Power supply problems on Classic handsets.

divetheworld

Hi Guys,

There have been a few questions passed around relating to handsets which exhibit some problems which can be assumed to be due to power supply failures.
If your handset switches itself off for no reason when Master but works fine as slave, or shuts down at switch on, or wont switch on then there is a good chance that your battery terminals are buggered.
If you are not a clever clogs then just send it in to AP. They are a good bunch who will sort it out for you. However, if your a bit of a tinker and want to fix it yourself, then here is some help.

When the master handset is firing the solenoid for oxygen injection, you are getting a voltage drop from the extra power that is required to fire the valve. When it shuts down and polls in as slave it no longer controls the solenoid and no longer has the high current drain. That is why it is fine as a slave.
Assuming the battery is new/not faulty etc, then there are usually only two reasons for the problem.

1. Battery terminals - the contact points need cleaning and the wires on the back need a touch of the soldering iron to clean up a possible dry joint.

2. Power switch partial failure - the micro switch in the handset might have corroded contacts. This is common after many years of service and requires some heavy duty surgery. If your not happy with that then send it back in.

I strongly suspect the battery terminals as you get this problem long before you get a handset problem unless there are cracks in the housing that have let in seawater. You dont need to look to closely to see that problem, trust me, you will know it when you look inside!!

Here is the procedure to fix it. You will need an 8mm spanner or socket, a soldering iron, some solder, a damp sponge, a No.1 pozidrive screwdriver and a pencil eraser.

1. Remove the head from the 'breather and place on a nice clean table.
2. Using the big AP box spanner, remove the lockring from the top of the cell holder. Dont lose the blue slip ring.
3. Remove both batteries.
4. Remove O2 cell No.2 (the middle one).
5. Using the pozidrive screwdriver, remove the battery box by putting thre screwdriver through the hole where cell no2 was.



6. Using the 8mm spanner/socket, remove the nylock nut from the bottom of the battery box.



You will now see the battery terminal wires on the spring loaded pins. The solder will look pretty old and grey and dry. Using the soldering iron we will clean up the 4 terminals one at a time. Be very careful to use the minimum heat required to melt the solder and no more. Too much heat will melt plastic.
Heat up the solder with a tinned tip of the soldering iron until you melt the original solder, now flick it off. We want to renew the solder with fresh you see. You can clean the soldering iron tip with the damp sponge.
Only put on enough new solder to blob the end on the teminal and soak the wire end. Again, do not get it too hot. Take your time between heat applications.
Repeat this with each of the four wires on the terminals. Check the terminals are secure with your fingers. We dont want a dodgy joint.

This will not take you long to do. Test it before you re-assemble the head, dont forget to put cell No.2 back in for the test. Run a calibration so the solenoid fires up for a while, dont worry about using oxygen we only want the head to fire the solenoid to test for power drains. If it works fine then it's time to re-assemble. Put a little silicon grease over the soldered terminals to protect them before you re-assemble. The contact points inside the battery box need to be rubbed with the pencil eraser where the battery goes.
Your all done!



Brent

Usual caveats, competant person blah blah, safety shoes, goggles and nomex gloves blah blah. Pictures courtesy of Divermole, visit his site at http://www.btinternet.com/~madmole/DiverMole/DMnavigation.htm

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TheMacallan

Excellent.
Right, I've got the battery box sorted now how to you sort out those pesky micro switches.?
Photos would be nice too!!

Padowan

I have a unit that was new in the summer of 2004, and when I checked out the battery box wiring recently, I found that the cavity underneath the terminals is filled with silicone sealant. I am assuming that this is to reduce the possibility of moisture ingress here. If I want to solder the terminals I will need to pluck out the silicone sealant, and then re-fill afterwards.

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SimonK

I have never been a great fan of putting silicon sealant on connections. The sealant usually seperates from the wire / box letting water in and resulting in corrosion that hard to see and difficult to fix. Leaving it clean or putting a bit of silicon grease over the joint seems a better bet.

Simon

divetheworld

There are other problems with silicon sealant. Some of them off-gas significant amounts of acetic acid when it cures, if you dont get the right stuff then you will rot your copper connections worse than when you started out.
A blob of silicon grease on the solder when your done protects them from oxidation for a while.

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jknights

Brent,
Thanks for more Tips and Tricks.
Added to my Inspiration help files

divetheworld

this subject has popped up on PM recently, thought it could do with a bump.

In addition, dont forget boys and girls, that AP are replacing the battery boxes of this type with newer versions. Just watch out for getting the bill for the privilege.

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Mdemon

Great posts Brent - have a blob!

Question: Are the connections the same on the new battery boxes?

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divetheworld

Not different enough that you couldnt tackle it yourself matey.


brent

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Fun Under Pressure

Thanks for tip. Very helpfully.

Cheers Markku