Re: PSU tolerances


Colin Eby
 

Hi JB, 

Evaluating caps is an early activity for most of us.  I was more trying to find guidance about the specific importance of voltage to system longevity. This was triggered by my local supply being particularly hot.  

Of course capacitor evaluation and replacement is always a step in system maintenance/restoration.  The project that triggered my query is following Ansgar's excellent guidance here: https://www.hp9845.net/9845/tutorials/preparations/. As recommended, I've completely replaced all the RIFAs in the PSU.  I also had to replace the line filter which is a sealed unit.  Three minutes on my local supply after a lifetime spent on 110v in the US, and the magic smoke came roiling out.

My own experience with electrolytics is that unless they are modern (5-20 years), or obviously faulty, don't mess with them before being given a specific reason to.  They tend to reform with use, and the larger they are the longer they appear to live. In any case, I don't usually replace those pre-emptively.

I know tantalums can be an issue, but I've not heard any pre-emptive replacement advice for this particularly machine on this forum (I'm working on a 9845B/T).

What's more worrying, is other high stress components -- for instance, in the crow bar circuit, and regulators.  They are much less obvious when they degrade.  If turning the heat down keeps them going a bit longer, then that would be interesting to know, wouldn't it? 

King regards, 
Colin

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