strange tuning problem, can't find in forum...
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strange tuning problem, can't find in forum...

by Jinx on Sun Jul 22, 2012 7:49 pm

First of all: when in keyboard mode (normal pitch) and playing C to C, every note coming out is wrong. the first 8 keys are all playing the same tune, except from Low C wich is playing C0. from about G to hi C the tune changes but the problem is there over every octave. And when i pitch down to what is supposed to be the lowest octave, it actually pitches up.
When in normal pitched mode, the low C on the keyboard is playing C0 (supposed to be C1?).
the problem is still there in pattern mode.

i'm getting 5.333 from the power supply so the problem has to be somewhere in the VCO section. It's obviously getting the wrong voltages, but why and how to correct it?

:?:
Jinx
 
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Re: strange tuning problem, can't find in forum...

by MMM on Mon Jul 23, 2012 3:51 pm

Could be a problem with IC9.

Are you sure the switch in the normal octave happens at G and not at A?
MMM
 
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Re: strange tuning problem, can't find in forum...

by Jinx on Mon Jul 23, 2012 5:21 pm

Hey!
Yes, you're right, Switch happens at A.
in normal octave, when I play C to C this is what comes out: C = C0, from C# to G# = C1? (same tune), A = the switch happens here.
A# = is same tune as A,
B and C = 1 note higher.
its messed up in the other octaves as well.

So it's probably IC9...? I rechecked all transistors and solderjoints etc...
Could it be the microcontroller?

should i simply go get another 74HC174?

Thank you very much for helping me out
Jinx
 
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Joined: Wed Jul 18, 2012 8:05 pm

Re: strange tuning problem, can't find in forum...

by MMM on Wed Jul 25, 2012 12:48 pm

So, if the switch happens at A it means that the highest bit for the note number becomes active and in turn adds to the control voltage. Which leads to the conclusion that a number of the lower bits don't work (most notably the three lowest minimum) since the don't add to the control voltage.

There are about three (or four) places where things can go wrong, going backwards from the summing point of the CV:

1. The resistor network (R74 to R90) (or its connections to IC9).
2. IC9
3. The connections between the processor and IC9.
4. The processor itself.

To determine where the fault lies you need a multimeter.
First we measure the incoming data line to IC9. We use pin3 here. Press the "A" key. You should see 0v here. Then press the A# key; and pin3 should switch to 5v. Press the B key and it should go back to 0v, press the C key next to it and should again jump to 5v.

If this works it means that probably the processor and its connections are ok. If this works try the same procedure as above with pin2. Here you should get 5.33v however.

Get back to us and let us know what you found out.
MMM
 
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Re: strange tuning problem, can't find in forum...

by Jinx on Sat Aug 04, 2012 10:47 am

Finally had time to do some troubleshooting...

So, From A to C i'm getting 0 and 5v, as you said. But pin 2 does NOT show 5.33. however pin 1 does...
Jinx
 
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Re: strange tuning problem, can't find in forum...

by MMM on Sun Aug 05, 2012 11:41 am

pin 1 is the 5.33v supply so this will naturally show this voltage.

If pin 2 doesn't change at all it hints at IC9 being defective.
MMM
 
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Re: strange tuning problem, can't find in forum...

by Jinx on Mon Aug 06, 2012 9:14 am

yes, I will change IC9 then.

thank u very much :)
Jinx
 
Posts: 9
Joined: Wed Jul 18, 2012 8:05 pm