I've got an Atari 400 (NTSC) which I purchased as non-working.
The symptom is the fairly common Green/Yellow screen on startup.
Things i've tried:
Swapped CPU board with known working board
Swapped RAM card with known working board
Purchased a 48k/ROM board from TF_HH on these forums to replace the RAM and ROMS (incase the roms are the issue)
Changed out all Capacitors on the power board along with the 10UF cap on the motherboard.
12V and 5V (A&B) all tested as good.
Oscillator on the board reads correctly 3.579MHZ
Tested with a Donkey Kong cart
Cleaned all connectors, re-seated all chips
None of these have changed the behaviour of the issue in any way.
Here is one wierd thing:
Tested clocks around the board as per Figure 5-1 in the Service Manual .. All clocks are right on the money EXCEPT pin 37 on the 6502 .. it reads 1.64MHZ .. both CPU cards read the same on this pin. I'm not sure if this is an issue, seems odd though .. the Service Manual says that it should read 1.140MHZ.
Anybody with any ideas? I've run out of em