uO_c 8hp ornament and crime.

[snowtires]

Anyone have extra pcbs for sale? I can't find one for the uO_c anywhere

Depending on what panel you want Synthcube might. Their website isn't that great for looking this up. For example they don't have board+panel but do have boards and panels separately for the same price as the combo.

https://synthcube.com/cart/index.php?ro ... ption=true

Awesome, thank you!

[Neutron7]

MiSW has them as well https://michigansynthworks.com/collecti ... _c-1-1-pcb

[Crunchyave]

Hey everyone,

I just finished building a uO_c, had a great time! The module powers up without issue, no burning smells, etc. However, I am having some problems with correct voltage output and calibration:

Output 1 is outputting a constant -10.7v, no matter what the calibration settings.
The other three outputs, I am getting significant voltage drift on the order of about 0.25v, and it won't settle in. Unlike output one however, I can calibrate them across the range, but they won't stay in place.

I reflowed the DAC and can't see anything amiss - I'm not sure where else to look though. Any help is appreciated!

[bawbag]

Did you deviate from the BOM at all?

[Bartimaeus]

for output 1, have you tried removing the resistor connecting it to the opamp, so you can test that pin in isolation as it were?

voltage fluctuation sounds like a problem with the power supply. have you measured whether the 5V, 3.3V, and reference voltages are all stable? you might want to double check that all of your caps are soldered right. those smd electrolytics always bug me, because it's too easy to miss when a pin isn't soldered right.

[Crunchyave]

Did you deviate from the BOM at all?

Not that I'm aware of - I had to make a couple part substitutions due to things being obsoleted or backordered, but I took care to match the values of the substitute parts. I may need to go back and doublecheck that though.

for output 1, have you tried removing the resistor connecting it to the opamp, so you can test that pin in isolation as it were?

voltage fluctuation sounds like a problem with the power supply. have you measured whether the 5V, 3.3V, and reference voltages are all stable? you might want to double check that all of your caps are soldered right. those smd electrolytics always bug me, because it's too easy to miss when a pin isn't soldered right.

I have not tried testing the resistor and I'm not sure what pin that would be - I've built a few through-hole kits prior to this but the uO_c is my first SMD project, so I'm still pretty much a noob at this.

I will check the electrolytic caps though, you're right that it was hard to see whether they were connected well or not. I did reflow all the op amps and some of the passives last night.

Lastly, I'm not actually sure where to test the 5v and 3.3v measurements on the board - what spots should those be accessed at?

[bawbag]

Did you deviate from the BOM at all?

Not that I'm aware of - I had to make a couple part substitutions due to things being obsoleted or backordered, but I took care to match the values of the substitute parts. I may need to go back and doublecheck that though.

for output 1, have you tried removing the resistor connecting it to the opamp, so you can test that pin in isolation as it were?

voltage fluctuation sounds like a problem with the power supply. have you measured whether the 5V, 3.3V, and reference voltages are all stable? you might want to double check that all of your caps are soldered right. those smd electrolytics always bug me, because it's too easy to miss when a pin isn't soldered right.

I have not tried testing the resistor and I'm not sure what pin that would be - I've built a few through-hole kits prior to this but the uO_c is my first SMD project, so I'm still pretty much a noob at this.

I will check the electrolytic caps though, you're right that it was hard to see whether they were connected well or not. I did reflow all the op amps and some of the passives last night.

Lastly, I'm not actually sure where to test the 5v and 3.3v measurements on the board - what spots should those be accessed at?

No worries - you've got it almost working, so we just need to push it over the finish line. However, as it's a first-ever SMD job, would you mind posting up some hi-res pictures of your build? Even a smartphone camera will suffice at the closest possible focal length. You might need three or four photos to cover the board, but that will help in diagnosing things.

[Bartimaeus]

unfortunately the schematic doesn't have component numbers, but a lot of stuff is still identifiable:

to check voltages, measure at the pins of the voltage regulators and make sure they match up to the voltages specified in the schematic.

[Crunchyave]

Awesome, thanks for the replies! I’ll post up some close pics later this afternoon.

[Altitude909]

unfortunately the schematic doesn't have component numbers, but a lot of stuff is still identifiable: ..

to check voltages, measure at the pins of the voltage regulators and make sure they match up to the voltages specified in the schematic.

Why not use the uOC schematic, that looks like OC

https://github.com/jakplugg/uO_c

[Crunchyave]

for output 1, have you tried removing the resistor connecting it to the opamp, so you can test that pin in isolation as it were?

voltage fluctuation sounds like a problem with the power supply. have you measured whether the 5V, 3.3V, and reference voltages are all stable? you might want to double check that all of your caps are soldered right. those smd electrolytics always bug me, because it's too easy to miss when a pin isn't soldered right.

