VPP Problems (PIC)

[UTMonkey]

Hi All,

I have a PIC that has suddenly become unresponsive. the PicKit2 software diagnostics report a problem with VPP.

If I unplug my Junebug and test VPP it passes, insert it back into the circuit it fails reporting a short.

I have removed the MCLR pullup and the problem persists - take the PIC out of the circuit and test and it passes.

So it looks like it is definitely something to do with the PIC, have I locked it up??? how can I unlock it?


Thanks in advance.

Mark

 

[blueroomelectronics]

It may be too small a pullup on MCLR. Connect the VPP without a pullup and use the Junebugs built-in pullup (dip switch 1 on)

 

[UTMonkey]

Hi Bill, thanks for the response.

I have done as you suggested, unfortunately it hasnt made any difference.

I doubt I have killed my PIC - just confused it.

Is their some kind of re-initialisation process I can perform?

Regards

Mark

 

[futz]

Quicky breadboard it and erase it with the PICkit 2 software? You've probably already tried it, but maybe not?

When I was unable to connect to or reprogram a few PICs with MPLAB, because I had turned on the Timer1 clock, that was the only thing that would get them working again. Even then they had to be PICkit 2 powered. Target power had to be off or it wouldn't work.

Or use the "hammer and coins" method. Put the PIC on a rock and hit it hard with a hammer so you can see its insides. Verrry interesting! Use the coins to buy a new PIC.

 

[UTMonkey]

Hi Futz,

Unfortunately I get the error before any connections takes place.

I could do with a few more suggestions before I resort to "Hammer and Coins" ;-)

Thanks for the advice

Mark

 

[3v0]

Try connecting to a know good chip of the same type, swap in the bad chip, then erase without reconnecting.

It may be worth a try.

 

[UTMonkey]

Thanks for the suggestion 3V0.

I do have 3 more 18f2550's so I did as you suggested, get PicKit2 to recognise a good chip (which it did) and then swap it with the "confused" chip to erase (which unfortunately it didn't).

I was always told it was pretty difficult to kill a PIC, and to say that previous to this happening I was happily debugging the chip fine makes this slightly strange.

Throw the "confused" chip in the garbage?

Mark

 

[mvs sarma]

Thanks for the suggestion 3V0.

I do have 3 more 18f2550's so I did as you suggested, get PicKit2 to recognise a good chip (which it did) and then swap it with the "confused" chip to erase (which unfortunately it didn't).

I was always told it was pretty difficult to kill a PIC, and to say that previous to this happening I was happily debugging the chip fine makes this slightly strange.

Throw the "confused" chip in the garbage?

Mark

Once I killed the same type chip trying to program pickit2 firmware while assembling the Junebug. Ofcourse I was trying to use a local PIC pppppprogrammer of JDM type with external supply.On suggestions from Bill, the proud designer of Junebug, and help of another friend who had a PICKIT2 and I could program a second chip. made possible by interconnecting un-programed PIC18F2550 on Junebug , to Pickit2. The faulty chip becomes too HOT as I connect Vdd and Vss.

Instead of Rock&Hammermethod, I decided to keep it on my work bench, to remind me of possible failures, unless done cautiously and methodically.

 

[Boomslang]

Thanks for the suggestion 3V0.

I do have 3 more 18f2550's so I did as you suggested, get PicKit2 to recognise a good chip (which it did) and then swap it with the "confused" chip to erase (which unfortunately it didn't).

I was always told it was pretty difficult to kill a PIC, and to say that previous to this happening I was happily debugging the chip fine makes this slightly strange.

Throw the "confused" chip in the garbage?

Mark

Connect 24V to the "confused" chip... if no smoke comes out it must be broken already... if smoke does come out..you just broke it...

 

[futz]

Connect 24V to the "confused" chip... if no smoke comes out it must be broken already... if smoke does come out..you just broke it...

Sounds like how we forecast the weather here where I live.

You look out the window at the mountains. If you can see the mountains, it's going to rain. If you can't see the mountains, it's already raining!

 

[Krumlink]

You won't be able to fry a PIC so easily. I have connected power backwards and 12VDC. It is now one of my Junebugs, and I have never had a problem with it yet. Hardy little buggers, with I could say the same for some of my 74HC's