Resistor Issues

[JSteady]

Hello,

I'm in the process of troubleshooting my VCF on my xoxbox.

I was checking all of the resistors and noticed that about 5 of my 10k resistors are reading from 6.4k-7.4k The rest are fine. Would these lower readings cause any problems with my VCF portion? It currently has no output but the VCO is send a saw and square signal to the east end of R64

Thanks

[guest]

if youre measuring the resistance in circuit
then its very common for a resistor to read lower
as youre measuring all the other resistors its connecte to

the best way to debug the vcf
is to compare voltages with the voltage map post

[JSteady]

T tested the entire VCF section and most of the voltages were +/- 0.2v

I started to work further back into the VCO section of the board and found a dead section involving Q27, D25, Q25 and Q24 I tried swapping out all of the transistors with new ones and the voltages are still reading zero.

Here is a picture of the section and the voltages around the area


http://i124.photobucket.com/albums/p22/ ... 5440PM.jpg

The RED circles are areas indicating 0 voltage

Im boggled

[guest]

measure the resistance to ground
at those points

although if the vco is working
then its not likely that there is anything wrong

do you have an oscilloscope by any chance

listen for signal
on either side of c14

[JSteady]

I don't have access to a 00scope but I did try to look for a signal using a sound scope. Here's what I have on C14

The sign-wave is almost identical on both sides of C14.

v

[JSteady]

when I probe q1,q2,q4 and q3 with a voltmeter, I get audio in my headphones. :/ I'm not sure what that means

[guest]

how much of the x0x is built

that waveform looks ok
you should try turning the resonance pot and cutoff
and see what the signal looks like

[JSteady]

The unit is complete for the most part. The cutoff and resonance are working properly. The only issues are the lack of output on the headphone jack, the decay and accent knobs do nothing and the unit holds the not on when the pattern is not being played

[guest]

my apologies
i assumed it was the vcf that wasnt outputting

is there sound from the mix out
can you hear sound on the volume pot

can you check the gate out jack
and see if it goes to 12v when a note is pressed
and back down to 0v when a note is released
and check what the voltage is when its holding a note as you say

[JSteady]

gate out is giving my 0vdc and I'm not getting anything on the volume knob.

[JSteady]

also, I am getting no sound out of the headphone or mix out jacks unless I have the voltmeter touching the pins in the transistors.

[guest]

ok
the gate is busted
put the x0x in keyboard mode
and measure the voltage on all the pins of q37
for both a note being played and not being played

[JSteady]

from left to right on q37

off- 0
on- 0

off- 11.58
on- 11.58

off- 3.9mV
on- 1.57

[guest]

it looks like q37 is bad
or its base is not soldered in well

try rehitting the joints
and if that doesnt work
replace q37

any npn transistor will work
as its not in the audio path

[JSteady]

YEAH!!!!! Changed it and it works

Thank you so much!!!!

I am very thankful for people like you on the internet!

I owe you a beer