16n Faderbank: build help, dev suggestions

[okyeron]

To clarify: These are usbmidi values?

Have you tried testing the voltage out from each jack in the back? (I use a mono cable with alligator clips to connect to my voltmeter).

Last Q - what resistor values did you use?

[Rodrigo]

Yeah, sorry, usbmidi.

I changed the default MIDI channel to 15 in config.h, but otherwise I uploaded the code as is.

I haven’t tried checking the voltage out of the jacks (yet). I’ll try that.

I used the resistor values in the build guide, so 5.6k and 10k resistors alongside the opamps.

[okyeron]

And 1K at the top? (R1 - R16)

EDIT - Pictures could be helpful if you’re excited about that.

[Rodrigo]

Yeah, 1k along the top.

Took some measurements. All the faders from (circa) 0V to 2V on the faders that go from 0-95, and from (circa) 1.2V to 2V on the ones that go from 59-95.

Looks like the top (1k) ones say 1001. The 5.6k ones say 5601 and the 10k say 1002(?).

[okyeron]

Maybe input voltages are not right for some reason? (which would mean something wonky with the teensy maybe or a short somewhere?)

Check at the teensy and for each IC (or cap)

[Rodrigo]

I’ll check the teensy pins, and will double check the diodes tomorrow (man, the “lines” on those diodes are reaaaally subtle!)

[Rodrigo]

So I’m getting 1.7V on the teensy 3.3V pin, so I’m guessing that’s the source of (one of the) problem(s). I’ll double check my soldering on the teensy, but in looking at the pins, everything looks fine there.

Could that indicate some funny business on the diodes themselves? I had to really really squint to see the lines on them, so I think I’ve wired them in in the correct orientation, but I can’t be certain.

[okyeron]

I think if the diodes were backwards, you’d just have them blocking voltage to the i2c jack instead of passing it.

Post a pic of the diode section? If you angle the board back and forth sometimes that makes it easier to see the lines on the diodes.

I’d suspect a short on C1, the top right pin of the Mux or around the diodes.

You can check for shorts with your multimeter in continuity mode - with the teensy not plugged in.

Also - you might clean up the flux everywhere with some isopropyl alcohol.

Outside possibility the teensy is messed up. :-\

[Rodrigo]

Ok, cleaned everything with ethyl alcohol (for the life of me, I couldn’t find isopropyl in any of the local DIY/hardware stores), and reflowed the Teensy and areas that showed up problematically.

Still getting only 2V on the Teensy 3.3V pins (as well as the 5V and VUSB pins). There’s no bridges anywhere on the Teensy or the first stretch of the components after the 3.3V.

Also reflowed some of the resistors on the channels that don’t go down all the way and one is better. I should have ordered lots of extras for the tiny components, I didn’t really think that far ahead. I’d love to just pop off the resistors on those opamp channels and solder on new ones.

Is there anywhere else I can measure to see if some voltage is getting divided somewhere it shouldn’t? It just seems weird that there isn’t >2V anywhere in the system (even on the raw VUSB).

[Nordseele]

@Rodrigo could you share some high res (daylight if possible) photos of the full board please (one of each side) ? I sold you this board, sorry I didn’t see the thread earlier I’d like to help as well . I’m pretty sure there’s nothing wrong with the board itself but it’s better if we can get a overview of the whole board

[Rodrigo]

I’ll do some photos tomorrow (maybe a scanner will probably work the best). Thanks!

[Nordseele]

Yeah let’s do that, I hope we can fix the issue

[Rodrigo]

Scanner pics came out all blurry, so I took some with my phone. Hopefully they are clear enough.

(my roll of solder is near the end and its got a lot of white dust near the core, and that has somewhat reacted with the ethyl alcohol cleaning, so there’s white crusty looking stuff everywhere. I’ve reflowed things a couple times so the connections are good, even though they largely look gross and dusty)

[Nordseele]

Yes, I know this reaction with the flux, I’m posting a link for IPA at the end of this message.
It’s a bit hard to detect a cold joint now but since you said you already reflowed everything and there aren’t many components maybe it’s not the issue.

