Harsh smell in HP device from 1976

[pcravero]

Hello everyone.

I am working on an HP device labelled 9403A, part of an HP 9550 "automated calibration system". The whole thing was in use between 1973 (first appearance in HP magazines) and 1976 (datecodes in my device). However I own only the HP 9403A (pictures on my blog at ik1zyw.blogspot.com ).

This is my first vintage HP test gear. It is almost sealed as it has no fans or air vents, so there is no air flow in any operating condition.

What puzzles me is that inside there is a harsh, rough smell that gets me in the throat. I have never smelled something like that. Sniffing around it seems to come from the bunches of wires routed around the large chassis rather than PCBs. The device works properly and there are no signs of leaks whatsoever. Also the smell is independent from off/on position, and it does not increase during/after operation.

I am looking for clues of what could be generating the smell and potentially how dangerous it is. After a session of a couple of hours I got headache and dizziness, but it could be caused by neck pain/rigidity.

Nevertheless I managed to decipher the parallel control protocol for the device and I can light its nixies and buttons to my liking. Besides, any tech documentation on HP 9550 system would be more than welcome.

Thank you for reading,

Paolo

[high_vacuum_house]

Its not an expired RIFA capacitor in the mains filter circuitry is it? These are well known to expire with a nasty smell but otherwise the device carries on working. Look around the mains input and see if there is any filtering present.

Christopher Capener

[pcravero]

Thanks Christopher.
I will have a look around the AC input. I didn't take pictures of that area. There is also an optional power supply that is stored into its own box that I should check, then!

Paolo

[turretslug]

An expired (or slowly expiring, sometimes they go with quite a pop, sometimes just gently smoking away) RIFA capacitor certainly has a distinctive smell combining smouldering paper with burnt epoxy that hangs around and frequently it leaves a dark brown treacly mess in the vicinity. Could the equipment have been stored somewhere that gets particularly hot, like a loft or enclosed shed/warehouse (and I imagine that these places get hotter in Italy than damp old Britain!)- some wire insulation can deteriorate and release decomposition products (e.g. PVC wire can release HCl, which would smell sharp). Whilst old rubber wiring is famous for decomposing, going either brittle or gummy, I've sometimes encountered plastic wire insulation that did something similar. Come to think of it, some plastic-insulated mains flex of the era can have a weird smell.

[Philips210]

Originally Posted by turretslug

Come to think of it, some plastic-insulated mains flex of the era can have a weird smell.

Hi

Yes, the 3-core PVC mains lead on my Philips TVette has quite an offensive odour so ended up replacing it.

Regards
Symon.

[dave cox]

Any sign of corrosion ?

PVC cable will often out-gas HCl (hydrogen chloride) but usually its not enough to actually smell !

dc

[pcravero]

Hello.

Originally Posted by turretslug

Could the equipment have been stored somewhere that gets particularly hot, like a loft or enclosed shed/warehouse (and I imagine that these places get hotter in Italy than damp old Britain!)- some wire insulation can deteriorate and release decomposition products (e.g. PVC wire can release HCl, which would smell sharp). Whilst old rubber wiring is famous for decomposing, going either brittle or gummy, I've sometimes encountered plastic wire insulation that did something similar.

I acquired the device in June 2018 in Germany, from a German HAM, so I have no idea how it was stored. The visual inspection suggests that it was carefully stored (or thoroughly cleaned) because there is no dust or rust whatsoever inside or outside, not even in the almost hidden parts of push buttons!

I attach a picture of the AC input and a zoom on the capacitor. It looks ok.

There is lot of wiring, so it could be the aging of lots of PVC insulation. Touching wires leaves no traces on fingers. Nor the insulation breaks in a visual manner. When removed, PCBs alone do not smell.

Unfortunately there does not seem to be a DIY way to do odor analysis (but I'm checking with a friend working in the R&D or a large chemical corporation).

Having decoded the control protocol I had hoped to be done with working inside it. Unfortunately yesterday it didn't behave as expected and there could be something fried (from a pull-up resistor network to HP 1820 ICs). Hopefully not caused by failing insulation
in bundles of 20+ wires.

Paolo

[Radio Wrangler]

That's a ceramic RF suppressor capacitor, not one of the Rifa paper ones, so it's not likely to be the source of the bad small.

The next thing to go looking for is a damaged tantalum electrolytic capacitor. There could be such things on any of the boards. They too can produce a terrible smell. A good visual inspection is the first step.

David

[pcravero]

A short update for those that participated in this thread. I opened up the device again and decided to cut a 30 cm long sample of signal wire going to an unused connector. Some of those wires can be seen in the picture above, going to the card connector.

I let the sample sit in a sealed plastic bag for few minutes and then I poke my nose inside: smell!

So, the harsh smell comes from all those wires in there. Now I passed the sample to a friend that hopefully can do a professional lab analysis (as seen in movies, but for real in chem industry) and report back.

Paolo