Open Music Labs Forums

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!

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

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!

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.

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).

Those last readings of R104 were with my multimeter (which is somewhat inexepensive, and i'm unsure of its accuracy at mV levels). So in cross referencing with the oscilliscope (rigol ds1052e) I get different readings:

5v applied = 60mV ish (fluctuating a little)
0v applied = ~123mv again fluctuating.

When measuring with the oscilliscope, these measurements were fluctating as it seems to be a biased waveform of pretty high fequency. Is this correct?

Sorry if my measurements with the multimeter threw you off... I think its time for a proper meter.

the scope readings are even stranger. i would trust the multimeter more at low voltage levels, as digital scopes are pretty noisey below 50mV or so. it should be a DC level, though.

Point taken on the scope! Makes sense about the noise.

R106 = 5.06V, 4.99V
R118 = 5.08V, 0V
R100 = 5.11V, 5.08V
D25 = 467mV, 4.4mV (third pin is 0V as you mentioned)

put C33 on the scope, and watch the scope as you measure the voltage at D25 with you meter. if C33 stays at 9.3V, and D25 is still reading 400mV (or anything less than 5V for that matter), then Q28 is probably bad.

what that means, is that Q17 is off, and therefore its Q28 that is leaking the current into C33, which is not good. the C33/D25 measurement test i posted earlier would confirm this, as its possible that the act of measuring D25 shuts off Q17.

Well suppose i should have looked in the most obvious of places, the x0x wiki, to find the parts list pdf for the x0x-heart. I not completely helpless lol!

So I found the replacement part for Q28:

http://www.mouser.com/ProductDetail/ON- ... jFNw%3D%3D

and will tack it on to my next mouser order.

Is there anything else you can think of to get 'just in case' to replace (or test further)?

Thanks for taking the time to help me. In the great spirit of DIY, I will do the same for another in need if I can help. Just keep me away from probing your x0xen ;P

oh, another method for getting SMT parts up is to use solder wick and get as much solder up as possible, then lift the part off.

its probably worth taking Q28 off first before placing the order, to see if it is really the problem. let me know how it goes.

measure the resistance to ground from the various pins on j6 to make sure there isnt a short on the pacemeker, and if it all seems good, then put a new x0x-heart on.

wow, awesome news! and congrats on getting that sucker off, that was the difficult part. putting a new one back on will be much easier. which method did you use to remove it?