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jmamma / MegaCommand_Design

MegaCommand MIDI Controller
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MCL / button and encoder test fail #12

Closed zerkalo06 closed 3 years ago

zerkalo06 commented 3 years ago

Hello Justin and Yatao,

I create this issue after having a conversation with Justin on the elektronaut forum.

At first I had a problem with the sram test, but now after reflowing the ic everything is fine. I then tried the button and encoder test and I got nothing from the serial monitor, so I checked the SN74LS165AN chips and I got those results (those are in volt of course, even tho I didn't specify it) :

Results megacommand top_bottom

I maybe have to check again and de-solder again the male headers as I don't get the same results from those now, 0v all across apart for 47 and +5. Maybe it's just due to the amount of solder, my voltmeter is not that great. Isn't it strange the sram test is still working ?

Here are the pics of my pcb (I replaced one 0,1uf capacitor missing by another ceramic one I had left) :

20201124_161247 20201124_161258

Thanks for your help, and great great work you doing here !

jmamma commented 3 years ago

Okay good to know that.

On each resistor array ( R1 and R2), the pin closest to the bottom of the board should read 5V with respect to GND.

This is the supply voltage to the resistor array. Can you verify that it is constant. It should read 5V without rotating encoder or pushing button.

zerkalo06 commented 3 years ago

The supply voltage is constant on the two resistor array but only reading 3,7v or 3,9v depending if the board is powered by a computer or a electrical outlet.

jmamma commented 3 years ago

Understood.

Can you measure the 5V voltage being supplied by the Arduino Mega.

When the MegaCommand board is viewed from above, the double header has GND, and 5V labeling.

(Top 2 and bottom 2 pins of the double header.)

zerkalo06 commented 3 years ago

I get 4,8v from both double header.

jmamma commented 3 years ago

Okay. There's another 5V supply rail that comes off the right most Arduino header in the middle of the board. It powers R1 + R2, and all of the ICs.

I suspect this rail is being dragged down by a failing component. I have a strategy for narrowing it down.

Just putting together a diagram.

jmamma commented 3 years ago
5V

The RED line is the 5V supply rail that is shared amongst the ICs.

jmamma commented 3 years ago

All the elements are connected in parallel, so unfortunately each node along that path will measure the same voltage. You measured it at approx 3.7 V.

jmamma commented 3 years ago

What we know:

SRAM is working. It can run on a supply voltage as low as 2.7V The Octal latch is working. It must be if SRAM is working. It can run on a low 2V supply voltage.

The shift registers require 4.7V to run. Either one of these could be faulty.

Optocouplers require 4.5V. Either of these could be faulty.

R1 or R2 should be okay, given your voltage + button test above. Double check each pin on R1 and R2 should read 3.7V (5V with a working board) and change to 0V when corresponding button is pressed.

jmamma commented 3 years ago

So the only option here is to start replacing components connected to the 5V rail. Unfortunately because you soldered up the MIDI circuits, you have two extra ICs that could be to blame.

1) Shift registers. 2) Optocouplers* 3) Capacitors that are on the 5V rail. <-- easy starting point.

jmamma commented 3 years ago

So the procedure is:

a) Remove component. b) Test the 5V rail. c) If 5V rail voltage is measuring 5V you know you've found the problem component.

zerkalo06 commented 3 years ago

Hey Justin and Yatao ! Just to let you know I've finally manage to finish my mcl. Thanks so much for your help ! Silly mistake I just forgot to put the middle male headers ... So anybody passing by just take time to verify everything, and don't hesitate to let it sit for a time and come back to it with a more clear vision. Thanks again for all the work you're put into the mcl and md projects !