Tektronix TDS 310 won't boot

[powder-phun]

About a year ago it worked perfectly fine. Then it spent about a year on a shelf in a magazine somewhere and now it won't boot. When i press the power button, the fan starts up, I can hear the relays, and all the LEDs on the front light up, but that's all. They never turn off, the screen stays blank. The official service manual states, that this is a problem with the main board, or the cable connecting it to the front panel.
http://www.mdc.umn.edu/facility/files/electrical/Elec%20Manuals/Tektronix%20TDS%20320%20Two%20Channel%20Oscilloscope.pdf
(page 131)
Sadly, the cable is 100% working, so the problem has to be with the main board. There are no visual signs of anything burned or broken off, all the voltages are correct. Do you have any idea what should i check next? Could the dallas DS1630AB-120 be at fault? I've heard that Tektronix had a big problem with SMT electrolytics at the time, but i can't see any.

Photo of the main board:
https://drive.google.com/open?id=0B4MInAcJQ5DbQXhVTDEzQmVpcjA

[PA0PBZ]

It looks like there is some moisture damage at the right side of U705 (ADG250B).

[powder-phun]

Yes, there was some gunk, which i  cleaned off (didn't help). Strangely, there is also no calibration signal, so most probably the front panel processor isn't working. I've checked it's supply voltage and the clock signal, both seem ok.