Quote Originally Posted by cropwell View Post
Any ideas what I could test, bearing in mind that this fault only shows itself after a few minutes printing ?
It's a bugger.

So, it used to work, but is now intermittent? So something has changed.

Thoughts:

Dry-joint and thermal expansion causing the joint to break when the microcontroller starts to warm up. Reasonably possible - examine the SMD device under magnification; if you're handy with an iron (and have a reasonable good iron) then a splash of flux across the SMD pins and walk a ball of solder over the pins and clean-up with desolder wick/braid then clean the board with IPA etc.

or...

Another person had a problem with a failed crystal - a 16Mhz crystal costs pennies and is a 10 minute job to replace. It could be that it's failing under vibration of the printing.

or...

Power Supply failure?, might be worth scoping/triggering on the supply level dipping a bit. More unlikely than the above, and would need a scope to fault-find. Could be caused by a faulty stepper driver drawing too much current.

(that's a thought - can you drive each axis to see if any one is causing problems?)

Have a look at the caps around the switched-mode PSU - any sign of leakage or bulging - worth replacing (you could be getting spikes on the logic supply).

Other noise?, that micro is likely all configured for I/O with only the supply lines and reset lines likely to cause problems.

Actually, could you swap the drivers around?, see if the problem follows a driver?

You mention conductive crap... possible, and there's nothing wrong with a bit of compressed air (just don't poke it down the buzzer). But definitely worth an inspection under magnification.

AvE (youtube) has a plausible theory that thermal issues account for the majority of problems - have a poke around with a finger whilst the printer is running - anything getting hot?

Basically... lots of things to look at and definitely worth spending 30 minutes really going over the board.It's a low density board, quite workable, but much depends on your dedication to not spending money (I'd have a bloody good go at it before forking out £150)