me to connect an oscilloscope to?
EDIT: Also, do you have any idea what IC10 does? I noticed it gets quite hot (compared to the rest of the ICs) when the unit is on and I’m not sure whether or not this is normal behavior for that particular IC.
Yes indeed, those test points are what you need AG being audio ground D/A OUT being post DAC and pre effects.
IC 10 on board B should be a ROM (MB7138H) they are usually pretty warm.
Alrighty, good to know that there shouldn’t be any concern about that IC. Going to order some new probes for my scope and check those test points. Once I’ve tested them, I’ll come back here with the results.
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