OC44 - leads corroded away - flux or batteries? - UK Vintage Radio Repair and Restoration Discussion Forum

6SN7WGTB · 16th Sep 2022, 7:49 pm

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?

Bazz4CQJ · 16th Sep 2022, 8:14 pm

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

Radio Wrangler · 16th Sep 2022, 8:29 pm

Perhaps an acid flux and a lack of cleaning, but there looks to be patches of rosin around some pins.

David

Philips210 · 16th Sep 2022, 9:01 pm

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

John_BS · 16th Sep 2022, 9:09 pm

Quote:

Just looking at an old piece of test kit which has OC44s.

Are you in need of some replacement OC44's?

John

paulsherwin · 16th Sep 2022, 10:17 pm

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.

6SN7WGTB · 17th Sep 2022, 8:22 am

Quote:

Originally Posted by Philips210

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.

Regards,
Symon

That looks to be a probable answer as the leads appear to have delaminated in layers

6SN7WGTB · 17th Sep 2022, 8:58 am

Quote:

Originally Posted by John_BS

Quote:

Just looking at an old piece of test kit which has OC44s.

Are you in need of some replacement OC44's?

John

Thanks John - you have a PM.

Craig Sawyers · 17th Sep 2022, 9:10 am

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

6SN7WGTB · 17th Sep 2022, 9:25 am

Yes agree, it has all be heavily 'got at'. And badly.

Heatercathodeshort · 17th Sep 2022, 11:15 am

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.

Refugee · 17th Sep 2022, 11:41 am

Quote:

Originally Posted by Craig Sawyers

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

There is also a blue thru hole capacitor next to the emitter of the lower transistor with corrosion next to where the transistor has been soldered.
I suspect that it has been repaired with plumbing solder and may have lasted for some time before the flux caused the corrosion.

AC/HL · 17th Sep 2022, 3:40 pm

Some early transistors used iron leads for the hermetic seal. These can now be very fragile if bending near the seal.

emeritus · 17th Sep 2022, 8:52 pm

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.

16th Sep 2022, 7:49 pm	#1
6SN7WGTB Hexode Join Date: Apr 2021 Location: Crawley, West Sussex, UK. Posts: 442	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? Attached Thumbnails

16th Sep 2022, 8:14 pm	#2
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,934	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 __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.

16th Sep 2022, 8:29 pm	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,869	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 __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

16th Sep 2022, 9:01 pm	#4
Philips210 Nonode Join Date: May 2007 Location: Redruth, Cornwall, UK. Posts: 2,573	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, 10:17 pm	#6
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,943	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.

17th Sep 2022, 9:10 am	#9
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,982	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 __________________ Doomed for a certain term to walk the night

17th Sep 2022, 9:25 am	#10
6SN7WGTB Hexode Join Date: Apr 2021 Location: Crawley, West Sussex, UK. Posts: 442	Re: OC44 - leads corroded away - flux or batteries? Yes agree, it has all be heavily 'got at'. And badly.

17th Sep 2022, 11:15 am	#11
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	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.

17th Sep 2022, 3:40 pm	#13
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	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.

17th Sep 2022, 8:52 pm	#14
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,339	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.