Update:

I reflowed the electrolytic caps and that seems to have solved my voltage drift issue. There is still a small amount of drift, but rather than getting 0.25v swings it's more like 2-3 millivolts. A friend of mine that's built several of these says that's pretty normal to see, so I'm thinking this problem might be fixed!

I reflowed a few other things that looked suspect but output 1 is still outputting a consistent -10.7 volts. Work has been crazy so I haven't gotten decent pictures of the rest of the board, but will do that probably tonight.

[Crunchyave]

Alright, here's some (hopefully clear enough) pictures of my uO_c work. At this point the only issue I'm aware of is that output 1 voltage is a constant -10.7 volts. The other inputs calibrate properly and my voltage drift (which used to be around 0.25v) is now to down what I think is a reasonable 2-4mv.

There might be other problems with the input stages - I haven't calibrated them as of yet.

[Bartimaeus]

i don't see anything too off about the build. here's an idea: try de-soldering R1, then measure the voltage on either side of it. that's the resistor connecting the DAC to the output buffer, so it the -10.7V is on the DAC side you know it's a DAC issue, and if the -10.7V is on the opamp side you know it's something with the opamp. though i'd also just measure voltages on U3.1 to make sure it's getting the correct power and vbias voltages.

[Crunchyave]

Thanks, will check those things. I had to reflow the DAC several times to get it right so I hope I didn't fry it in the process, especially since it would be challenging to do that without lifting the traces and destroying the PCB.

[bawbag]

Thanks, will check those things. I had to reflow the DAC several times to get it right so I hope I didn't fry it in the process, especially since it would be challenging to do that without lifting the traces and destroying the PCB.

The joints below could do with some touching up. It also looks like you have a lot of flux residue that needs to be removed. It can also cause issues, so get your isopropyl alcohol out and give it a good wash.

[skinpop]

I'm currently building one of these. Is it possible to load the firmware before installing the teensy on the module by simply connecting a usb to the teensy and uploading the hex file?

[synthetek]

I'm currently building one of these. Is it possible to load the firmware before installing the teensy on the module by simply connecting a usb to the teensy and uploading the hex file?

Yes, as long as you haven't cut the power trace on the teensy

[skinpop]

I'm currently building one of these. Is it possible to load the firmware before installing the teensy on the module by simply connecting a usb to the teensy and uploading the hex file?

Yes, as long as you haven't cut the power trace on the teensy

Thanks! Also I forgot to ask, but is it correct that power can be connected either way(there is no "negative" marking)? It says "Either way" on the PCB...

[Altitude909]

..

Thanks! Also I forgot to ask, but is it correct that power can be connected either way(there is no "negative" marking)? It says "Either way" on the PCB...

no its a joke. it says that so you have a 50/50 chance of destroying the module.

[skinpop]

..

Thanks! Also I forgot to ask, but is it correct that power can be connected either way(there is no "negative" marking)? It says "Either way" on the PCB...

no its a joke. it says that so you have a 50/50 chance of destroying the module.

I managed to not burn down the house, and everything is working perfectly. Thanks

[emmaker]

..

Thanks! Also I forgot to ask, but is it correct that power can be connected either way(there is no "negative" marking)? It says "Either way" on the PCB...

no its a joke. it says that so you have a 50/50 chance of destroying the module.

Looking at the schematic I think you can put power in either way. This is not a O&C and it has a full wave rect. to deal with this. Someone else should check this out.

Jay S.

[autodafe]

I have a calibration issue with ALL uO&C I have built (4 of them , not my first uO&C).
They all have a fixed voltage of 1.15V at their outputs, when trying to calibrate the various -3V, -2V and so on.
No shorts on the DAC or on the OPAs, I checked v_bias (between R13 and R14 and C21) and I can measure 1.23V
I have +/- 1.15V constant voltage at each output jack, always, and all the pins of the two OPA2172 have +/- 1.20 on them (excecpt a +12 and -12 on pins 4 and 8)
Maybe a wrong component on them?
I attach a picture of one of my builds...

Any idea for this fixed voltage at each output?

[autodafe]

OK, I think I got it. Resistors around U3 and U4 (R3, R5, R9, R11) where not the correct values.
Swapping them with the CORRECT 100K ones solved the calibration issues. Next, check if all other 100K resistors are correct (probably not)... maybe I got a wrong bag or a wrongly labeled bag???.
that's why one should always measure resistor values with a MM before soldering :-)

[Altitude909]

..or use a brand that has labels on them

[bawbag]

Yup - I recommend the Koa Speer RK73H series. They're blue, clearly labelled and cheap.