I think i fried my board

Hello! And happy new year!

Not so happy for me today - I think I blew the chip on my Melzi!

I finalised the assembly yesterday and get the head to 50 degrees, then this morning did the same, then got a bad electronics smell and now in pronterface I have a reading of over 1000 degrees as soon as I connect! Can only assume (after reading the troubleshooting) that I has a short on the connectors. I have a resistance of around 130k ohms on the thermistor, my fan still works when I hook it up to a battery and I have no continuity where I shouldn't have.

I switched over the bed and heater cables and my head is read as 20 degrees (but as the bed).

Uploaded the firmware still got issues.

I think I have done everything I can minus buy a new board! Don't fancy trying to re solder a chip onto it...

Anyway...any suggestions? Or is it dead

Cheers!

Ed

I edited pins.h and now have the hot end working via the bed screw terminals, so I have an extruder but no heated bed.

I red a thread on here that said I can 'make a thermistor circuit' and plug it into the header on the board. will look into that - not sure how one would begin to make a thermistor circuit...

If by bad luck you burned the pin where originally the hotend thermistor (or basically any other input or output) you do not necessarily have to replace the board. There are a few more pins available on the extension header. One might be already used to command the heated bed, but there are others available as well.
If you are sure about the fault, and you know what you are doing, then you have to:
- redefine the hotend thermistor pin in pins.h; you must use one of the analogue pins A1-A4
- build a circuit like the one you find on the bottom-left of the schematic of Melzi (http://reprap.org/mediawiki/images/7/7d/Melzi-circuit.png) - the one with ENDTEMP (or BEDTEMP, are the same); you may use a small protoboard to mount the resistor and the capacitor
- use a pair of wires and a 2-pin header to connect to the extension header (check the voltage on the right-most pins of the header for polarity)
- connect (or solder) the wires coming from the thermistor to ENDTEMP and ground on your board
- connect one wire from the ENDTEMP on your small board to the pin on the extension header corresponding to the one you configured
Be sure to remove any defective component or shortcircuit.
Wish you good luck!