This probably sounds silly, but put the ETD board against a bright light – I used a 100W incandescent - component side towards you and solder side towards the light so you can see (sorta) through the PCB.
One of my ETD’s had a solder bridge between pin 1 and pin 2 on the PIC (and a pair of other PIC pins) and with the light shining through, I could see the ever-so-tiny bridges! (Believe it or not, I inspected every pin over and over with a fairly powerful magnifying glass and a microscope and I still missed the bridge!)
A little flux, a little solder wick and whoosh, the bridges were gone! ETD works perfectly now!

joe