[Solved] Programming Mega2560 with Uno: Device signature = 0x000000

I've read through several threads here and elsewhere on this subject however most of them seem to be solved by 'it suddenly started working' so I was not able to really apply anything to my situation.

Currently I am attempting to upload the blink sketch to an arduinoMega using an uno as a programmer. I am attempting this in preparation for a self made board that will be using a stand alone Mega2560 chip and 16MHz crystal. If possible I would like to perform all programming operations via the 6pin header (MISO,MOSI,RESET,etc). From what I have read this should be possible.

At the moment I am able to load a sketch directly into each the uno and mega boards via the arduino IDE. so I know both are working boards with bootloaders. I've trippled checked the wiring between the uno's pins 10,11,12,13,+5,GND to the Mega's programming header as well as the physical pins on the chip and edge of the board.

Additionally I am using an external 5V supply as suggested elsewhere on the target board. However I am still getting: avrdude: Device signature = 0x000000. This is being attempted by using the 'upload using programmer with the following settings: Board: ArduinoMega2560 Processor: Mega2560 Com Port: Uno (loaded with ArduinoISP sketch) Programmer: Arduino as ISP

I have also read into changing the boards.txt file. I have attempted this as well using Notepad++ but did not see a difference either way. I assume this is just for setting the bootloader, which I have not actually done since this is a working Mega board which I can still load sketches directly into.

Is there anything else I could be missing here? I will be attempting this on another computer as well just in case my IDE is acting up.

Edit - A fresh install of the IDE on a different PC produced the same results, programmable directly but not via the Uno.

Double check Pin 10 continuity, on the Uno to Reset on the Mega. Power Leds bright, both units?

Yep, both powered on and brightly lit. I had checked each of the pins about 20times since I was sure that's where my issue was.

I am using a 6 pin cable with pin 5 (Reset) cut out and extended to plug into Pin 10 of the Arduino used as an ISP. Today I had a Mega not clearly marked for Pin1 and reversed my plug. Leds were brightly lit, I thought, but nothing would load. Then when I figured out I had made a a mistake, the capacitor between Reset and gnd on the Arduino used as a Programmer caught me also.

Some days I think everybody would be a lot better off, if they bought two Usbasp's and upgraded the firmware to 1.06 Alpha. Anyway, remember if you get a sketch to upload, it wipes out your bootloader which will cause you grief when you try to load a sketch the normal way. :)

In the end the bootloader wont matter as this is just going onto a standalone chip. I did, however, get my pcb in yesterday and got it populated ...it worked just fine there, so not sure what the issue with the Mega board is. I am still able to upload to it directly so no indication it's bad.