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Digital Data Communications in Appliances - Samsung Dryer

Samurai Appliance Repair Man

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Most appliances today use computers to control the various appliance functions. Computers talk in logical 1's and 0's which are actually pulses or square waves of voltage that you can see on an oscilloscope or measure with a meter. These pulses are arranged in a specific sequence to transmit and receive information inside the appliance. In this video, the Samurai uses a Samsung dryer to show you what these pulses look like and how to use this information for troubleshooting.

Come with me now on Journey of Total Appliance Enlightenment.

Learn how to troubleshoot appliances like a real technician at http://mastersamuraitech.com

 



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Great video Scott. Especially like the TX and RX info.  Good to know.

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Samurai Appliance Repair Man

Posted

Thanks, Dave. I just want to add, too, that this technology is the same in all appliances, regardless of manufacturer, which use a computer board with one or more sub-boards. This is how these boards talk to each other using serial data communications. The only thing that varies among manufacturers is how they label these lines. But there will always be data lines, DC supply, and DC ground. You can usually identify DC ground and DC supply easily enough. But different manufacturers will use different callouts for the data lines. In this case, Samsung used intuitive labelling and made it easy to know which was transmit and which was receive. It's not always that easy to identify which is which. 

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Yeah, they don't all make it easy like Samsung.  Since not many techs carry an oscilloscope would you be able to explain how to do this test on a voltmeter?  I've encountered situations where I've been able to test DC voltage on comm lines and see fluctuations between 0 and 5 VDC, indicating that communications are occurring, correct? (see thread below)

 

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Samurai Appliance Repair Man

Posted

Correctillia. Just use your DMM at the same test points you would use an o-scope. Your DMM will report an average DC voltage reading back to you, somewhere between 0 and 5 VDC. The closer those pulses are together (higher frequency), the higher the average voltage reading on your meter. As a general rule, any reading above 1 VDC is a pretty good indication that there's serial data communications going on. 

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micabay

Posted (edited)

17 minutes ago, Samurai Appliance Repair Man said:

Correctillia. Just use your DMM at the same test points you would use an o-scope. Your DMM will report an average DC voltage reading back to you, somewhere between 0 and 5 VDC. The closer those pulses are together (higher frequency), the higher the average voltage reading on your meter. As a general rule, any reading above 1 VDC is a pretty good indication that there's serial data communications going on. 

This right here is why a good meter (such as a fluke 116) is needed.  I had to do without my fluke for a few months. My backup meter (Klien MM2000) takes longer to read voltage.  It would just jump around showing no values until the voltage was steady for a half second or more. 

 

Thanks for the educational video! Keep em coming

Edited by micabay

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Samurai Appliance Repair Man

Posted

23 minutes ago, micabay said:

This right here is why a good meter (such as a fluke 116) is needed.  I had to do without my fluke for a few months. My backup meter (Klien MM2000) takes longer to read voltage.  It would just jump around showing no values until the voltage was steady for a half second or more. 

Excellent point and so true! I had this exact same problem with my old Radio Shack DMM-- jumping around and not showing me what was really going on in the circuit. I should have made that point in the video. A DMM will do the job but it has to be a quality DMM. Radio Shack, Klein, whatever, just don't make the grade. 

If you're not going to carry a scope to check data lines, spend the money and get a Fluke. 

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     Did you have the other volt meter probe on ground wire on the same

connector when checking the rx and tx wire? 

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Samurai Appliance Repair Man

Posted

The data on the RX and TX lines are just pulses of DC voltage. So whether you're using an oscilloscope or a digital multimeter, you're still going to connect to the circuit the same way. 

Electrically, an oscilloscope connects to the circuit the same way as your DMM. The only difference is that the 0-scope lets you see a graphical representation of these pulses instead of showing digital readout of the mathematical average DC voltage. But they are both electrical meters so both connect to the circuit at the same two points: the point of interest (RX or TX, in this case) and the reference for the point of interest (DC ground). 

Make sense?

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https://www.linkinstruments.com/logana32.html

This is a cheap ($800... relatively cheap) alternative to a good oscilloscope and is actually specifically designed for this application - observing and logging serial data communication.  What's even cooler about this device is that it is also a pattern generator.  Once you capture a "good" communication protocol you can mimic it with this device to drive OEM peripherals as if you are the OEM motherboard.  

I will say that it takes a lot of patience and finagling to figure out though.

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Samurai Appliance Repair Man

Posted

5 minutes ago, BoardFruit said:

What's even cooler about this device is that it is also a pattern generator.  Once you capture a "good" communication protocol you can mimic it with this device to drive OEM peripherals as if you are the OEM motherboard.  

That's a cool feature. Problem is capturing that protocol because they move around so much. Often takes more time than we usually have on a service call in a customer's home. 

The oscilloscope I used in the video is made by Oscium, model iMSO-204L. It costs about $400 and connects to my iPad (which I always have with me on service calls anyway) so it's very little overhead in terms of extra equipment to haul into the house on a service call-- fits nicely into my tool bag. 

My use for o-scopes in service calls is mostly to check for the existence of a "pulse" on data lines that should be active. The DMM gives a rough approximation of this by reporting an average DC of the pulses and/or a frequency. But it's cool to see the actual pulses. It's like watching red blood cells in action! 

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8 minutes ago, Samurai Appliance Repair Man said:

That's a cool feature. Problem is capturing that protocol because they move around so much. Often takes more time than we usually have on a service call in a customer's home. 

The oscilloscope I used in the video is made by Oscium, model iMSO-204L. It costs about $400 and connects to my iPad (which I always have with me on service calls anyway) so it's very little overhead in terms of extra equipment to haul into the house on a service call-- fits nicely into my tool bag. 

My use for o-scopes in service calls is mostly to check for the existence of a "pulse" on data lines that should be active. The DMM gives a rough approximation of this by reporting an average DC of the pulses and/or a frequency. But it's cool to see the actual pulses. It's like watching red blood cells in action! 

Oh cooool!! Yeah I've always wanted to try one of those iPad scopes - glad to hear it works well.  You can't beat $400 for a well-functioning scope.

Yeah I guess the logic analyzer isn't so great for service calls - lots of set up.  I love the idea of chip-level diagnostics on appliances tho.  Anybody taking these techniques with them is definitely on their way to true enlightenment.

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