Dried Out!!

[Peter Beeney]

Photo 1 First signs.

Photo 2 Lazy solder.

Photo 3 Nonstick!

Photo 4 A crash is conceived...

Very recently a colleague gave me a few of his second hand flat pack transmitter and receiver packs, which he though would be ok to use, simply because he is upgrading to higher capacity units. I assume he’s been using these on a regular basis.

These transmitter packs are blue shrink wrapped, with no information on them at all. I don’t know whether they are original equipment or not. I don’t even know if they are nicads or nimhs.

Taking a look at one today, the first thing I notice is that there is some corrosion starting, it’s clearly visible in the plug, photo 1. Not as bad as some that I’ve seen, and observe there is already a small speck of verdigris on the positive pin. It’s at least a re-wire before we do anything else, so I cut open the outer shrunk on plastic covering and gently tugged on the black wire to pull it clear. It immediately just literally fell off the tag. Photo 2 is the top view of the soldered connection, whilst photo 3 is the underside, just as it came off the tag; and 4 is the tag itself.

I would suggest this is a really classic example of the classic way of making a really classic dry joint. For a start, when the cells were nice and new and shiny and clean, the wire should have been passed through the hole and turned back on itself; then made sufficiently hot enough for the solder to instantly flow out smoothly all round and really stick to the wire and tag. Here it looks as though the iron passed about 2 inches above. With the wire being held 1 inch above! To add insult to injury, when I tried the positive end, the tag pulled straight off the cell, it was supposed to be a spot welded joint, as in photo 4, and then when I touched the tag, it broke in half !* But at least the solder stuck!

I don’t think any of this a related to the corrosion, it’s not established enough here; and it only ever attacks the copper wire, not the tin and lead solder. This was a dry joint right from the start. It’s quite amazing that it didn’t cause any odd glitches. Having said that, I’m only assuming that it didn’t. Together with the positive end woes, it can have only been hanging on by the skin of it’s teeth, as they say.

What is slightly disconcerting is the fact of knowing this could be in a a tx near you! Or even in a transmitter at a show. A popular pack configuration. I think it may very advisable to always buy any replacements at least with a brand name label on.
Not the first example of this, Chris Bashford of Mainlink Systems flagged one up in the BMFA News a long time ago. Just how many others are lucking about, and unless you cut the covering off, your’ll never know. Yet another good reason for changing to LiFe, at least there won’t be any corrosion, but that doesn’t always mean the soldering is always right on the job!

Fortunately I have seen very few warnings about this, so I’m sure it’s not a big problem; or even a little one, perhaps. I must admit, of the many batteries I’ve rewired I’ve not seen this before. The wire soldered joints are always secure, but sometimes the welded tags look a bit suspect, so I always give them a good tug, but invariably they are hanging on for dear life, too.

Sleep tight, don’t have nightmares……

PB

[TheFlyingCrust]

Hi Peter, When I was previously into RC some 25 years ago there were a number of discussions on black wire corrosion, nicknamed Black Wire Blues. It affected Nicad equipped kit, both Tx and Rx. I can't remember the the cause but there were articles in RCM&E at the time.

I have always been very vigilant since and when I resurrected my old 35MHz gear last year it wouldn't work. You should have seen the state of the -ve connectors and cabling. Its strange but there wasn't any sign of corrosion on the +ve side. It very rapidly found its way in the bin. Daren't risk using the gear. Now on 2.4Ghz (HiTec) but I still check the leads and connectors fairly regularly.

Ian