24 input daughter board better pics

[kurtus420]

So I managed to install the daughter board for testing purposes and I am having an issue. It it send midi signals through the head input on aux 9, if I hook a piezo up to it it starts to hum a tiny bit but it is audible. I have checked for shorts and don't see any, I have also tried replacing the mux with no success, still showing full midi output on the vu meter, midi light stays on for the aux 9 head input, all other channels are working. I'm not sure what would cause this, any ideas? Could it be the atmega644? Thanks

[dmitri]

So I managed to install the daughter board for testing purposes and I am having an issue. It it send midi signals through the head input on aux 9, if I hook a piezo up to it it starts to hum a tiny bit but it is audible. I have checked for shorts and don't see any, I have also tried replacing the mux with no success, still showing full midi output on the vu meter, midi light stays on for the aux 9 head input, all other channels are working. I'm not sure what would cause this, any ideas? Could it be the atmega644? Thanks

1. Check for shorts to +5 on the aux9 input.
2. Measure voltage on the aux9 input.

[kurtus420]

Voltage is .55 from vcc+ to pin 15 of sn74hc4851n all other pins are around 2-3v, I measured it from ground to pin 15 and get 4.5v?

So I managed to install the daughter board for testing purposes and I am having an issue. It it send midi signals through the head input on aux 9, if I hook a piezo up to it it starts to hum a tiny bit but it is audible. I have checked for shorts and don't see any, I have also tried replacing the mux with no success, still showing full midi output on the vu meter, midi light stays on for the aux 9 head input, all other channels are working. I'm not sure what would cause this, any ideas? Could it be the atmega644? Thanks

1. Check for shorts to +5 on the aux9 input.
2. Measure voltage on the aux9 input.

[dmitri]

If not advised otherwise, voltage is always measured against ground.
Looks like you have +5 on the aux9 input. Take the mux out of the socket. Do you still have +5 on the aux9 input?

[kurtus420]

Oops!! I am at work for 1 hour then I will pull the mux and report back here, thanks.

[kurtus420]

I'm getting 4.2v on pin 15 to ground with mux pulled, 0 volts on all other inputs

[dmitri]

I'm getting 2.2v on pin 15 to ground with mux pulled, 0 volts on all other inputs

And obviously it should be 0v when the IC is out and nothing is connected. Look for a cause of Vcc leakage to this pin - bad soldering, excessive flux and etc.

[kurtus420]

Thanks dmitri for your time, I have managed to get it working, (I think, actual testing to follow) it was another classic case of the flux leaking voltage but untraceable by continuity tests. I scraped around all of the connections leading to pin 15 on the mux and low and behold I have a working daughter board.

[Ken Forgettable]

Thanks dmitri for your time, I have managed to get it working, (I think, actual testing to follow) it was another classic case of the flux leaking voltage but untraceable by continuity tests. I scraped around all of the connections leading to pin 15 on the mux and low and behold I have a working daughter board.

Poking around a little shows this flux m'larkie could be that it draws in moisture from the atmosphere or badly cured FSR boards react with it. It's like snake oil to the manufactures; Chemtronics have a product for thier 'no clean flux' called 'Flux Off' - nasty sods.

Best way to clean seems to be IPA flushed with warm soapy water and your old tooth brush; followed by warm air drying.

For MegaDrum Xtal speeds I think this is all a waste of time.

[kurtus420]

thanks for the tips Ken.