Quote:
Originally Posted by dave cox
The foam is there to improve electrical isolation. This is probably more of an electrical breakdown than an overheat, maybe a crack in the capacitor casing and has 'arced' through the foam. Maybe when it was assembled there was too much pressure in that region - maybe 
Fingers crossed, replacing those two parts should bring you closer to a working scope.
When you replace the HV cap, be sure to carefully clean the surroundings with alcohol - especially anything that appears to have blackened. Carbon / soot is very conductive! Remove the existing foam, it should be replaced but I'm at a loss for a replacement at the moment, maybe Andy (DA) or David (factory) knows of something that could be used ...
BTW, it was very good that you followed your nose!
dc |
Looks to be a sheet of clear plastic under the foam,
hp used that nasty foam where parts/boards are liable to move with vibration or for isolation from vibration. It also tends to absorb moisture and corrode PCB traces & parts it's in contact with as a result, being 50+ years old it's often found crumbled everywhere inside some test gear, having been distributed by the cooling fan,
note: this scope doesn't have a fan.
David