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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.

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.

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.

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.

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.

clean the flux off if you havent already. if that doesnt do it, one of those transistors is bad.

if you want to be sure of which parts are bad before having to buy new ones/replace them, you can do the following test:

1. remove q25
2. put your multimeter in current mode, and measure the current between the collector and emitter pcb holes where q25 was. this will be the holes that go to q27 and q26.
3. play the lowest C, and then one octave up, and then another octave up, and so on until youve gone through the full range. the current should read around 3uA, 6uA, 12uA, 24uA, 48uA. the actual values might be different, but the thing to look for is a doubling of current with every octave.
4. if your meter doesnt measure current down to the uA range, then you can put a 100k resistor in these holes and measure the voltage across it (put one lead on each side of the resistor), and the voltage across it should double. but, a low quality meter might have trouble with this as well.

if the current doubles as described, then the problem is with q24,25, or 27. if it does not, then remove q28 and repeat the test. if it still does not double, then q26 might be faulty.

Update

I removed Q25 and tried option 3 but my multimeter was not registering anything. then a pack of 2SC536F & 2SA733P arrived from James so I replaced Q24, Q25 & Q27, I double checked again to clean the Flux from all components around the VCO, but no difference at all. I've ordered a new 2SK30AO so I can replace Q28 next.
I'm now going to remove Q25 again and try the resistor trick.

Removed Q28, same results. shall I order a new 2SC1583?

also, set your multimeter to the mV range for the current measuring tests. what multimeter do you have?

ok, set it to the 200mV range when doing the 100k resistor measurement.

were those with the capacitor removed? if so, then its sounding like the 2sc1583 is the problem. what were the voltages on it for 2 different CVs?

so i went back and looked at some of the earlier debugging info you posted, and realized that i made a mistake. there is something wrong with the scaling. this could be Q26, or the resistors (most likely Q26). can you use your multimeter to double check the resistance of R100, R106, and R118 (make sure power is off). they wont read exactly right, as they are in-circuit, but they should be somewhat close.

it looks like r106 might be bad. desolder one leg, and measure the resistance again out of the circuit. it should be 27k. it could be reading low becuase its in the circuit, or it could be bad. do the same for R118 (that should read 100k).

yes, use the 24k.

and my most sincere apologies for not catching this earlier. i feel really bad about having you rip apart half of the VCO, and order new parts and all. im not sure why i messed up my calculations the first time.

yes, reassemble everything, and it should work fine now.

awesome, glad to hear its working. and no need to send me anything, im just happy to help out.

Next question (you knew there'd be more didn't you!) started tuning tonight
With the voltage set to 5.33 I get 1.99 and 2.98 going to R90. in order to get the required 2v & 3v I have to adjust the voltage to 5.37.
I'm going to tune it set to 5.33 for now, I can always adjust. but knowing that I probably will use the CV out for other Osc's what would you recommend?

Also while setting up the low C, High C pattern to generate these voltages I've noticed that the sequencer step LEDs do not match up with the note LEDs, its like the step LEDs are almost a step behind the notes.
hopefully this will help show what I mean https://youtu.be/SimWJGfVuj4
Any ideas?

it's running sokkOS 1.9.1