Reinhard Loose

Hello,
I got an old not working 2430. After replacement of some burned capacitors it worked fine for more than 5 years.
Now, after power on I get a scrambled/garbage screen which is variable from power on to power on (see 2 images).
The LEDs (Trig'd, Ready, Arm, +, -)  are dead and don't even flash at power on. The three GPIB status LEDs  are on.
All front panel buttons and controls are dead.
Is there any idea where in the trouble searching procedures or in the schematic diagrams I should seek?
I have the complete service manual.