Wouter wrote on 2023-03-10, 02:41:

I had this same problem on a Pentium MMX 233 with an Aztech 2320 based card. I checked the MIDI IN pin with an oscilloscope, and it had full amplitude high frequency noise on it. My hypothesis was that the level converter on the WP32 could not handle the high capacitance on the MIDI IN line of the sound card, so I added an AC terminator (series capacitor and resistor) between MIDI IN and GND. Now it works perfectly.

I'm having a similar problem with an Aztech 2316 based card. It would be appreciated if you could provide a little more detail regarding the AC terminator modification. What value capacitor and resistor did you use? Did you solder these to the sound card at the back of the wavetable header, or on the McCake itself?

Can anyone let me know what is the expected behaviour of the various LED parts on the rear of the McCake board?

I believe I have an issue with getting enough power to my board, as I get no output at all - but only the first two green LED's are lit; I believe these are '5v' and '3.3v DAC' ... the others all remain unlit ('3.3v Pi', etc).

I don't currently have the FDD power supply in place (lack of free FDD connectors from my Pico PSU supply) - would this be typical behaviour in that situation?

you need to connect the FDD power else the pi will not get power
the wavetable header alone is not made to power a pi4 - even if it's a CM4 running at low freq

That explains it then 😀

Snoozer wrote on 2024-03-17, 12:01:

Wouter wrote on 2023-03-10, 02:41:

I had this same problem on a Pentium MMX 233 with an Aztech 2320 based card. I checked the MIDI IN pin with an oscilloscope, and it had full amplitude high frequency noise on it. My hypothesis was that the level converter on the WP32 could not handle the high capacitance on the MIDI IN line of the sound card, so I added an AC terminator (series capacitor and resistor) between MIDI IN and GND. Now it works perfectly.

I'm having a similar problem with an Aztech 2316 based card. It would be appreciated if you could provide a little more detail regarding the AC terminator modification. What value capacitor and resistor did you use? Did you solder these to the sound card at the back of the wavetable header, or on the McCake itself?

I used a 100 ohm resistor and a 10nF ceramic capacitor, soldered on the McCake itself between MIDI in (bottom row, second pin from the right) and any ground (top row):

MIDI IN --- 100R --- 10nF --- GND.

I assume these values may have to change depending on the board, and in general I found it quite finicky, so would not consider this anything else than a bodge. It works for me though.