Maxon CM 70 (urgent help)

I have 1 month old CB radio Maxon CM 70 and in last 2 week  I have strange problem suddenly radio lost all signal in receive and in output, S-meter don’t show anything, After some time I discover what causes problem in my CB radio.
I have for test purpose 6 days work with low (L) back light and everything work just fine, after 6 days I switch back light from L (low) to H (high) and the same error appeared again.
Then I turn-off and on CB several time and I manage to turn back light to L (low) and again CB work all just fine.
To be 100% sure I repeat the same step twice and I manage to get the same error again, so problem is when I in Mode choose H (high) back light.
Also, I have  re-solder all parts in VCO mode, so I don’t believe that problem is in VCO mode but who knows.
Can you please be kind and and give me some direction where to look for potential problem, or can you ask someone who have the same rig or have knowledge about this rig so I can be directed where to look for potential problem.
Please, any info I don't know where to look, I have also check all 4 transistors 2SB1367x2, driver and power all are OK, I don't know where to look, is it maybe processor?
Please, contact me on mail: max328ct001(monkey)yahoo.com