Tektronics 2225 Faulty Trigger Circuit

[woood777fly]

Good Evening I have a tektronix 2225 oscilloscope that I have not used for a number of years. I needed it to measure the output from a 26mhz Xtal oscillator but I cannot see a sensible waveform. It just looks like a blurr. The waveform from the 1khz test point can be held still with a little fine tuning on the 'hold off' pot but any higher frequency cannot be displayed properly. The trigger LED only comes on briefly on the 1khz test point when I slide the 'mode' switch from one side to the other, on higher frequency the trigger LED does no come on at all. Does anyone have any ideas on where to look on the pc board for the trigger fault. I have a copy of the workshop manual but dont know where to start looking. The circuit boards are in lovely condition no corrosion and no obvious burned tracks although at the moment I cannot see the front board without taking the front plastic panel off the scope. Kind Regards

[jdragoset]

The detailed trigger schematic is schematic "diamond 3", as shown on the block diagram.
First try to exhaust all front panel possibilities, try external trigger in, etc. to verify no trigger signal under any conditions.
Also check for front panel for LF/HF trigger reject.