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I have purchased some USB-C connectors that I use to build my own cables with (I have separate "host" and "device" side connectors for various cable assemblies), and I was wondering how I might go about testing the resistor on the little PCB to ensure it is correct and to spec? Any best practices or reliable techniques for doing this?

I recently had a customer inform me that a USB-C to Mini-USB cable that I made for him damaged the keyboard he had it plugged into and I'm trying to ensure it doesn't happen again. (I am assuming there was something wrong with the USB-C resistor that caused the issue). Thanks!

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  • \$\begingroup\$ Which side was Type-C port on? On the keyboard, or host? \$\endgroup\$ May 7, 2018 at 5:41

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How to test Type-C end of cable? You buy a breakout board like this one or similar, with Type-C receptacle,

enter image description here

and then use DMM to measure resistance on both CC pins, to ground, and to VBUS.

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  • \$\begingroup\$ Thanks for the tip. The Type-C connector was on the host side (a MacBook). The client has since tested another keyboard PCB with a different cable of mine with similar results (fried PCB). So it seems like the issue may be with the laptop's USB receptacle? My USB-C connectors have the proper 5.1k pull-down resistors, so I'm not sure what the issue is. Doubtful that it's separate faulty resistors. Would the customer's up-to-date MacBook OS beta, or the MacBook hardware itself be causing this issue? \$\endgroup\$
    – rockwell
    May 8, 2018 at 5:11
  • \$\begingroup\$ @rockwell, It is very-very unlikely that MacBook has a problem with Type-C. I would say impossible, Apple is not a company that can put out obvious flaws. If there is a 5.1k pull-down in your cable, the MacBook will output 5V safe voltage, that's it. If there is no resistor or a pull-up, there won't be any voltage on VBUS at all. Which "another keyboard PCB" your client is complaining about? Bring it here. Again, what stopping your client to plug your cable alone, and measure VBUS on micro-B end? \$\endgroup\$ May 8, 2018 at 5:53
  • \$\begingroup\$ This is a retail end-user so I don't know if they'd be able to test that themsleves, but I have asked for the cables back so I can test. If I want to measure the VBUS coming off of the Mini end, can I just plug it into a little breakout board and pull the measurement off that? Would that be different than putting a little voltage meter inbetween the host USB-C receptacle and the USB-C host plug of the cable and measuring it there? Thanks again. \$\endgroup\$
    – rockwell
    May 8, 2018 at 15:15
  • \$\begingroup\$ @rockwell, yes, you can use a similar breakout board for mini-B side of your cable, and measure the VBUS voltage without any device attache, because it is not any Power Delivery or other active system. \$\endgroup\$ May 8, 2018 at 15:37
  • \$\begingroup\$ Just to follow up, I had my customer test the MacBook's USB receptacles with a power tester, and the results he sent back was: "One of the ports says 20v with fluctuating amps, another says 5v"...this laptop shouldn't be outputting 20v (!), am I correct? \$\endgroup\$
    – rockwell
    May 9, 2018 at 22:45

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