Big OOPS! day...

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AlbertHall

Joined Jun 4, 2014
11,594
This morning I was assembling components onto a PCB that I made. Then I began testing it by applying a low voltage (2V) to it. I discovered that there was no voltage at all (0.00V) coming out of the bridge rectifier on the power input. The output was not short circuit but careful inspection revealed that I had fitted the bridge backwards! So I attempted to remove it from the board and in the process ripped two tracks off the board. I refitted the bridge and added two link wires to replace the broken tracks and started testing again with the 2V input. The next thing the gets to is an LM317LM voltage regulator. It had an input but 0V output. Inspection revealed (yes, you guessed it) I had fitted this chip the wrong way round too. I managed to remove and replace this without damaging the board and began testing again. All seemed well so I decided the next thing to do was to try and program the PIC on this board.

I got out an old USB hub and connected it to the computer but it needed an external 5V supply so I rummaged in my collection of wall warts and found a 3A one which ought to be sufficient. Connected that up and plugged in the PICKIT4. The PICKIT4 released the magic smoke and was very hot. The USB hub was hot too. The supply I had connected was 3A, but it was 12V not 5V.

The PICKIT has two obviously burnt components.
U1 - a MIC2044 iY2S high side switch chip which is available.
A six pin chip which looks like a SOT23-6 but has no visible marking and no component reference. I can find no schematic for the PICKIT4 so I guess it is now scrap.

I guess the USB hub is scrap too as it has a SOIC8 chip with a bulge on top and no readable markings.

I think I should have stayed in bed this morning.
 
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