Clansman 320 wiring fault.

[kernowcam]

I have a 320 to repair, signs of life and starting to work on it.

Last night I noticed the main power wire connected to the tag from the + battery post had dropped off. The tag is corroded as well.

Also the negative tag cluster were very loose.

What is the normal effect of a corroded but hanging on by a thread wire here?

I am wondering why this happened as the set is waterproof and has a silica gel insert in it.

[QQVO6/40]

I can think of a number or reasons for pan-climatic sealing failure.
The age of the set has a large influence on moisture content. As they age, the seals dry out, become hard, ( rubber "O" rings are supposed to be sort of soft and pliable and able to move and this is why they are lubricated) the majority of "O" rings have a round cross section but when they age they flatten and loose resilience. Military radio mechanics are quite often rushed to get a good turnover in the workshop and do not really take the care that is needed to keep seals perfect. The whole of the sealing surfaces must be clean of grit and dust or fibrous material.
It is generally accepted that once a set is opened up for service in a workshop that it is pressure tested before leaving said workshop. Sometimes this is done rather quickly and does not detect tiny leaks.
Another factor is the set's environment. If you have a radio that has been in a nice warm barracks for quite a while and then it is placed on a "grunt's" back and they are both thrown out into a heavy snow blizzard, then the seals on both of them are going to be very stressed. ("grunt" a term used to describe an infantryman. Derived from the sound they make when picking up and shouldering a very heavy pack.)
The Clansman range of radios were designed to withstand total immersion in water (less than 1 metre). Some of this water is rather salty when doing a beach landing. Refer previous comment about hot and cold. if the cold happens to be under water at the time then.........well, you get the idea.
Another place where "O" ring seals can be stressed is with your common wrist watch. Even a divers watch, if it repeatedly taken into a bath or shower on a person's arm, can have the seals fail and end up with the dreaded fog on the inside of the glass. Off to the watchmaker.

You have to remember that in service, this stuff can cop an absolute flogging. At MOD auctions you might get a goodun as in it was the pet of the Regimental Sergeant Major and it sat in a filing cabinet in the store. Or you might get one that has been run over by a tank. And all stations between.

I do know a little of this sort of thing as I was a radio mech in the Australian Army.

Cheers, Robert.

[G6Tanuki]

I've seen a couple with _extensive_ corrosion around the two battery-nubs: there's buggerall attempt at a seal between the spring contacts on the battery and the matching nubs on the radio. Water getting here will set up electrolytic corrosion between the nub and the case (the nubs being brass, the case being aluminium - about as far apart on the electrochemical-series as youcan get!).

Add in a nice steady 24V DC supply and the aluminium will be the loser in any electrochemical feud. Then once the seal between the case and the nubs is broken, and water gets inside....

[Thinking of electrochemistry, I'm reminded of a certain 1960s-manufacturer of combination TV Band I/III antennas who shot themselves in the foot by using brass wing-nuts to attach the connection-box to the aluminium dipole-elements. They usually lasted about six months before the connection-point was reduced to a white crumbly mass with vague green copper-stains as the only remaining evidence of the nuts.].

[QQVO6/40]

In the Australian Army some years ago we had a HF man pack portable field radio (PRC-F1). It had a threaded bulkhead type BNC connector made of nickel plated brass with a star washer under it to make good RF ground to the radio's front panel. The connector was for the external antenna.
Sounds good in theory. Good RF practice.
The plan was let down by the very light weight front panel casting which was made from magnesium. Once the corrosion started in the casting it was very difficult to stop.

Cheers, Robert.

[ex seismic]

While not the magnesium of the previous post, so it might be a bit different, while working on my Land Rover where there is corrosion of the aluminium I have found that brushing the loose white powdery corrosion away then treating with etch primer stops further corrosion. It doesn't of course fill in the corrosion pits, but any car body filler should do that if required - my LR doesn't justify that!

Gordon