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I've been given a motorised sit-stand desk (Flexispot brand) that the previous owner had replaced because the motor didn't work. I suspected there was a short somewhere in the motor because plugging it into the controller made the controller screen go blank. I've opened the motor up and there's a small circuit board inside with an obviously broken diode labelled D1 (with a big crack where the magic smoke must have come out...

The markings are "PKJH 6V8A" and a cathode line (see image). Searching for 6V8A returns two types of matches - Zener and TVS diodes - any ideas which of the two this might be? Or am I on the wrong track completely? Thanks!

motor circuit board image

close-up of the broken diode in question

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  • \$\begingroup\$ Those beefy packages are typical for TVS. I think they are called DO214A \$\endgroup\$
    – tobalt
    Commented Nov 3, 2021 at 18:45
  • \$\begingroup\$ Looks like a TVS but I'm willing to bet that replacing the diode won't fix the problem. Clearly something dumped enough energy in there to crack the case so even though they're supposed to protect downstream circuitry, it might not have succeeded totally. And then there's still the question of how the TVS got overloaded in the first place. \$\endgroup\$
    – vir
    Commented Nov 3, 2021 at 18:48
  • \$\begingroup\$ This appears more like a slow-cook than a sudden failure to me. I'd bet Zener. Looks like an (obviously inadequate) poor mans voltage regulator. R4 (R5?) is seemingly quite cooked also, and is connected to the cathode, which further suggests "regulator" (to me at least...) I'd replace both with physically larger parts, same specs (i.e. a 1/4W resistor and 1/2W zener). Will take some creative soldering to do so. That resistor BTW is likely NOT 100 ohms - It would be 10 ohms. There are others marked "100", you can possibly measure them to be sure.... \$\endgroup\$
    – Kyle B
    Commented Nov 3, 2021 at 21:06
  • \$\begingroup\$ Luckily I received a pair of controllers and power supplies with this - one of the controllers was also broken, and there's a burst IC on that board also, so plenty of other things to check... The resistors labelled 100 are indeed 10 ohms. The board is covered in some kind of lacquer that covers the smaller components and pads so I'll try and scrape some off to measure R5 - I think it looks worse in the picture with its black 'halo' but I wonder if that's just residue from the burn \$\endgroup\$
    – jsavn
    Commented Nov 4, 2021 at 9:59

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Searching just for the marking 6V8A yielded too many results, but I found the name of the manufacturer (BrightKing) in a different question on this site with a similar branded part (another TVS diode from same manufacturer, and searching for brightking 6v8a brought up the relevant datasheet: datasheet for the TVS diode in question. It is indeed a unidirectional TVS diode, and I can try finding a replacement part now. Whether it will work is another question! (and the comments don't inspire much optimism...)

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