MIDI-DAC not working

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Baldanders
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MIDI-DAC not working

Post by Baldanders » Sat Mar 14, 2020 8:30 am

Hi Tony and everybody else that could help. Thanks already for trying to!

My MDac Issue 4 doesn't come to live. It doesn't do anything at all as far as I can see. So I guess the PIC is shot? I put my voltmeter to the pins, and I see 5V on the VDD pin and the reference voltage pins and several others.

What should I try to do?
Regards,

Gabriel

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Synthbuilder
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Re: MIDI-DAC not working

Post by Synthbuilder » Sat Mar 14, 2020 5:29 pm

Unless the PIC has been zapped by a static electric discharge it's probably OK. The most common fault on problematic units is that the midi input socket being wired incorrectly. So the first thing to check is the midi through output. Try to ascertain whether valid midi data is being passed through to the midi through output socket. If it isn't then the fault lies somewhere in the wiring of the midi socket or the opto-coupler.

If midi data is getting to the through output, then it could indeed be the PIC, although other things can cause the midiDAC to malfunction.

Remember to try different midi channels too. Channel selection isn't very intuitive on the midiDAC so, in the first instance, it's usually easier to put all four little switches in one state and then see if the midiDAC is responding to midi channel 1 or 16.

Do you have a scope? If so check pins 4, 5 and 11 on the 4104, U15. These three digital lines should be a stream of +5V pulses. If one of them is stuck at 0V or +5V, check the soldering around the PIC and U15. If all three are stuck at 0V or +5V then the PIC could be dead.

Tony

Baldanders
Learning to Wiggle
Posts: 24
Joined: Wed Apr 29, 2015 12:07 pm

Re: MIDI-DAC not working

Post by Baldanders » Wed Mar 18, 2020 10:31 am

Hi Tony,

thanks a lot for your suggestions, I got the module to produce gates and some kind of CV voltage and light the legato LED, but there is still something amiss, U5 (CD4066B analogue switch) gets really hot, and I think it's now toast, and there are no more gates etc. I checked the component values surrounding it, and they all seem to be correct.
Sorry for troubling you with such stupid stuff.

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Synthbuilder
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Re: MIDI-DAC not working

Post by Synthbuilder » Wed Mar 18, 2020 2:31 pm

Any component getting hot is a bad sign. It's not necessarily the wrong components being installed but solder shorts. It'll be worth checking the underside of the board for any excessive solder on the pads around U5. That said, R16 being much too low, say 100R instead of 100K, would cause the 4066 to overheat.

The midiDAC will work without U5 - although you'll not have any glide available. So just remove it and see what happens. Check that pin 1 of U4 goes up and down with the note value - it should go up by slightly less than 1V per octave, with 0V being the lowest note and +10V being the highest note.

Tony

Baldanders
Learning to Wiggle
Posts: 24
Joined: Wed Apr 29, 2015 12:07 pm

Re: MIDI-DAC not working

Post by Baldanders » Fri Jul 24, 2020 1:26 pm

I got the module to work perfectly fine after shelving it for a month or two. Replaced U5 and reflowed some solder points again, and it worked! Trimming it was a breeze, the bus out goes directly to my ASV. The slide is excellent!

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Re: MIDI-DAC not working

Post by Synthbuilder » Sun Jul 26, 2020 6:13 am

Baldanders wrote:
Fri Jul 24, 2020 1:26 pm
Replaced U5 and reflowed some solder points again, and it worked!
Thanks for letting us know. I'm glad you got it sorted. :tu:

Tony

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