carlibration problem / note out of tune

[975262801]

so it seems like it is the VCO circuit problem.... what should I check next?

[975262801]

For working unit, the dc reading of pin 7 of IC 11 is :
C d e F g a b c
2.01 2.17 2.33 2.43 2.59 2.75 2.91 3

For the non -working unit, just when I try to test it, it goes back to normal again, so I am not able to check the voltage when it is at the "out of tune status". However, I have check the voltage when it is with the correct tune.
2 2.16 2.33 2.41 2.57 2.77 2.94 3.02

Not much difference with the working unit when it is working. I have no idea why it goes out of tune sometimes.......

[guest]

the normal sequence should be
2.000
2.083
2.166
2.250
2.333
2.416
2.500
2.583
2.666
2.750
2.833
2.916
3.000

are you using the same sequence of notes
to compare the out of tune to the intune on the broken x0x
as the resistors have a bit of mismatch to them
and you can see a big jump of voltage at 2.43v on your readings
everything before that is pretty close
and then after that they are all +20mv high
which is one fourth the way to the next note

take those same readings the next time it goes out of tune
also put your finger on all the parts in the vco and dac
and see if wiggling or warming them up with your finger
makes the x0x go out of tune
probably play a sequence of low c to high c back and forth
and listen for drift

[975262801]

Thanks for the reply.
viewtopic.php?f=12&t=12453
Just wondering if the reference voltage in this link 100% correct? Some people said this is not 100% correct. I just want to know if the VCO section reference voltage is correct in there so I can test every parts in the VCO section. Thanks

[guest]

i never looked too closely at that section before
and it seems like a lot of voltages are off

[975262801]

This is the DC voltage of the VCO section. Can you take a look at see if there is anything looks wrong in there? Thanks

[guest]

those all look good
except for a slight offset voltage in ic11
which shouldnt make too much difference
as long as its consistent

does the problem change any
when slides are on or off

[975262801]

Do you mean Slide on and off in keyboard mode? I will try that tonight. I have build a new x0xb0x and I have double check all resistors/caps/ transistor again and again. I am sure they are correct, but I have the same problem again. I can not get an exact ONE OCTAVE range from key 1 to key 8. I turn the TM5 to the Max already. I can tune it from C to B only which is a very narrow range. If the DC voltage is all fine in the VCO area. What other parts can affect the octave range?

[guest]

if you shift an octave up or down
can you get a full double frequency

turn off the power
and measure the following resistors
tm5 r106 r100

[975262801]

I think I have the same problem in this link. Narrow range and high octave.
viewtopic.php?f=12&t=25652
100A 100B is 500 ohms, R106 is 24K , TM5 is 1.7k (it is a 5k trimpot)
Today, the x0xb0x has the note drifted and out of tune like crazy. I record a new DC voltage reading. I have written them in light blue text. It is only one of the reading. Sometimes the reading is different on those blue text area.
I have already re-touch all soldering point with the soldering pen to make sure they have a good contact, but it doesn't fix anything. I think must be one of the component has problem.

[975262801]

I have measure pin 7 of IC11, the reading for each octave first note/key is 1V 2V 3V 4V

[guest]

is the votlages on r90 as you have shown
5.33v on one side and .16v on the other side

what note were you playing for that test

it looks like a short in ic12 perhaps

[975262801]

I am still having this problem. I have build a couple of x0xb0x and they all has this small octave range problem. Even I turn the TM5 clockwise to the max. I can only get C to B from Key one to Key eight. I can't get one octave at all. I have solder everything so carefully and I am sure all the resistor/ Caps value is right. I solder all IC correctly. However, I am still having this problem........so...... I think the only way to solve this problem is to use some other new parts from new supplier. Do you know which components or transistor or IC will cause this small octave range or high pitch problem? I think I will just change all the related parts......

[975262801]

1583 ? 733P ? 536F ? 2SK30AY ? AN6582 ? Themistor ? what should I change?

[975262801]

One of my friend told me that it could be the gain effects the frequency in the VCO . I am so confused.
1./ Is the problem 100% comes from the VCO section ? What about the I/O board? I got 5.33v and 11.89v on J4.
2./ The VCO section is so small. There is not many R's and Caps / IC and transistor in there. May be I should change some new parts from new supplier to see if that solve the problem. Which component should I change?