Let's say you're working on a Samsung washer that won't power on at all, and you run into an unexpected troubleshooting roadblock: it seems like the schematic and the pinout don't line up. How do you deal with a situation like this? Let's take things step-by-step and see if we can't figure it out.

For an unresponsive appliance like this, you would first want to make sure the main control is getting power. Any control board needs its own unswitched Line and Neutral power supply. Usually, these are pretty easy to locate. Let's look at the schematic:

Neutral goes straight to the power relay on the board, and Line tags off the heater relay before heading to that one-pin connector to the right. Seems easy enough! We just need to find those relays and do our testing there.

However, when you actually look at the main control board in the real world, you would see something like this:

This is what we call a pinout -- a picture of the physical control board with all the connector pins labelled. These are often essential for troubleshooting, especially when the schematic tells you nothing about what's on a particular connector.

But something is off here -- where are those two relays we saw on the schematic? We do at least see that one-pin connector that receives our Line supply:

And if you look closely in that area of the control board, you'll see something telling: two relays that aren't labelled. 

One mystery solved! No idea why they didn't bother labelling the relays, but all you would need to do is put your multimeter on the LoZ setting and read from CN101 to each of the relay pins until you get 120 VAC. Once you do, you know you've found your Neutral on pin 1 of the power relay. And if you don't get 120 anywhere, then you have identified a missing power supply to the main control.

That's all well and good, but let's say you do find that the control is receiving power. What now?

Our attention should turn next to the UI. If there is some problem there, then we won't get lights or action of any kind from the washer.

The best way to troubleshoot this is to test our DC supplies going to the UI from the main control, specifically the DC power supply and the digital data communications lines between the two boards.

However, while the schematic shows the connector, it doesn't tell us anything about what's on them. So let's go to the pinouts again, this time for the UI itself. All we need to find is that one 7-pin connector.

Huh, that's weird. There are a bunch more connectors on this UI than the schematic shows, and none of them has exactly 7 pins. What gives?

Well, it looks like a lot of these connectors are for programming the board and for optional peripherals. But one of these connectors is in fact the one we're looking for -- you just have to look closely.

CN3, while it physically has 10 pins, only actually uses 7. 1, 2, and 10 are all unused. They're marked as NC, or "Not Connected," meaning there's nothing on them.

Now we're getting somewhere! To test the DC power supply, we just need to read from CN3 pin 8 to pin 7 -- that's our 12 VDC supply to DC Ground, as you can see on the pinout.

But the DC power supply isn't enough -- we also want to check if the boards are talking to each other. For that, we'll want to check the pins labelled "TX to Main" and "RX from Main." TX means "Transmit" and RX means "Receive." Those are the lines where the boards are sending data to each other.

Here they are marked on the schematic, with TX marked orange and RX marked yellow.

All you would need to do is read from CN3 pin 3 to DC Ground to check if the UI is receiving data from the main board. There's no real spec for this -- you just want to see some small DC voltage there. Your meter will usually show something in the range of 2-3 VDC. And you can do the exact same thing with the RX line on pin 4.

There you have it -- the manufacturers don't always make it easy, but even when they don't print the cleanest documentation, a little study and a little know-how can lead to a rock-solid troubleshooting plan.

Want to get in on the action? Join the Brotherhood of Techs at Appliantology.

• Appliantology.org is a cultivated, private community of techs.
• Get solid tech advice from working, professional techs and business owners.
• Avoid the endless noise and guesswork thrown at you from groups on social media.
• Download the service manuals, tech sheets, and service bulletins you need to git 'er done.

Join the Brethren in the Craft right now with our membership options at Appliantology and see how it can help you in your business starting today.