Kikusui COM7101A Oscilloscope - Horizontal final amplifier bad

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Hello community,

I am stuck trying to repair this older scope from the 90ties. It is an analog scope, with a digital storage part. The horizontal system stopped working. The final amplifier is a hybrid (H31 in the schematics) that is mounted together with some external components on the horizontal/vertical amplifier PCB. I was able to remove most of the resin from the hybrid and it contains an h-bridge that drives the CRT horizontal plates with 140V. Several resistors were out of spec and a 330 Ohms resistor was burnt. I replaced them and the 330 Ohms burns immediately when I connect the 140V to the module. I am running in circles when I try to understand why, but it measures 140V on one side and 5V on the other. It seems like the wrong transistors of the h-bridge are open and connect the resistor to the 5V rail. All transistors on the hybrid seem okay (diode tester). All resistors are within 10%. Looking at the input pins 10 and 11 (where the signal comes from the motherboard) I can see a lot of spikes where I would expect a clean sawtooth. These spikes are still there when I pull the amplifier pcb, so they come from the motherboard. I am no longer sure whether the issue is the hybrid, or whether these spikes cause the problem. Sorry for my English and the baby oscilloscope that I use to troubleshoot the other one. -- AIso, I desoldered the 4 h-bridge transistors and tested them externally. They are okay.

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Fixed!
The spikes were caused by the character generator when it deflects the electron beam to write characters on the screen. I am not 100% sure what the problem was, but removing one of the feeding resistors for the h-bridge from the hybrid and using an external resistor instead did the trick. Happy to have this old scope back!