Products > Test Equipment

HP 8656A nauseating smell

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tverbeure:
Ok. That’s the current plan then: carefully label all the wires, remove the old filter, and find something else without the filter.

Worst case, it doesn’t work, but the smell is just too unhealthy. I’m moving the opened up generator to a cold garage because it’s polluting the air of my cave too much.

Edit: I removed the Corcom filter and took it too a different room. It doesn't smell at all. Which means that it's some other component that's the culprit, maybe the the A14 filter bank assembly. :(

Swainster:
I think the A14 filter assembly is just something that looks like a D-sub connector, and is probably just a bunch of ceramics caps potted inside the D-sub shell - not a lot to go wrong. The electrolytics are on the big board that you see when you take the bottom cover off the unit - these are more likely to be responsible for emitting smells. On second thoughts, tantalum beads could be the prime suspect after RIFAs and before electrolytics, for an instument of this age.

On a related note, at least to my nose, RIFAs are the ones which smell like crystallized body odour, whereas the last electrolytic failure that I came across was more like a fishy/rubbery smell, which slowly developed over time. I've also smelled a vinegary smell from leaking "new old stock" electrolytics. I dont recall what the last tant failure smelled of as they usually let go with a pop or hiss, and visible smoke, which tends to distract from the smell (as least it distracts me while I frantically grope for the off button).

tverbeure:
You're right. A14 was a dud. I took apart the complete rear assembly for naught: nothing smelly. I hope that I manage to put everything together again!

I'm now convinced that the large caps are the biggest contributors. I've removed them, put my nose against them, and my throat is still burning...

The plan is now to remove all larger caps on the A10 power supply board. Someone on Twitter suggested giving the board a deep clean with flux removal aerosol, which I'll do. The prices for replacement caps on Digikey are very high ($20 for the 23000uF replacement) if you select axial types, but those prices drop to something like $3 for standard types, and much cheaper for lower capacities. I'll be done a bunch of soldering to get wires attached...

Tom

tverbeure:
The Agilent-provided operating and service manual of the 8656A has the schematics, but they're all split over multiple pages.

I've cut-and-pasted them all together and created a PDF file with just the schematics. You can find them here: https://tomverbeure.github.io/2024/02/22/HP-8656A-Schematics.html.

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