Could my 28x have survived

[Tim Vukman]

In my excitement to get started with my new Pic 28X I accidently hooked my power suuply line on the unregulated 12v side of my power supply instead of on the 5v side.

I have not been able to communicate with the 28x and I figure I probably burned it out with the 12v.

It was connected to 12v for probably 30 seconds.

I have ordered a new one but thought I would ask just in case the 28x might have survived and I therefore have a circuit issue.

Thanks

TimV

 

[ylp88]

Unfortunately, probably not, but it may be worth checking a few things just in case by some miracle it still works.

Overvoltage and overheating can often be seen by looking for hairline fractures on the chip, usually on the surface which has all the writing on it. You WILL need a magnifying glass to do this. If there are, it is a very bad sign.

Try hooking it up with the most minimal setup: user 3 x 1.5V AA and the two download resistors.

Failing this, it may be time to wait for your replacements to arrive.

<b><i>ylp88 </b> </i>

 

[SD2100]

Hook up as ylp88 says with 3 x 1.5V AA and the two download resistors. Also connect the 4.7k reset resistor from pin 1 to 5v and fit the 4mhz resonator. You might be lucky.

 

[Tim Vukman]

Thanks for the response and the suggestion.

I have carefully examined the surface and I don't see any damage.

I will try the minimal circuit and respond wih the results.

I currently have pins 21 - 28 wired to LEDs through 330R and pins 11 - 18 tied to ground through 10K resistors. Should I disconnect or maybe pull the chip to test?

Thanks

Tim

 

[pbunyan]

yes, i would remove the leds and resistors, and just try it with the components it needs to run, and see if the PC will connect to it

one good way to check is if it is dead, it will most probably start to heat up straight away when you power it up, thats what several of my chips did after they had died.

 

[Tim Vukman]

I have created a new circuit for the 28X that has only the 22K and 10K resistors.

I do not get a response from the 28x when I try to connect.

The chip iteslf is not heating up. It might be slightly warmer than room temperature but it is hard to be certain.

When I &quot;run&quot; the program to the chip, I have a voltage swing on pin6 (chip side of 22K) from -.53v to +10.63v

Pin 7 never moves off of +.26v.

My 3 pin resonator did not survive removal from the previous circuit. I do not have another right now. I tried using a 2 pin
(the package said 4mhz (Pn B55 E20)) so I have either confirmed that the 28x is dead, or I can't confirm for certain until I get another 3 pin resonator.

The help and suggestions are certainly appreciated.

Timv

 

[hippy]

<i>When I &quot;run&quot; the program to the chip, I have a voltage swing on pin6 (chip side of 22K) from -.53v to +10.63v </i>

That does sound like the chip is damaged.

There are internal diode clamps to the +V and 0V so voltage measured should never exceed about +5.6V, or go below about -0.6V. The negative clamping appears to be functioning but not the positive clamping, which suggest the diode has been blown away.

 

[Tim Vukman]

Thanks for seeing this through with me. I will wait for my new chip and start over

All is not lost. With your help I learned a few things !

Tim

 

[evanh]

Well, if there is nothing stopping the power rail rising to 10 volts via the internal diode then that's exactly what will happen. As for heating, I can't say for sure what the picaxe will do.

One thing that is a very common behaviour of overvolting an eprom is you erase them. I can imagine flash memory being even more likely to do this. And that includes the firmware for downloading to a Picaxe.


Evan

Edited by - evanh on 18/04/2006 14:39:24