ATmega16 trouble shooting


This is my first post. I am fairly new to the world of MPU's and such and I am actually trying to trouble shoot a PCB I have with an ATmega16 au chip in it.

This board was functioning properly then stopped one day when I powered the board. When I say stopped I mean it acted as though there was no power to it. no led indicators, no displays, no relays, nothing.
I checked to ensure that the AT-mega16 was receiving the proper voltage at each of the VCC pins described on the data sheet, which it was. I checked all of the other powered components and they too seemed to be getting the proper voltages, and yet nothing was working.

I started to suspect that the crystal was bad on the XTAL1 and XTAL2 circuit because while I was checking for voltages I touched that circuit with the leads on my multimeter and for a split second the board would function, then shut down again. I assumed the crystal was bad so I replaced it.

After replacing the crystal in the oscillator circuit there was no change in the board. So, I temporarily jumpered across the legs of the crystal while the board was powered and the board started show signs of life again.

I see that these circuits typically have small capacitors between each leg of the crystal and the ground and I am assuming that is used to stabilize the signal, could these be the problem?

if anyone has a suggestion let me know, I don't really want to spend the $2000 on a new board if its something small I can replace at home.

I appreciate any advice you have. Thanks!

Show us a good schematic of your proposed circuit.
Show us a good image of your ‘actual’ wiring.
Give links to components.

Hi LarryD,

Thanks, I have uploaded a picture of the board. I don't have a schematic as this is a board from my Miller TIG welder and I cannot find one.

Please check the voltage on the controller’s power pins.

Also check the voltage on the reset pin.

All 4 of the VCC pins were showing 5vdc +-0.01vdc.

I will check the RESET pin voltage and get back to you.

The RESET pin should show 5vdc during operation, correct?

Hi LarryD,

Confirmed that the Reset pin is also showing 5vdc. I don't know where else to go from here. What do you think?

Check all the soldering, especially on SMD devices.

Look at the SMD resistors and examine for cracks in the ceramic substrate.

A magnifier goes a long way.

Using a ohm meter, confirm all switches work properly.

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