Varied output levels on Mega 2560 R3 Digital Outs????

Hi All-

Currently I'm working on building up a test board to validate my code before adding the external hardware. Basically, I am using switches and LED's to prove out my sketch and make sure events are happening (LED's are lighting) when expected. For the sake of simplicity, I won't get into the code, that is not where the issue is. (Dumbed it down to a simple sketch to output high on LED pins to make sure they are illuminating).

So here is what I am seeing: Pins 2-21 are all outputting as expected. Running LED's with a 220Ohm resistor, they illuminate nicely.

Then I get to testing my Outputs on the header of 22-53. This whole header seems to put out less. Depending on LED color, it either does not illuminate, or barely illumates. (I've checked the Same LED's on pins 2-21 - they work fine there). I checked the No load voltage, it's right at 5V. Under load, either 22-53 has a drop across the LED of 2.4V, while pins 2-21 show a drop of 3V across the same LED, with a 200 ohm in series. I can't seem to measure current, or I would report it. Should be easily calculated, though.

Anyone know what is going on? Do I have a faulty board?

All pins have the same drive strength on the m2560.

Are you remembering to set all the pins as outputs? If they're not set as outputs, writing them high will just turn on the pullup (so there's an extra ~30k resistor in series with the LED)