Before i bin it,

I got a nearly new Garmin 540s sounder with external gps with my boat, as i didn't want it i pulled it out and put in a a ray. Thought i would check it before i put in in another boat went to power it up starts off perfectly at full brightness and after 2 seconds drops to max dimmed (everything else works perfectly ). No matter what i do ( Factory reset with software + Firmware upgrade ) put the unit on full brightness it just stays dim. ? But works at full brightness every time i power it up. Have spoken to garmin no answers.

Just a stab in the dark but any ideas ?

Cheers

Vinnie