Yet Another MIDI issue, I know, but this one is weird

Discontinued products Anushri
#1

Here is the issue:

I have an Arturia Keystep. Using CV and Gate outputs, the synth works as it should.
Under MIDI, there is nothing. I am using CH1, but tried several different channels. The learning apparently worked, but it took several minutes for the LED to start blinking again (timeout?).

  1. Here is what works: MIDI is read by the MCU, because I can read it on the MIDI out. Exactly what key I am hitting, note on, etc is reflected immediately on the output MIDI port. [So MIDI channel is working to MCU]

  2. The voltage on the DAC (IC20, pin 8) does not change. It stays at 0.579V when I push any key

  3. IC20, pin 1= 4.982V, pin 2 = 4.191V, pin 3 = 0.040V, pin 4 = 4.925, pin 5 = 0V, pin 6 = 1.806V, pin 7 = 0V and pin 8 = 0.579

  4. All power checks out, on all points in the troubleshooting sheets

  5. There is continuity from IC23-15 to IC20-2, and from IC23-13 to IC19-2

I double checked resistors, etc… I am at a loss. Both the DAC_Pitch signal and external VCO_CV_IN are supposed to go to IC6 on pin 2 (after a couple resistors). Again continuity is good.

Here is another thing, under auto tuning, there are two tones, a low and a high. The voltage for the high tone (At VCO test point or IC20-8) is at 0.579V and drops to 0.156 V for the low tone. Tells me the DACs are likely working.

The tuning cycle never stops, just plays two tones, each for about 6 seconds. I can change the pitch by turning the Cutoff up or down.

Anything to point to would be appreciated.

#2

You could swap IC20 and IC19. They are both the same DACs.
But before I would check all other components connected to the DAC output (R60, R57, C30). The DAC_PITCH signal is also going to IC2A (Opamp for VCO_CV_OUT), take it out for testing. Measure also the 4.096 REF voltages.
Check also continuity from the ATmega to the other DAC inputs: SCK (pin3) and MOSI (pin4)

#3

Switched DACS, same result
Pulled U2, Voltages at socket pins are:
pin 1 = 4.010
-2 = 4.050
-3 = 0.001
-4 = -4.949
-5 = Cycles from, 0.403 volts up to 1.130 volts then back down again to
-6 = 4.050
-7 = 4.010
-8= 4.975
continuity on MOSI, SCK, SS1_DAC, SS2_DAC all caps and resistors checked

All 4.096 and -4.096 voltages are measured at sources.
IC1 = 4.090
IC12 = 4.093
IC13 = -4.095

IC6B pin6, has 0.236 Volts while 4.094 volts exists at the other end of R56.
R74 has -4.094V on pin 3, and -3.723 off the wiper and pin 1. There is -0.007v at pin 7 of IC6B
IC6B, pin5 has 0.000V
IC7, pin-1 has 2.371V

I no longer have MIDI coming from the MCU. But I can see it on the scope. I can see the voltage drop when I release a key (on both ends of MIDI). Disconnect the MIDI in, and even pull the OK1 opto-isolator… I have a constant Note OFF on CH1 coming out the MIDI port every second. A clock?

Changed 6N137s, no diff
Changed MCUs, no diff

Dont know if this matters, but on IC22, pin-9 I have a constant 0.315V. If I push any of the momentary buttons, it drops to 0.278. I would have thought that to be a greater difference between high and low. There is a 244.5 Htz signal on the pin. Pushing buttons does change between synth, Keybd, and drum, etc.

This is an Anookum board, but did not know if there was that much of a difference.

Still looking to see what is wrong. I am not sure it is just MIDI that is not working.

#4

There is something wrong, should be also 4.094V on IC6B pin6.
Take IC6 out and measure the DAC_PITCH voltage again, when playing different notes. Best to measure with the scope.

But it is working with CV IN? Strange.

#5

I read your first post again: the strange behaviour could also be the MCU running at a too low frequency. Did you program it yourself. Did you set the right fuses?

#6

I read the make file and only noticed the lock settings, lock:0x2f,

so no fuses are set. Are they set the same way as the Ambika or Shruthi?

efuse :0xfd, hfuse:0xd2, lfuse:0xff

I use the Atmel Studio and ICE to program the boot loader and then the 0.92 ver hex file

#7

You can find the fuse settigs here:
https://github.com/pichenettes/anushri/blob/master/anu/makefile

#8

WooHoo!
Awesome, that was it.

Man, you learn something new everyday, Even if, there was no issue with components… i was still well worth going through this schematic, just to figure out how it is supposed to work.

I never would have figure the fuses, but if I remember now (yes, I should have remembered before), one of the fuses sets the internal clock to the external crystal.

Thank you Sir!!

#9

Glad I could help!
Though you distracted me first with all your DAC measurements, that I diregarded the other symptoms.