The Backlight In My Lcd Has Stopped Working. What's Wrong - Icom IC-746 Faq

The above chart is available on the WWW at:
http://groups.yahoo.com/group/IC746/files/IC746-Power.jpg
6.7

The backlight in my LCD has stopped working. What's wrong?

Short Answer
Your problem is probably one of the display driver transistors on the S-Logic board behind
the display. It will have to be replaced.
There is reason to believe (but no proof) that setting the LCD brightness to HIGH may
reduce the failure rate.
Long Answer
Unfortunately, this has become a problem for many 746 rigs, as evidenced by the data
collected at:
http://groups.yahoo.com/group/IC746/database?method=reportRows&tbl=2
It's not the actual 'lamp' itself, but one of the driver transistors. The lamp is fluorescent, and
will probably never wear out. Even if it did, the lamp isn't available as a separate part; it's
part of an assembly you need to get from Icom.
Background into problem
There is a DC/AC converter driving the "lamp". Check the S-Logic board for transistors
Q301, Q302, Q303, and Q304. Q302 is usually the culprit as it is the voltage/current
regulator for the dimmer function. If you have a DC voltage on the collector, which is
IC-746 FAQ
Page 70 of 113
2003-02-08