power circuit in your ST-60 is fried. Just had this problem a couple of weeks ago. Do a Google
search for "ST-60 Instuments Manual". There's a .PDF file out there that you can download and will walk you through the troubleshooting and repair
...great document! If you are technically proficient at soldering electronic components you may be able to repair
it yourself since ST-60's are no longer supported by Raymarine
. The alternative is to upgrade to the i70 Raymarine MFD if your system supports Ng Seatalk
or higher...Pricey though. Was able to repair our ST-60 but the owner went ahead and bought an i70...now installed as a remote
in his cabin
. Nice piece of kit I have to admit, and I don't care for Raymarine stuff usually.