Sunday, December 18, 2016

Built additional boards and tested them, ready to connect power and run the Diablo


I began to build a second driver board, but after putting on the resistors and preparing to install capacitors, I found the VCC and ground lines were shorted. I couldn't find any spot that seemed to be causing the problem, even after lifting as much solder as I could off the board. I put it aside as a potential bad board.

Taking a third PCB card, I did a full installation of all components, with no signs of shorts or other problems. It still must pass the wiring and correct operation tests, just as the first board I built must. The first board passed all its connectivity tests by mid afternoon, then I went back to the bad board so see what is wrong.

Board 1 installed on the extension board
To ensure that it wasn't a solder bridge under one of the resistors or the power connector, I removed them all and used solder braid to wick off as much solder as possible. The board continued to show that all four pins of the power connector were bridged together, thus shorting +5V, +3.3V and ground. It is unusable.

Board 2 with shorted power connector pins - unusable

I put the third PCB (2nd is bad) on the test bench. All the connectivity and short circuit tests were passed, visual inspection is good too. All that remains is to power it up and check the function of the drive with the fpga logic.

Board 2, in place waiting for power connector hookup
I mounted the driver PCB board on the extension board and hooked that to the fpga, ready to test as soon as I wire up the main power connector. Instead of wire nuts hooked to the existing power supply connector, I will make up a proper cable which bridges between the PC power supply main connector, that would normally be plugged onto a motherboard, and the four pin connector to drive my PCB.

Power supply connector
One wire has to be connected to ground to 'turn on' the supply, and the power resistor you see on the bottom has to provide a load in order for the supply to work, but many of the voltages supplied are unneeded. All it will take to build this is an ATX power supply plug, some heavy wire and a 4 pin Molex plug for the other end. 

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