Cisco 7821 has a blank screen

[chumphol homsuwan]

Cisco 7821 has a blank screen as shown in attached file.

What I have tested so far:

1) Upgrade phone firmware to 10.3,11.5,11.7.12.5

2) Pull good working lcd from good unit to replace bad unit phone

3) Ip Phone can register to CUCM 11.5 as normal

None of these can resolve the problem

[Chris Deren]

If phone registers and working LCD still does not work on it, then seems like the issue is on the circuit board.  You could try to troubleshoot it with multimeter, but there may not be a quick fix to it.  Also, not sure it's worth your time as I see 7821s on eBay for $20-70.