x0x troubleshooting - audio out?

x0x troubleshooting - audio out?

Postby far gon » Sat Jan 10, 2015 2:06 am

Hi,

I recently completed the x0x-heart build with the euro Pacemaker PCB and grayscale panel. Well at least almost completed...

I am beginning to tune the module but ran into issues and I am posting here for clarification and possible troubleshooting advice.

I trimmed J4 pin 1 to 5.33v. (as per the first step in tuning in xox-heart manual)

Moving to the next step though, I am not getting audio out from J6 pin 1 or 3. Rather I seem to be getting a constant voltage to ground according to the oscilloscope.

J6 Pin 1 = 9.2v to ground
J6 Pin 3 = 6.08v to ground

I am getting 5.2v from the 7805 regulator (from supplied mouser cart), and that is what is found on pin 11 of the euro header on the x0x-heart.

The filter and envelope seem to be functioning properly, as when I plug an external oscillator into the ext in, the filter will sweep the audio. Sending gate to the gate jack produces enveloping as expexted. Env Mod and Decay work as expected and the CV jacks work with CV applied. This was all tested after connecting the heart to pacemaker via headers.

Any tips, ideas, or insight would be greatly appreciated!

Thanks!
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Re: x0x troubleshooting - audio out?

Postby guest » Sat Jan 10, 2015 11:29 am

did you apply a VCO CV when you tested? it sounds like the VCO is not making any sound (or else you would hear it from the filiter out). the VCO needs a CV to make sound, and one of the waveforms needs to be selected via the waveform switch (to hear it at VCF out). if that doesnt work, check J5 for the same CV as you are applying.
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Re: x0x troubleshooting - audio out?

Postby far gon » Sat Jan 10, 2015 12:57 pm

I just tested these recommendations.

I applied CV to the 1v/oct in jack at various static voltages from a sequencer as well as from a DC offset. Switch set to either saw or square produces no tone at the filter out. I can measure the voltage applied to 1v/oct at J5 pin 2, and they match. Measuring J6 pin 1 or 3 produces now 10.6v and 5.8v respectively (slightly different from readings last night) with front panel knob movement producing no change on these readings.

With gate applied to Gate in jack, still no sound from either filter out or VCA out. When an external oscillator is plugged in to Ext in, I can get audio from filter out, and VCA out with gate applied. This is all tested with the x0x heart attached to Pacemaker and front panel.

One thought of maybe where I could have potentially messed up the x0x heart is: when probing for J6 pin 1, I accidentally clipped the probe onto one of J3's jumper wires. Not sure if this would have any effect, but I thought I would bring it up anyway. I read another thread about 'digital-in sensitivity' and thought maybe my probing could have affected this section.

THANKS FOR YOU HELP!

p.s. I also have two other x0x-hearts to build up, so if i cant get this one working, I will build the others to help troubleshoot. I was hoping to be missing something obvious and/or to avoid making mistakes in the next two
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Re: x0x troubleshooting - audio out?

Postby guest » Sat Jan 10, 2015 2:50 pm

it definitely sounds like something is not right. do you feel comfortable probing around the SMT stuff? it would be great to see the voltages on U11 and C33. another thing to try, is to connect up headphones or you scope, so you can monitor the VCO output, and then apply pressure to the components in the VCO area (while it is powered up and running - with CV). its possible there is a bad solder joint on one of the SMT components, and that it is making intermittent contact (all of the PCBs are tested before shipment, but if its intermittent, it could have passed QA and then failed later). it wont hurt anything to touch the board while on.

its possible that Q28 could get damaged if pin1/2 are shorted on J6, or if pin1 is shorted to ground by some other means.

the voltages you are reporting are usually a fault of Q17/18 not resetting properly. double check that that area of the board is clean and looks ok. is anything getting warm?
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Re: x0x troubleshooting - audio out?

Postby far gon » Sat Jan 10, 2015 3:40 pm

I measured these points you suggested.

On the LM35, U11:

Pin 1 = 656mV
Pin 2 = 576mV
Pin 3 = 32mV
Pin 4 = 0.00uV
Pin 5 = 5.2V
Pin 6 = 5.2V
Pin 7 = 4.8V
Pin 8 = 12V

C33 = 9.2V

I will do some pushing on components in the VCO section to see if there is something intermittent as well.

Now that you mention the possible damage possible to Q28... I do now have a sinking feeling that I potentially shorted Pin 1 to ground (middle pin) of J6 when first trying to probe for the audio out. I should have taken a break as it was late at night and had been soldering all day, so im not sure if that happened. I thought I saw a waveform on the scope when first probing J6 pin 1, but it was brief as I hadn't clipped the probe on and also I wasn't sure if the 'waveform' i saw for a split second was just the contact and de-contact of the probe. It was not a bi-polar wave if so. In the attempt of getting a good clip connection, there is a chance the probe made contact to both pin 1 and 2. Maybe its a harsh lesson to learn what we all have heard at least once: take a break, come back to it even the next day to test. I was excited for the acid, and it was an easy build, so my confidence was high ...but a bit unfounded.

If it is damaged Q28, is there any way to make sure? And if so, what would the replacement part or part # be? Looks like three pins to rework if that needs replacing, which ive never done on this small, but I would try it to save the x0x!
Last edited by far gon on Sat Jan 10, 2015 3:43 pm, edited 1 time in total.
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Re: x0x troubleshooting - audio out?

Postby far gon » Sat Jan 10, 2015 3:42 pm

And the Q17 part of the board looks clean as far as i can tell. Nothing seems to be getting warm anywhere.
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Re: x0x troubleshooting - audio out?

Postby guest » Sat Jan 10, 2015 3:56 pm

the voltages seem ok on U11 (im assuming no CV was applied). the way to test Q28, is to scope C33 with your scope, and see if there is a waveform there (apply a CV first - at least 2V). if there is a waveform there, and not at J6, then Q28 is bad. its a tricky rework, but it is replaceable.
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Re: x0x troubleshooting - audio out?

Postby far gon » Sat Jan 10, 2015 4:21 pm

Correct there were no CVs applied with those measurements.

So I have applied 3.2V to 1V/oct in. Measured same voltage at J5 pin 2. (jumpered tune header)

But at C33 I still get a constant 9.2V, no waveform.

I really appreciate your help in this matter!
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Re: x0x troubleshooting - audio out?

Postby guest » Sat Jan 10, 2015 4:35 pm

ok, so its probably not Q28 (it still could be, but a different failure mode). get your multimeter, and measure the voltage across R104. this will be bit difficult, since it is so small, so if you need to, put one probe on C34 and other other on R104 (one side of C34 connects to one side R104). check the voltage drop for 0V CV, and 5V CV (or voltages somewhere around there). this will check to see if the expo converter is working. the voltage should double (it will be something small, a 100mV or something).
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Re: x0x troubleshooting - audio out?

Postby far gon » Sat Jan 10, 2015 4:49 pm

At 0V CV applied, voltage across R104 = 123 mV
With 5v applied, voltage across R104 = 159.6 mV
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