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Son of Samurai's Blog

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Identifying Power Supplies on a Samsung Control Board

Son of Samurai


See if you can identify two things on this Samsung dishwasher schematic:

1. Where does the control board receive line and neutral?

2. Where do the sub-control boards get their DC power supply?

Screenshot 2020-11-19 202107.png

The answer to the first question can be found easily enough, if you have a little schematic reading experience. But it's a bit trickier for those who don't have as much practice.

For one thing, line and neutral aren't explicitly labeled. Just wire colors are given, but fortunately, we can figure some things out based on those. Conventionally, at least here in North America, the line wire is black and the neutral wire is white. Knowing that, we can just trace them out.

InkedScreenshot 2020-11-19 202107_LI.jpg

Wow, neutral took us on quite the journey there! But it does eventually arrive at the control board without passing through any loads.

Question #2 was sort of a trick question. Just by looking at the schematic, we're not actually sure exactly which pins the DC power supply is on. However, we know a couple of things. 

The DC power supply for the sub boards is produced on the main board -- that's just the way multi-board configurations like this work. The main control rectifies the line voltage that it receives into DC power and uses that to power the sub boards. Second thing: we have to be able to measure that DC power supply on CN102 somewhere, because that's the only connector that goes to the sub boards.

Fortunately for us, we can find out exactly which pins to look at by looking elsewhere in the Fast Track for this model. This pinout shows all -- look at the label for CN102.

Screenshot 2020-11-19 202143.png

We actually have two different DC voltages here -- 5 VDC and 12 VDC, on pins 1 and 2 respectively. And we know that pin 6 is DC ground, since that's the one that both voltages are measured with respect to.

Want to learn more about troubleshooting control boards and computer-controlled appliances? Watch this technical webinar that we've recorded just for you -- available only to premium members of Appliantology.


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