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Using Frequency Measurements as a Troubleshooting Tool

Son of Samurai


Here's our scenario: you're working on a Samsung WA50K8600AW washer that won't advance in the cycle. Error codes and test modes aren't telling you anything useful, and the control doesn't even seem to be trying to advance the cycle. You've checked the air tube connected to the pressure sensor, too, and everything is clear there.

What can you do here? Do you just call it a bad board and move on?

Let's see if there's a smarter test we can do on this one. What if we could test the signal that the pressure sensor is sending back to the board? Well, let's look at the schematic.

Screenshot 2021-02-10 192557.png

Not too helpful. Sure, we can see that one of the wires connected to the pressure sensor is a ground wire and the other two are signal wires. But if we measure across those two signal wires, what would we expect to see? The schematic doesn't tell us.

But maybe somewhere else in the manual does...

Screenshot 2021-02-10 184316.png

Aha! There we have it -- the all-important spec. But here's the catch: it's not a voltage or resistance spec, like what we're used to measuring for. This pressure sensor communicates with the board via a frequency signal.

I don't know about you, but I don't measure frequency very often. But that doesn't mean there aren't ways to measure it! In fact, a lot of multimeters, such as my Fluke 116, are perfectly capable of doing a frequency measurement.

Here's a pic of my meter while I have both leads in a wall outlet. You can see it's showing a solid 60 Hz, as you would expect for a normal household power supply.


It's that easy -- if your frequency measurement on the pressure sensor is out of spec, then you know you've found your problem. Here's a picture of actually taking the measurement:


Want to learn more about making measurements with your meter and interpreting the results? Click below to watch a webinar recording on exactly that -- available only to premium members.

Screenshot 2021-02-10 194507.png

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I actually just performed this test a few weeks ago. Never needed to check frequency before but was happy to see my meter had that. Pressure switch tested good by this test an ended up being an out of balance sensor and harness but it was a good learning experience for next time. 

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The manual portion above shows Blue to Orange as testing points, but the diagram shows blue, pink, and green? Would I be correct if I said the testing points should be Blue and Pink approximately 26.4KHz?

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Son of Samurai


3 hours ago, JohnnyCage said:

The manual portion above shows Blue to Orange as testing points, but the diagram shows blue, pink, and green? Would I be correct if I said the testing points should be Blue and Pink approximately 26.4KHz?

You got it! You'd want to measure across the blue and pink wires.

You see errors like that pretty often, especially in dummy directions, and even more especially in Samsung and LG documentation. That's where we as the techs have to use our know-how to surmise what the correct test locations have to be.

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  • Team Samurai
Samurai Appliance Repair Man


2 hours ago, Son of Samurai said:

dummy directions

For others who haven't heard that term before, we show an especially egregious example of dummy directions in an LG service manual and how to avoid being head-faked by them in this webinar recording

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