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poorly MKS70 - not sure what's up with it, MIDI fault?

Posted: Mon Jun 15, 2020 12:18 am
by squatski
So I know I probably won't get a reply soon because forums are so quiet now but it's worth a shot

OK SO! I managed to win an mks70 off ebay. There was a picture of it on showing the version so I though, yeah this should ok.
Had it for a week and it sounds a bit 'circuit bent' without actually being circuit bent. So the firmware turned out to be the notorious old as h**l version 1.0 or.. I can't remember
anyway I bought the v.06 / v.06 / v.08 chips. so that's v.08 for the main board and 2 x v.06 for the JXP8 boards (as I call them hah!)

DIDN'T fix the issue. I'll have to do an audio demo, sometimes you can press 6 keys on your MIDI keyboard and the 6th one will have this circuit bend noise. It's quite a cool noise that I've already sampled but I'd rather have a working mks70 seeing as I paid a c**p ton of money for it.
Would could the problem be.
I even sysex'd over the original bank presets to it and it still sounded messed up... the classic electric piano sound of patch A:1, you have like dips in sound level on some notes, and there a really harsh noise.

When I got the mks70, one of the previous owners had actually left a load of expletive message on the patches which at first I thought was pretty amusing (I won't repeat them here) but I can't help feeling they were put on there out of frustration this mks is damaged beyond repair which worries me!

ohwell, at least I got a pg800 for a ripoff price haha :roll:

I'll post up some sound example soon, it MAY just be that something is setup wrong.....y'know with the whole dual mode/xfade/this that and the other........

Re: poorly MKS70 - not sure what's up with it, MIDI fault?

Posted: Tue Jun 16, 2020 10:50 am
by Mesmerised
Does not sound like a setup error to me. Possibly a broken voice on one of the boards. Can you tell if the erroneous sound comes from one of the boards (upper OR lower, or both)?
I would try to isolate the voice - maybe there's a test mode? (get the service manual...)
Good luck!

Re: poorly MKS70 - not sure what's up with it, MIDI fault?

Posted: Tue Jun 16, 2020 1:11 pm
by squatski


test on saw wave, newest firmware 1.08 but was the same on the old eproms.

ALWAYS:
10 normal notes ( - )
1 dead note ( x )
1 weird ringmoddy sounding note (r)

sometimes different variation across the keyboard like
- - - x r - - - - - - -
- - - - - - - x r - - -
- x r - - - - - - - - -

you get the picture, the 2 odd ones are always together.

Re: poorly MKS70 - not sure what's up with it, MIDI fault?

Posted: Tue Jun 16, 2020 1:23 pm
by squatski
ok turns out they're not always together, on this example it's:

- x - r - -
on a 6 note sequence.

also there's a h**l a lot of mains 50hz hum coming out the mks mix out, not so bad on the A / B outs


Re: poorly MKS70 - not sure what's up with it, MIDI fault?

Posted: Tue Jun 16, 2020 1:28 pm
by squatski
and for something extra freaky...

it's in the background quite faint I had to turn it up a lot.

Re: poorly MKS70 - not sure what's up with it, MIDI fault?

Posted: Sat Jun 20, 2020 10:37 am
by Mesmerised
Seems like you have two broken voices (2 out of 12). In 12 voice poly mode the assigner plays them in rotary fashion, that's why the patterns/keys are like that.
There is a test mode where you can find out, which voices on which board these are.
It's in the service manual. (Hold "write" during power up for test mode 1)
I can't attach the manual here but you should be able to find it online.

You might need a repair shop, looks like an issue not easy to fix.

Re: poorly MKS70 - not sure what's up with it, MIDI fault?

Posted: Tue Jul 14, 2020 8:50 pm
by squatski
My genius dad found the fault in the end and fixed it!

want to know what it was? one chip! one chip that needed replacing on board B.

a 1 of 6 chip which was:

BU40516
409 307
no idea what it does but it's a little 16 leg jobby. It pretty much cured the dead/weird note in an instance!
Many bits of schematics had to be examined it was a learning curve for both of us! well, I say 'us' I haven't a clue what was going on, wish I did! I only know how to drive it.

He will now be rewarded. I'll probably buy him something nice that I know he likes to drink! 8-)

Re: poorly MKS70 - not sure what's up with it, MIDI fault?

Posted: Wed Jul 15, 2020 9:33 am
by Yekuku
You should be proud of your Dad, thanks for letting us know :)
Obviously, the problematic chip was a 4051 analog switch that was routing signals from the CPU to the voices circuit.