XOX(BOX) Trouble shooting

XOX(BOX) Trouble shooting

Postby spotta » Thu Apr 23, 2015 1:46 pm

Hi Guest

You kindly mentioned in a pm to me that I should post here with regards to my X0XB0X (not heart) issues due to the official forum being a bit quiet these days.
It was built from Willzyx PCBs with the rare parts kit and the rest was self sourced. It was built with the X0Xio back panel (not the full kit) originally but since having issues this has been totally removed to make it a stock X0X for troubleshooting.

When it's powered up and turned to keyboard mode, all I get is clicks http://www.spotta.net/downloads/x0x/x0x-keyboard.mp3
In Random I get clicks and the odd note http://www.spotta.net/downloads/x0x/x0x-random.mp3
I have swapped the BA6110 for another but that made no difference at all.
I was advised to check the VCF voltages and what I’ve found so far is a recurring theme of voltages being a bit lower than they should be –
C17. The positive side should be 8v but is 6.6v
R62. The ‘wire’ end is 6.5v not 8v, the ‘body’ end is 6.7v not 8.1v
R99. Wire end 4.8 not 5.3v – cannot get to the body end without removing the PCB
R63. Wire end 2.4 not 2.7v – cannot get to the body end without removing the PCB
Q10 end nearest to R71. 3.25 not 3.75v
I’ve had it up and running for two hours this afternoon and still nothing got hot.
Due to the fact that I have used flat top LEDs, I've tried to avoid removing the board from the panel as I fear I wont get all the LEDs back in and will have to remove and resolder them, but I managed to do it today and grabbed some pictures of the other side of the board and cannot see any shorts. http://www.spotta.net/downloads/x0x/x0x-LED_SIDE.zip
I've also tried the 'click-be-gone' mod but it made no difference to the click.
The other thing I have read that could be contributing to the clicks is that I have used non specified LEDs and their corresponding resistors.
These are the LEDs I used http://www.rapidonline.com/Electronic-C ... -LED-29333
I lined one of each colour up and choose the resistors to achieve consistent brightness across all the colours, I ended up using
Red : 330r
Orange : 330r
Yellow : 100r
Green : 100r

My next step is to continue checking voltages and that I have fitted the correct resistor values all over the board, but as the best X0X Guru I know, if any of these issues ring any bells or if you can suggest anything else that might be worth checking first, I would greatly appreciate your input.
spotta
 
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Re: XOX(BOX) Trouble shooting

Postby guest » Thu Apr 23, 2015 3:48 pm

does it still make note sounds every so often in random mode? if so, the problem is probably not in the analog section. it can clearly make sounds, so its just not being told to make sound. does turning accent/slides on or off change anything? the clicks are the VCA trying to make sound, so the VCA most likely works, but an audio signal is not getting to the VCA. can you listen at the resonance pot and waveform switch and tell me if you hear any sounds there?
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Re: XOX(BOX) Trouble shooting

Postby guest » Thu Apr 23, 2015 5:03 pm

another thing to try, is to put the x0x in keyboard mode, and play every note, from one octave down, to 2 octaves up. make sure that they are all dead.
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Re: XOX(BOX) Trouble shooting

Postby spotta » Fri Apr 24, 2015 6:54 am

Good advice that!
Here's what I get from the top ocatve manually playing from C to C - http://www.spotta.net/downloads/x0x/x0x-top-octave.mp3
Also I seem to have a fair bit of DC offset, Image - http://www.spotta.net/downloads/x0x/x0x-top-octave.png
but as I haven't done any tuning or tweaking yet, I'll only worry about that if you think I need to.

As for probing the switch and res pot, I've seen they way they recommend in the x0x manual using a cheap ear-bud - is it also advisable to do this with a modified lead going into my desk, which or without the cap at the end?
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Re: XOX(BOX) Trouble shooting

Postby guest » Fri Apr 24, 2015 11:19 am

excellent, that was what i was expecting. so whats happening is that your DAC for CV generation is busted. the x0x doesnt produce any sound for CV less than 1V or so. its most likely a bad IC9. set the x0x to keyboard mode, and play a note in the middle of the range. then, measure the voltages on all of the pins of IC9 and IC11 and report those back. basically, i want to see if the latch is passing the voltages through appropriately. IC11 is the buffer amp, and that might be bad, but less likley.
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Re: XOX(BOX) Trouble shooting

Postby spotta » Sat Apr 25, 2015 3:50 am

IC9
1-5.33
2-0
3-0.01
4-5.05
5-5.33
6-5.05
7-5.33
8-0
9-0.01
10-0
11-0.01
12-5.33
13-5.05
14-5.05
15-5.33
16-5.33

IC11
1-4.65
2-5.33
3-5.33
4-0
5-2.57
6-2.59
7-2.59
8-11.98

Actually hitting the keyboard didn't seem to make a difference, these voltages were seen before I pressed it, during, and after.
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Re: XOX(BOX) Trouble shooting

Postby guest » Sat Apr 25, 2015 11:50 am

well, the problem is not with the DAC, but rather with the VCO (assuming it did not make any sound when you pressed that note in keyboard mode - correct?). but, just a quick verificiation, is to put your multimeter on the CV out, and just play the note up the scale on the keyboard, and make sure the CV increases each time. it is probably fine, though.

can you take another measurement:
put the x0x in keyboard mode, play a note in the middle of the range (you dont need to hold the note).
measure CV out and all the voltage on Q26

im guessing there is either an issue with the CV scaling (R106,R100,TM5,R118) or there is a leakage current in the reset circuit (Q24,Q25,Q27). a couple of quick things to try: 1. clean any flux off the board near the VCO. 2. turn the TUNE pot all the way up and see if any more notes appear at the higher range.
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Re: XOX(BOX) Trouble shooting

Postby spotta » Sat Apr 25, 2015 12:43 pm

Yep, CV out increases as notes are played as you described

playing G the CV out is 2.59 and Q26 voltages are from back of board to front
5.05,
fluctuating between 7.58 & 8.14, but sort of a regular LFO type of fluctuation.
4.78,
5.34
5.34

Turning the tune pot all the up helps a bit.
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Re: XOX(BOX) Trouble shooting

Postby guest » Sat Apr 25, 2015 1:24 pm

so the scaling seems good, is there any flux on the board?

measure the voltage across R105, and monitor it for 30s or so, and see if it moves at all.

double check that Q24,25,27,28 are all orientated correctly and are the correct parts.
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Re: XOX(BOX) Trouble shooting

Postby spotta » Sat Apr 25, 2015 2:35 pm

There is flux on the board, meant to be no clean, but its there.
R105 steady 8.41v the leg end, 0v the other
all four transistors confirmed.
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