[sdiy] CASIO MG-500 MIDI guitar synth almost repaired but...

[Pete Hartman]

Yes it probably will.  It's not common in newer equipment, but older
stuff has it.  This made me somewhat crazy with my first MIDI project;
my only MIDI controller was a Yamaha PortaStudio keyboard which used
this, and I was entirely unprepared for the flood of FE bytes. :)

Most MIDI receivers either ignore it, or use it as intended (the idea
was if the stream of active sensing stopped for longer than X time,
turn all notes off, to deal with unplugs/cable breaks).

MIDI-OX will let you filter out incoming active sensing bytes, if I
remember correctly, so you can focus on checking the rest of the MIDI
stream.

Sounds to me like it's all working and you're done :)

Thanks

Pete


On Fri, May 30, 2014 at 8:59 AM, Jean-Pierre Desrochers
<jpdesroc at oricom.ca> wrote:
> Ok.
> So it seams the MG-500 will always generate that message ?
> I can't see any way to stop that message from being sent
> using the 9 DIP witches settings..
>
>
> Le 2014-05-30 09:49, Pete Hartman a écrit :
>
>> Active sensing is totally normal, expected and yes, there are tons of
>> them.  Set MIDI-OX to ignore them, most keyboards will do the same.
>>
>> On Fri, May 30, 2014 at 8:44 AM, Jean-Pierre Desrochers
>> <jpdesroc at oricom.ca> wrote:
>>>
>>> I'm working on a CASIO MG-500 guitar synth that needs repair.
>>> User's manual here:
>>> http://www.arcenson.com/public/Casio_MG-500_MG-510_user_man.pdf
>>>
>>> and a very badly scanned service manual here:
>>>
>>> http://www.arcenson.com/public/Casio_MG-500_MG-510_service_man_and_parts_list.pdf
>>>
>>> At first there was no MIDI out and the 'tune' leds didn't lite.
>>> So I checked on the net for any clues about this guitar
>>> and its 'common' failures..
>>> I found out that most of the SMT electrolytic caps on its boards
>>> were prone to get bad and spill bad electrolyte on the PCB surrounding
>>> traces
>>> and eventually corrod them until they get cut open.
>>> So I did a replacement on all of them and YES they mostly
>>> were bad with corroded pads. OK.
>>> Now I got MIDI back out and the inner tuner is working well. Fine.
>>>
>>> Now here is the remaining bug..
>>>
>>> The first time I plugged the guitar MIDI out to my
>>> PC MIDI port (using MIDI-OX MIDI command viewer)
>>> to check the MID generated commands I noticed
>>> an incoming MIDI signal called 'Status:FE ....Event: Active Sensing'
>>> that keep looping all the time out of the guitar MIDI output..(!!!)
>>>
>>> When I played each strings I could see MIDI signal
>>> responding to my pick strucks 'through' the annoying 'FE - Active
>>> Sensing'
>>> messages
>>> that still keeps going and going..
>>> See the MIDI-OX log snapshot here:
>>> http://www.arcenson.com/public/MG-500_MIDI_log.JPG
>>>
>>> First I thought there was some kind of noise coming
>>> from the HEX pickup that would be amplified by the analog stages
>>> and keep triggering such message.
>>> There are 6 gain tuning pots at the back of the guitar
>>> that need to be set for good strings sensitivity for each of them.
>>> I tried tweeking each of them but the Active Sensing message kept going
>>> and filling all MIDI-OX log lines.
>>> In the schematic there are 6 tests points to verify the analog
>>> amplification/filtering outputs for each string.
>>> They showed a nice filtered waveform when each string are played.
>>> Right next to these tests points there are comparator opamps
>>> for envelope and Peak detection that I didn't check yet
>>> but I don't think they are causing this MIDI message always showing.
>>> Maybe they are ..
>>>
>>> Please note that when strings are plucked there MIDI messages show
>>> 'inserted' through the Active Sensing invading messages
>>> so I think I can tell the CPU and digital stuff work and read
>>> clearly the 6 analog signals..
>>>
>>> I'm stuck at this point so far..
>>>
>>> Any help welcomed.
>>>
>>> J-Pierre
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