Appliance Repair

Testing DC Signals to the Inverter

Name: Testing DC Signals to the Inverter
Uploaded: 2026-07-07T19:10:38Z
Duration: 2 min 36 s
Description: Learn how to diagnose DC communication and power circuits between the main control board, user interface, and inverter. This lesson explains how to verify 13.5V and 5V DC supplies, understand TX/RX communication lines, and use voltage measurements to determine whether a failed component is caused by the main control board or the connected device.

Learn how to diagnose DC communication and power circuits between the main control board, user interface, and inverter. This lesson explains how to verify 13.5V and 5V DC supplies, understand TX/RX communication lines, and use voltage measurements to determine whether a failed component is caused by the main control board or the connected device.

Hard Skills

Electrical

Maintenance

Juan Morales

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Transcript

I would detach it and measure directly at the bare connector on the main. Check for that thirteen point five volts DC because it is very possible the user interface might be, uh, loading down the board, the main board, if it's def-- if the UI is defective. So that's another way you would be able to tell if you have to change the, the user interface board.

But very, very important that you understand the, the, the test points themselves. Okay. Now, there's two more pins right there, pins number two and three, that carry a TX and an RX line. These are transmit and receive serial data lines, which you will not be able to measure with your multimeter, okay? There's just no way you're gonna be able to do that.

Now, this is what, uh, any time you press a button, like a little square wave gets sent to the main, and then, uh, another signal is received. Uh, the only way you would be ab-be able to measure that is with an oscilloscope, and none of us in the field, right, as technicians, we don't, we don't carry an oscilloscope.

So you are limited to measuring the DC voltage, but that is very powerful in itself to be able to do that. Now, with that, we're gonna go ahead and switch gears, and we're gonna go to the connection between the main and the inverter board. This is critical, my friends, for various reasons. But let's go ahead and, uh, zoom in and take a look at what we have over here.

So here we have two connectors, uh, connector J six oh one that comes from the main control board, and then connector three oh one that is on the inverter. So the two points that should stand out very, uh, very quickly are the five volts and your ground. And let's start with those, okay? If you wanna measure between, um...

Or if you want to measure the five volts, you would go to pin fi- uh, pin number one. That is gonna be on J six oh one on the main or J three oh one on the inverter. Doesn't matter where you measure, but put, put one lead there. You're gonna put the other, other multimeter lead on pin number four. And again, it doesn't matter which connector you go to.

If you measure across those two points, you will get five volts DC, all right? 'Cause you could see it right there, five volts, and it is a DC voltage. Now, this is easy to measure. And again, the reason why this is important is because if the user-- um, not the user interface, sorry. If the inverter board is not doing anything, it is very possible that it is not receiving that five-volt DC signal from the main, okay?

This DC voltage is generated at the main control board, and it is fed to the inverter board. If you have a dead inverter that's, that doesn't want to fire up the motor, it could very, very well be just that five volts. It's not that common, but it is a possibility, so now you know where to measure it.