Quick question guys.
Ive decided to go back and fix a couple of Mega 2560's that I damaged from shaky hands with test leads that shorted 5vdc to ground.
USB power runs both boards fine.
It's 5 volt regulator output that's an issue.
When I supply 9vdc to the Vin pin, I can track the 9vdc voltage to 5v regulator on pin#3. "NCP1117"
The output voltage on pins #2 and 4 read 2.7vdc only half the voltage that it should be. I've replaced the NCP1117 regulators just to make sure that they were not the issue, but I still get the 2.7vdc reading after replacing them.
I'm assuming one of the cap's in the power circuit got destroyed at this point.
Anyone ever seen this and have an idea which cap it might be?
Thanks
Don't know of hand whats going wrong but it's not the caps... The output of the NCP1117 is directly connected to the 5V rail. The same rail the USB seems to power just fine...
Thanks for replying Septillion
I tested the 5vdc regulators that I replaced and they are working fine. Something else in the circuit is causing the regulator to read half voltage. One thing I noticed is all the boards I'm referring to are just Mega 2560, not the 2560 rev3. I appears there's a difference in the 5vdc circuit. I'm not sure what I'm looking at on the schematic. Looks like two 5vdc regulators but one is adjustable and they have two different pin counts. I'm sure its not two regulators but not sure what to make of it.
Tell me what you think
Thanks again
Yeahhhh, now you found a weak point of Arduino... They're terrible at schematics! The two regulators are to show you can use a SOP-8 or a sot-223. But they don't make that clear on the schematics. And the second one is not a adjustable, they are just lazy. You can get the MC33269 in adjustable or fixed voltage variants. The fixed voltages versions don't have a ADJ-pin but a GND-pin on the same pin-number. It would have been clearer if they used a different symbol for that.
Okay, back to the problem. When connected to USB, what is the voltage at the output of the regulator (although it does nothing, the 5V should be there)?
And can you check (DMM beep mode) the output of the regulator is directly connected to the 5V of the Arduino (5V output header pin).
And when you test with 9V, is the USB connected?