Did you use a magnifying glass (at daylight) ?

First thing I see, I think all your diodes are reversed. If the lines of D1 D2 D3 D4 point up, that’s not correct. But is it the cause of the issue ? I need to take a look at the schematic, I can’t see anything else on this side right now

Also, you should reflow the pins of the faders on the back, I’m not sure they’re all correctly connected to the GND

I buy the IPA directly from Hoefer, 1-3 days free delivery. It’s a bit problematic now that the faders are soldered on but generally I dip the board in IPA and I use an anti-static brush. Then I remove the IPA with paper towels and let the board and components dry for a few minutes.

[Rodrigo]

Yes, I know this reaction with the flux, I’m posting a link for IPA at the end of this message.

Glad I’m not going crazy.
I’ve had this (gigantic) roll of solder for years that has been fine, but I’d never seen this kind of weird reaction before. When I have defluxed in the past I used some defluxing solution I got (this was for some mic mod stuff I did a bunch of years ago), so hadn’t encountered this crustiness.

I dip the board in IPA and I use an anti-static brush.

Super smart! Nearly all my DIY stuff is through-hole, and generally a bit more…rustic, so these kinds of tips and tricks are new to me.

Will IPA get rid of the ethyl+flux dustiness or has that ship sailed for this board?

First thing I see, I think all your diodes are reversed.

Gah, those diodes!

I got so caught up in trying to even see the lines that when I did, I guess I lined them up the wrong way. I’ll see if I can pop them off and get them back on in the correct orientation. I guess this only really impacts the i2c stuff?

Also, you should reflow the pins of the faders on the back, I’m not sure they’re all correctly connected to the GND

I’ll hit all of those on the back again. I specifically reflowed/refed those yesterday since they look weird, but I guess it’s just a thirsty connection point.

I’ll reflow some of the problem areas and try flipping the diodes around and see if that helps.

Thanks for the detailed help!

[Nordseele]

Will IPA get rid of the ethyl+flux dustiness or has that ship sailed for this board?

Yes, it’ll remove the white things, is that corrosion ? I don’t know how to call this effect Anyway, fill a recipient with 2 cm of IPA, and brush the board with the anti-static brush, now that the hardware components are in place it will be a bit difficult to see if everything is dry, that’s the problem

I guess this only really impacts the i2c stuff?

I’m not sure, they’re connected to the 3.3V line

I’ll hit all of those on the back again.

You should put more solder on the pins of these faders, I think they’re crucial in the circuit, if their ground is not connected humm… That could be the cause of the issue. I encountered something like this in one build, I forgot to solder a pin of one fader.

[okyeron]

Fwiw - I use 91% rubbing alcohol from the drug-store/pharmacy. This is isopropyl alcohol (IPA).

I also use an toothbrush dipped in IPA to scrub areas of a pcb - esp around jacks if the flux buildup is heavier there. Then wipe with a microfiber cloth or paper towel.

The dry toothbrush can also be good if there’s lint or little fibers left after wiping with a towel.

[Rodrigo]

The IPA stuff (or rubbing alcohol in general) seems to be way less common over here.

I did manage to find a big bottle at a huge garden/DIY store thankfully. Holy moly this stuff is magic! Almost too good, as after scrubbing the shit out of the board there’s a bit of gummy residue kind of “all over”. I’ve gone over it a few times and it’s looking pretty clean.

With the crust left from the ethyl gone, there’s definitely some joints that could use more flooding. I’ve ordered some new solder too as I don’t trust the inner part of my roll at the moment. And I’ve ordered another set (and then some) of the resistors/caps/diodes in case any of mine cooked too.

Will report back once I get everything and give it another go.

[bpcmusic]

Good luck!! My fingers are crossed for you.

[okyeron]

And I’ve ordered another set (and then some) of the resistors/caps/diodes in case any of mine cooked too.

Highly unlikely that you’ve cooked any of those components enough to kill them. But handy to have spares just in case.