PIC32-HMZ144 board simple fault?

[PeterG]

Sorry if this is the wrong place to ask
I recently bought two PIC32-HMZ144 boards directly from Olimex.
I've noted published revision of the clock circuit - these are both Rev B with 12MHz crystal. It does look like these boards were modified in the crystal circuit after production.
I programmed the Blinking LED example onto them.
I have powered the boards via EXT using 5V as instructed in the manual.
One board is fine, the LED blinks ok.
The other board runs only intermittently, sometimes it ignores RESET and sometimes fails to run on power-up. (It was also reluctant to program, had to try a few times before it connected to Olimex PICKIT3 ok). The 3.3V rail is ok I checked it. When this board does run, the yellow LED is strangely very much fainter than it is on the first board! The yellow LED resistor has the correct value. The POWER LED lights just as brightly as it does on the first board.
Please does anyone recognise this fault and please have any ideas how I might fix it?
It is hardly worthwhile returning the board to Olimex due to postage costs. I just hope anyone knows this fault to save this board from being wasted. I have an oscilloscope and some experience in electronics.
Thank you
Peter G

[JohnS]

I'd email their support with a link to the post in case they do not notice it soon.

John

[kyrk.5]

Make some measurements with the ossci to see if there are any differences seen betwen the two boards. Of course flash the same SW, and try to measure Power Supply, Reset, osscilator pins. Maybe there will be some difference that can help to localize the problem.

[PeterG]

Thank you both. Olimex have replied helpfully via their support Email address, with a similar reply - I admit I've been a bit dim about this and I should check a few more signals and especially by comparing the boards running identical code. Thank you. p.s. sorry Olimex it is of course a green LED.