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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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7th Jan 2019, 4:43 pm | #1 |
Triode
Join Date: Aug 2009
Location: Torino, Italy
Posts: 47
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Harsh smell in HP device from 1976
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 |
7th Jan 2019, 4:51 pm | #2 |
Octode
Join Date: May 2003
Location: Belper Derbyshire
Posts: 1,936
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Re: Harsh smell in HP device from 1976
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
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7th Jan 2019, 5:09 pm | #3 |
Triode
Join Date: Aug 2009
Location: Torino, Italy
Posts: 47
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Re: Harsh smell in HP device from 1976
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 |
7th Jan 2019, 5:18 pm | #4 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,400
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Re: Harsh smell in HP device from 1976
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.
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7th Jan 2019, 5:30 pm | #5 |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,580
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Re: Harsh smell in HP device from 1976
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8th Jan 2019, 12:12 pm | #6 |
Nonode
Join Date: Jan 2009
Location: Bristol, UK.
Posts: 2,062
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Re: Harsh smell in HP device from 1976
Any sign of corrosion ?
PVC cable will often out-gas HCl (hydrogen chloride) but usually its not enough to actually smell ! dc |
8th Jan 2019, 12:25 pm | #7 | |
Triode
Join Date: Aug 2009
Location: Torino, Italy
Posts: 47
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Re: Harsh smell in HP device from 1976
Hello.
Quote:
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 Last edited by pcravero; 8th Jan 2019 at 12:42 pm. |
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8th Jan 2019, 2:07 pm | #8 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,902
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Re: Harsh smell in HP device from 1976
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
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16th Apr 2019, 4:08 pm | #9 |
Triode
Join Date: Aug 2009
Location: Torino, Italy
Posts: 47
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Re: Harsh smell in HP device from 1976
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 |