HP 8656A nauseating smell

[tverbeure]

I bought this HP 8656A for very cheap at electronics flea market. Apart from a "power" button that's a bit cranky (but working if you finesse it right) and output power levels that can't be trusted, it's working reasonably well.

But it's unusable due to the nauseating smell that it generates as soon as it powers on.

I've heard about RIFA smell, but I don't see anything that reassembles RIFA capacitors on the power board.

Has anyone had similar issues, or has anyone recapped some of the capacitors on this type?

[Swainster]

I seem to recall that the RIFAs are hidden inside the schaffner inlet/voltage selector assembly on the 'B' version - maybe it's the same on the 'A' ?

[Swainster]

I think this is the inlet filter for the 'A' version https://www.ebay.com/itm/385395000014. Sadly, any RIFAs (if that is what is used in this filter) are also going to be pretty old by now.

[DavidAlfa]

Some electrolytics can also get pretty bad, some smell like a sweaty groin after 3-day non-stop party!

[tverbeure]

I seem to recall that the RIFAs are hidden inside the schaffner inlet/voltage selector assembly on the 'B' version - maybe it's the same on the 'A' ?

Aha! I saw that element after removing the backplate. It didn’t have a particularly foul smell though.

It’s tempting to do a bunch of fixes of filter and caps, the only issue is that I will quickly exceed the $80 that I paid for a unit that I don’t have a real need for (as if lack of need was ever a reason to not to buy test equipment…)

[tverbeure]

Some electrolytics can also get pretty bad, some smell like a sweaty groin after 3-day non-stop party!

The smell is truly horrible and still stuck in my throat half a day later. Definitely not healthy and worse than socks!

[KE5FX]

Yeah, the 8656A stinks on ice....

Oh, you meant the RIFAs. 

[tverbeure]

Yeah, the 8656A stinks on ice....

Oh, you meant the RIFAs. 

I’m experimenting with phase noise measurements and my R&S SMHU is just too good!

[tverbeure]

I think this is the inlet filter for the 'A' version https://www.ebay.com/itm/385395000014. Sadly, any RIFAs (if that is what is used in this filter) are also going to be pretty old by now.

The 8656A uses a component 0960-0442, a Corcom F2058. There's still a few available on eBay, but they're all used, so chances are those RIFAs will be broken just the same. The HP 8656b service manuals shows a 0960-0679, but I can't find the actual component for that. But both have 3 main pins (ground, L, N) and 7 voltage selector pins A-F,J but with some differences (Pin C is double on the 8656A but not on the 8656B.

In your 8656B repair, you're using Schaffner FN370-2-22. Is that one pin compatible with the 0960-0679 or did it require some amount creativity to make things work? What about the mechanicals?

Bonus question: how does one even remove that Corcom F2058? It has these 2 plate metal wings on either side, but so far I haven't figured out yet to dislodge the thing.

[Swainster]

0960-0442 is just the HP internal part number for the Schaffner FN370 filter, so it's an exact replacement - amazingly still stocked by 'Mouserkey'. Unfortunately it doesn't look anything like the filter on the 'A' version so would probably quite difficult to retrofit. It's also quite expensive, so if you are going to make a substitution, there are definitely cheaper options out there (though you would probably have to hardwire the line voltage selection)

[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.