Hello Stojan
?
I have seen this issue before, where everything works normally at 12V but when the supply voltage is reduced, it stops working. I recall that it was due to a knocked off component on one of the SMPS. Most probably the 3.3V SMPS. Perhaps D105, right at the corner of the board? It's worth checking the SMPS visually to see if there are any faults like this.?
?
73 Hans G0UPL
http://qrp-labs.com
