[Andrewausfa]

I picked up this 1976 era 15 MHz 'scope at a rally recently as it semed in excellent condition, especially after a little cleaning and has several features my more modern 'scopes don't have. However, it has a really annoying fault that I wonder if anyone else may have experience of.

The issue is intermittent triggering. When powered the triggered sweep may decide to a) start halfway across the screen, b) in the correct position and then fade or c) work as advertised. Or not at all. Hmmm. When it does work all functions seem to work correctly.

With zero experience of working on 'scopes, my first thought was to carefully clean all the switching contacts where I could and to press or twist all the knobs and buttons lots of times. I also carefully removed and reseated the transistors bar the FETs. I noticed one electrolytic (C421) was bulging and had leaked so replaced that, switched back on expecting an instant fix but nope, it was the same.

Having got really annoyed with it a few days ago I gave the Trigger Level knob a good flick with my finger and that brought the sweep to life. A-ha! I thought, dodgy connection. I've had a prod and tap around the sweep/trigger board (pic below) components with no luck but however I found that by exerting a slight pressure on the board around where the brown variable resistor is, the 'scope works perfectly. Not keen on removing the board but would opinion suggest this might be a dry joint, cracked track or another known fault?

Thanks - Andrew