Reason for the failure of the pic when powered on

[gauravbijlani]

Dear Sir/Madam,

I am an Analog Test Engineer and sometimes,there are tricky issues or problems.The other day,I plugged in the unit that our company manufactures and there was a puff of smoke.

I checked the wiring,it was alright.Anyways,I checked the fuse and it was blown out so,I changed the fuse.When I powered the unit on again,it drew a lot of current and on extensive fault finding by me and my colleague,we came to a conclusion that the PIC had blown.

When it blew(we couldnt see it but it was the only part of the circuit we could think of),it created an internal short and it drew a lot of current.Why ?

Besides,PIC's do not blow without improper wiring which was not the case in my case so why did it blow?

Thanking you,

 

[elMickotanko]

When it blew(we couldnt see it but it was the only part of the circuit we could think of),it created an internal short and it drew a lot of current.Why ?

Ive been having similar problems lately. I got help here suggesting that when transistors blow:

Yes, the semiconductor junction fuses together forming one big conductor

This happened to me with my transistors and also a couple 7404 logic chips.
The voltage regulator got really hot so i took out the 7404 - I measured 70 ohms between its Vs and GND pins! Not sure why it happened in the first place though.

 

[OutToLunch]

Are you sure the pic blew first? Perhaps some other component had failed and that caused the fuse to blow. When you replaced the fuse and powered back up, the fault could then go have gone to the pic. You should have investigated the board prior to replacing the fuse.

 

[Nigel Goodwin]

PIC's are VERY reliable, and even take considerable abuse - for blowing a fuse I would tend to look elsewhere first?.

However, and I presume you would have checked for this?, are you sure the PIC is fitted the correct way round? - if not the internal protection diodes short the supply (two diodes in series across the supply). They get red hot like this, and can even burn your finger prints into the top of them! - don't ask how I know! (the PIC still works by the way!)

 

[RODALCO]

Check the voltage regulator on the board first.
It could have failed and the supply voltage is a lot higher hence the smoke.