OK. One last thing before I admit (temporary) defeat. You are not applying any power to your PCB I mean the only Vcc and GND going to your PCB when you try to program it is coming from the Pro Mini - right?

Right. No additional power - just the ISP header from the Mini

 

Right. No additional power - just the ISP header from the Mini

When the Pro mini is connected, do you see Vcc on your PCB ATMEGA pins 4, 6 and 18?

 

In order for your board to program from the Mini, you need to have Vcc and GND on certain pins on the ATMEGA on the PCB.


As far as I can tell (and I could be old, tired and wrong You need 5V from the MINI to the RED points, GND to the Green and the SS/Reset line needs to be at Blue.

 

I will check that with my multimeter and report back in a few hours

 

I will check that with my multimeter and report back in a few hours

OK, I may be done for the night, but I will check back. It took a while but it looks like you are trying to program the ATMEGA without power. The good news is that the board may work fine, but only after the ATMEGA is programmed. Please do let us know what happens?

 

Tested all the pads/pins for a short - everything seems ok. On each board I soldered only the barebone components (2x 22uF, 1x100nF caps, 10k resistor, XTAL) to test it. I can often see tiny sparks between the pins when I trying to flash the chip - but I cant find any shots

Make sure your xtal caps are pico, not micro.

 

Tested all the pads/pins for a short - everything seems ok. On each board I soldered only the barebone components (2x 22uF, 1x100nF caps, 10k resistor, XTAL) to test it. I can often see tiny sparks between the pins when I trying to flash the chip - but I cant find any shots

Make sure your xtal caps are pico, not micro.

What do you mean by that exactly?

EDIT: got it. Its late and my brain stopped working Yes, they are pico

 

Okay! I started fresh today. New PCB, new ATmega AND a new USBtinyISP adapter. Cleaned everything after soldering and checked for shorts. Viola -flashing was no problem!!! Well, not quite - it only works if I solder the RESET wire from the USBAdapter directly on the 10k resistor - not through the JST-SH pin header (C2 bridged). But I am pretty happy right now

 

Good Deal!

 

Good Deal!

Thank you for your patience and help!