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9700 MIDI2CV8 acting strangely - note scale wrong
http://www.paia.com/talk/viewtopic.php?f=8&t=438
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Author:  Etamin [ Sun Jul 01, 2012 7:23 pm ]
Post subject:  9700 MIDI2CV8 acting strangely - note scale wrong

Hi Scott

I powered up the 9700s today and found that the note intervals are 'messed up'. It has worked since build in mid 2010, and I have made no mods, or changes.

If I play a C, then C#, I get a semitone interval, but then D sounds a C again.

Arbitrarily calling C 1, C# 2, D 3, etc to B 12 I get the following:

In Out
1 1
2 2
3 1
4 2
5 5
6 6
7 5
8 6
9 9
10 10
11 9
12 10

This pattern repeats each octave, and clearly there is some logic to the wrong notes, but I cannot work it out.

Do you have any idea what is happening?

Thanks, Peter

Author:  Etamin [ Mon Jul 02, 2012 1:30 pm ]
Post subject:  Re: 9700 MIDI2CV8 acting strangely - note scale wrong

I gave this some further thought, and starting with C=0 instead of 1, then converting the numbers to binary, any 'bit 2' is being ignored.

In Out
0 0
1 1
2 0
3 1
4 4
5 5
6 4
7 5
8 8
9 9
10 8
11 9

So maybe bit 2 of DAC output is misbehaving?

Peter

Author:  PAiA-Scott [ Thu Jul 05, 2012 2:53 pm ]
Post subject:  Re: 9700 MIDI2CV8 acting strangely - note scale wrong

It might be the second lowest bit not making it into the CV. Listening to the ramping during the output test phase of the Self-test mode might reveal if it's trouble particular to the mode. The line into IC8-pin 11, DAC1 should toggle with the ramping and a dc voltage reading would not be fixed, but an average of the hi/lo states.

Maybe the IC2 firmware just needs to be removed and re-inserted in it's socket to correct contact between a pin and the socket.

Maybe a joint to IC7 or IC8 was borderline and time has moved it to the not making condition.

IC7 links the D/A converter with the micro-controller and if a part has failed, it would be the more likely one than the D/A.

Author:  Etamin [ Thu Jul 05, 2012 5:47 pm ]
Post subject:  Re: 9700 MIDI2CV8 acting strangely - note scale wrong

Hi Scott

Thanks for the suggestions. I tried reseating the firmware chip first as the easiest option after a quick visual inspection of my quality soldering job, but still no go.

So I reflowed all the solder joints on IC7 and IC8 and it is working again. Clearly my soldering job was not quite the quality I thought :oops:

All is well again, thank you so much for helping me to get it working again - it really is a great module, with way more features than any other MIDI to CV in the price range.

Peter

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