Current drops when I attach GNDA

Hi

I have designed me a MUX-PCB (on the right) and a Mixer-Channel-Strip-PCB (the right one).

I can initialize the MUX-PCB correctly and all works fine… it has some Vcc/GND/GNDA-out-pins, so my other PCBs can draw power from them… when I measure the current on those pins, I get 3.3V, which is correct.

When I now attach the Mixer-Channel-Strip-PCB to Vcc/GND … everything cool so far… but now I attach to GNDA, so I can read the analogValues on the potentiometers, and now the current drops to ~2.8V… when I unconnect GNDA the current rises to 3.3V.

has someone a quick idea how i could debug it? or what could cause this?

“MUX-PCB (on the right)” “Mixer-Channel-Strip-PCB (the right one). ”
Do 2 rights make a wrong?

“now the current drops to ~2.8V”

We have no schematic.

We have no idea what you are talking about.

Current measurement does not give a reading in voltage.

"MUX-PCB (on the right)" "Mixer-Channel-Strip-PCB (the right one). "
Do 2 rights make a wrong?

"now the current drops to ~2.8V"

We have no schematic.

We have no idea what you are talking about.

Current measurement does not give a reading in voltage.

What he said

(Larry: "Can't he think of his own replies ! ?")

larryd:

“MUX-PCB (on the right)” “Mixer-Channel-Strip-PCB (the right one). ”
Do 2 rights make a wrong?

“now the current drops to ~2.8V”

We have no schematic.

We have no idea what you are talking about.

Current measurement does not give a reading in voltage.

Oh sorry, I was too quick :confused:

i meant the Mixer-Channel-Strip-PCB is the left one.

I attached the schematic .. it simply is a collection of some potentiometers, switches and RGB-LEDs.

with current, I meant the voltage (shoot me)

mkaPcbPartTracks.pdf (99.5 KB)

BANG!

Your power supply sounds like it maybe underrated.

You may have to cut some traces to see if too much current is being drawn by: a faulty component, miss-wiring, design flaw, solder bridge, faulty fader, or ‘high’ resistance un-etched copper filament.

What's with the GNDA (Analog GND) ?

Why do you have a separate GND for analog ?

What arduino are you using ?

Have you ohmed out the circuits that use GNDA for shorts ?

What is the total resistance you have across the 3.3V with all those resistors ?

You may have to cut some traces to see if too much current is being drawn by: a faulty component, miss-wiring, design flaw, solder bridge or 'high' resistance un-etched copper filament.

Before you cut anything you might want to take the time to ohm everything out for shorts.
Also measure the resistance from 3.3V + to GND BEFORE and AFTER connecting GNDA (with the power off of course)

raschemmel:
What's with the GNDA (Analog GND) ?

Why do you have a separate GND for analog ?

the GND is for the digital readings (switches and encoders) the GNDA is for analog readings (potis) .. I was told to make it so in the teensy-forum.

raschemmel:
What arduino are you using ?

no Arduino, I use a Teensy 3.6 for this.

raschemmel:
Have you ohmed out the circuits that use GNDA for shorts ?

What is the total resistance you have across the 3.3V with all those resistors ?

Before you cut anything you might want to take the time to ohm everything out for shorts.
Also measure the resistance from 3.3V + to GND BEFORE and AFTER connecting GNDA (with the power off of course)

I searched the translator for "ohm out" in german but I can not find it. how does ohm out work?

Hast du den Widerstand gemessen?

The problem is that you ever operated it without GNDA connected - that sort of thing can damage
components. All the ground and power rails should be connected before ever powering up a board
unless you have definite information to the contrary. Without a power or ground rail in place you get
phantom powering, currents flowing where they are not supposed to (possibly burning out components
in the process).

MarkT:
The problem is that you ever operated it without GNDA connected - that sort of thing can damage
components. All the ground and power rails should be connected before ever powering up a board
unless you have definite information to the contrary. Without a power or ground rail in place you get
phantom powering, currents flowing where they are not supposed to (possibly burning out components
in the process).

this would make sense.. i have a few of those PCBs as I had to order min 5 pieces.. so I assambled a new one and checked if voltage drops on every new component added.. it was then finished and all is good now.

thank you very much :slight_smile:

so I assambled a new one and checked if voltage drops on every new component added

Don't do that, it is a great way to damage components.