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Hi,

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I recently finished building my qmx and after checking for shorts and not finding any I plugged it in but it draws too much current (200mA when applying 7V (which drop to 3.7V)).

I can connect to the device via the serial console where it outputs the following data:

Supply
Voltage: ? ? ? 3.7 V?
5V SMPS
Status: ? ? ? ?Error
Voltage: ? ? ? 3.34 V
Duty max: ? ? ?85 %
Duty cycle: ? ?85 %

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The 3V3 SMPS is working fine.

When testing the 5V SMPS board it seemed to work.

Any ideas where I should start looking?

Cheers
Lieven DF1CN

I'd start by removing the SMPS boards and running the Power Supply Test Process described here /g/QRPLabs/wiki/37128?on them.

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It seems that there's something pulling the 5V VCC line low, one possibility is the Zener diode designed to protect the 5V supply.? The power supply tests will show this.

There's also a possibility that VDD, the 3.3V supply is drawing too much current.

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When you say the 3.3V SMPS is working fine do you mean that it's switched to SMPS mode and the duty cycle shows a reasonable value?? If it's still in linear mode then the current will be higher and increasing the current limit slightly may help.? Up to 250mA, not more.

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Chris

The 5V SMPS cannot work if the supply voltage is 3.7V, and would show data just like what you provided.

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So it is impossible to tell if the 5V SMPS has a problem in this condition.

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Please post a screenshot of the diagnostics page so we can see the data for the 3.3V supply (need to see duty cycle and state).

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I would also increase the current limit to about 250mA and see if the situation changes.? At lower voltages (7V), the controller may require a bit more current to start up everything before firmware is loaded.

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But since the voltage is limiting to 3.5V, it seems that you may have a short somewhere.? It may be on your main board; have you checked the resistance between each voltage rail and ground?? Should be a few k-ohms on each, and also several k-ohms between each of the voltages.? Also check visually for anything on the display/control boards that could be contacting where they should not - there are several places with minimal clearance that could be shorting.

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Stan KC7XE