How do I check the i2s board?

[rhester72]

(Note: I didn't read the part about the bridges potentially being wrong until after I built my board, because...because.)

Is there any way to check to see why my i2s is completely mute short of desoldering the entire i2s adapter board to look at the bridges? The LCD works, MIDI IN works and I get pwm output.

[gmcn42]

Hi @rhester72!

(Note: I didn't read the part about the bridges potentially being wrong until after I built my board, because...because.)

Well, I only just added the info yesterday as I was not aware of the potential problem up to now. My own boards all came with the bridges soldered as in the picture and I carelessly assumed that would be the general case. 🤷‍♂️

Is there any way to check to see why my i2s is completely mute short of desoldering the entire i2s adapter board to look at the bridges? The LCD works, MIDI IN works and I get pwm output.

Yes, but you will need a multimeter to measure resistance.

1. Disconnect the power supply.
2. Set the multimeter to a reasonable value, like "100kΩ" or on that order.
3. Identify the places between which to measure: the board pin marked GND is "L" and pin 20 of the DAC chip (see picture) is "H". Pins marked 1-4 are the configuration pins,
   
4. Measure if a configuration pin has either
   a. no connection to both "H" and "L"
   b. low-resistance (<1kΩ) connection to one of them
   c. high-resistance (>1kΩ) connection to one of them

The correct configuration would be 1-L, 2-L, 3-H, 4-L. If that is already the case, something else is wrong.

If you measure a case of no connection (4a) or wrong high-resistance connection (4c), that's easily fixable by connecting the pin in question to either the unmarked pin between "4" and "G" (if it should be "H") or GND (if it should be "L"). Just solder a small piece of wire on the bottom of clumsyMIDI.

If you measure an opposite low-resistance connection (4b), for example 1-H, then unfortunately there is no recourse but to desolder the DAC, sorry :/. Please don't try connecting anything as this would result in a short circuit and probably fry your board. Your best bet in this case is using desoldering wick and a strong soldering iron.

The most likely culprits for a DAC with no audio output are pins 3 (Mute) and 4 (I2S format). Wrongly set 1 (filter type) and 2 (de-emphasis) would -- I believe -- result in a somewhat distorted output.

Good luck and let me know how it works out!

[rhester72]

All four are low, which means I'm muted. Desoldering. :)

[gmcn42]

Ah. that's unfortunate :/. So for clarification there were about 0 Ohms to GND on pin 3? That would seem like a pretty huge error by the manufacturer because - well - the DAC board won't ever produce any sound like that.

[rhester72]

I figured nobody would believe me unless I actually put this photo up (and MAN, was getting it off the board a royal PITA!)

I'm not hooking this all back up until I solder the bridges and breadboard it :P

Yes, by all means, please warn builders not to make ANY assumptions about bridges of any kind.

Thank you kindly for your help and guidance and this amazing project! Even with just PWM output, it was clear this is something very special - and even an old-timer like me can do it! :)

[gmcn42]

Well, I can imagine it wasn't easy but that is a nice desoldering job if I've ever seen one! :)

I'm not hooking this all back up until I solder the bridges and breadboard it :P

You should be fine once the bridges are soldered up right. But testing on a breadboard can't hurt, of course. For that you'd only need the vertical row of pins (right side in your pic). The horizontal ones are all unconnected on the clumsyMIDI PCB but they help with mechanical stability (see schematic).

please warn builders not to make ANY assumptions about bridges of any kind

Yep, good idea, I'll update the README with a more visible warning.

Thank you kindly for your help and guidance and this amazing project!

You're very welcome! Have fun with it!

[rhester72]

Just providing a brief status update - I was delayed due to running short (read: completely out) on breakaway pin headers, which was resolved yesterday - got the i2s properly configured with the solder pads (and finally learned how to distinguish resistance to 0 versus NC on my new multimeter! :P) and confirmed all connections back to the Pi header, but no joy...I think the i2s gave up the ghost during the desolder, but no pragmatic means to know for sure.

In any event, new i2s on the way tomorrow, but decided on a ground-up rebuild for neatness...I overordered on parts for exactly this reason. =)

[rhester72]

Rebuilt with a new i2s and all good - it sounds AMAZING! Thank you!