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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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16th Sep 2022, 7:49 pm | #1 |
Hexode
Join Date: Apr 2021
Location: Crawley, West Sussex, UK.
Posts: 443
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OC44 - leads corroded away - flux or batteries?
Just looking at an old piece of test kit which has OC44s.
The leads of all are severely corroded, some to the point of having broken. The unit doesn't show obvious signs of battery leakage, so is this a consequence of the venting of very old zinc carbon batteries (such as gives a light grey coating to metal in old battery radio sets) , or is it corrosive flux that seems only to go for the leads of the OC44s? |
16th Sep 2022, 8:14 pm | #2 |
Dekatron
Join Date: Apr 2009
Location: Oxfordshire, UK.
Posts: 4,935
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Re: OC44 - leads corroded away - flux or batteries?
It's notable that the OC44's are in a far worse state than anything else.
Maybe the person who installed just those components had a packet of salted crisps for lunch and didn't wash their hand afterwards. Such things did happen! B
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16th Sep 2022, 8:29 pm | #3 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,876
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Re: OC44 - leads corroded away - flux or batteries?
Perhaps an acid flux and a lack of cleaning, but there looks to be patches of rosin around some pins.
David
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16th Sep 2022, 9:01 pm | #4 |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,573
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Re: OC44 - leads corroded away - flux or batteries?
I've come across similar corrosion in various old test equipment. I would imagine it's due to some outgassing from batteries coupled with high humidity to speed things up.
I sometimes wonder if old PVC wiring that degrades will contribute to causing corrosion of surrounding components. It's known to rot the conductors in the wire producing a green goo. Also, some component leads aren't tinned copper but instead have a steel core so that may account for the excessive corrosion on the OC44's leadouts. I guess it really all depends on the nature of the corrosive atmosphere be it acid or alkaline. Leaking electrolytic caps won't help either but would normally leave residues on the board but outgassing could contribute to localised corrosion. Maybe there is an acrid smell in the equipment to give a clue? I wonder if the print side of the PCB is showing signs of corrosion? It's an interesting challenge trying to find the answer. Regards, Symon |
16th Sep 2022, 9:09 pm | #5 | |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,780
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Re: OC44 - leads corroded away - flux or batteries?
Quote:
Are you in need of some replacement OC44's? John |
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16th Sep 2022, 10:17 pm | #6 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,947
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Re: OC44 - leads corroded away - flux or batteries?
Occasionally OC series transistors do develop rotting leads if the item has been poorly stored. I once had a TR82 where the OC71 leads had rotted.
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17th Sep 2022, 8:22 am | #7 |
Hexode
Join Date: Apr 2021
Location: Crawley, West Sussex, UK.
Posts: 443
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Re: OC44 - leads corroded away - flux or batteries?
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17th Sep 2022, 8:58 am | #8 |
Hexode
Join Date: Apr 2021
Location: Crawley, West Sussex, UK.
Posts: 443
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Re: OC44 - leads corroded away - flux or batteries?
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17th Sep 2022, 9:10 am | #9 |
Dekatron
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,984
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Re: OC44 - leads corroded away - flux or batteries?
From the appearance of the solder joints, those OC44's have either been replaced or leads desoldered to test them and then resoldered.
Compare the joint to the capacitor soldered to a similar pin. Craig
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17th Sep 2022, 9:25 am | #10 |
Hexode
Join Date: Apr 2021
Location: Crawley, West Sussex, UK.
Posts: 443
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Re: OC44 - leads corroded away - flux or batteries?
Yes agree, it has all be heavily 'got at'. And badly.
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17th Sep 2022, 11:15 am | #11 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
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Re: OC44 - leads corroded away - flux or batteries?
We all thought transistors would last forever. Recently many have failed and a lot will follow. Lock-fit and many other types appear to suffer from capillary dampness/rust breaking down the glass/Bakelite joint. This is probably or will be the cause of I/C failures. The old vacuum valve has had the last laugh! John.
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17th Sep 2022, 11:41 am | #12 | |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,553
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Re: OC44 - leads corroded away - flux or batteries?
Quote:
I suspect that it has been repaired with plumbing solder and may have lasted for some time before the flux caused the corrosion. |
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17th Sep 2022, 3:40 pm | #13 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,642
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Re: OC44 - leads corroded away - flux or batteries?
Some early transistors used iron leads for the hermetic seal. These can now be very fragile if bending near the seal.
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17th Sep 2022, 8:52 pm | #14 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,339
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Re: OC44 - leads corroded away - flux or batteries?
The gases emanating from PVC can certainly cause problems if used in hermetically-sealed equipment, which was why PTFE-insulated wire was used in sealed units in my time at Plessey. We were told of an item that had come in for modification where the technician had used PVC wire instead of the specified PTFE. When the unit was subsequently returned as faulty, it was found that the polystyrene capicitors were dissolving.
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