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Old 17th May 2021, 6:09 pm   #33
factory
Heptode
 
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 898
Default Re: HP 180A Oscilloscope.

Quote:
Originally Posted by dave cox View Post
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
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