This is a very unusual chip to blow like this. Just like with the blown driver chip, damage like this indicates a LOT of power. But this chip is nowhere near any high voltages.
The Diagnosis
- Assembly error? Nope. This was an assembled PRO board, so it was fully tested prior to shipment.
- The board had two stepper motors connected and power added. The motor current was set and the motors locked. Good.
- When the board was connected to the PC, the chip blew.
- Primary suspect #1 – some issue with the power supply, perhaps some voltage to the chassis causing a lot of current through ground. Supply was a cheap 36V 10A Chinese switching supply, that measured 36 volts between the chassis and the V-. This seemed odd to me, I’d prefer the V+ and V- outputs to be isolated from the chassis.
Side Note: You can see a cheap Chinese vs. quality power supply here: https://www.youtube.com/watch?v=rJ2SiBzijiw. It’s 15 minutes and worth the watch. - What about the cable from the HobbyCNC PRO to the PC?
a. The customer did not purchase the parallel cable from me.
b. Turns out the customer purchased a serial printer cable. Only half correct. The PRO requires a parallel printer cable, all 25 pins, wired straight-through.
So, I’m not 100% certain is wasn’t the power supply, but at this point, my money is on the use of the serial printer cable.