Vexing Volts.

[Peter Beeney]

Recently it became fairly necessary to have a battery charger at odd times, so I considered it a wise move to purchase some back-up. My existing box is reliable; and capable; but now getting very long in the tooth. So I acquired a standard run-of-the-mill type, but reasonable expensive, from our local model shop.

Straightaway I noticed that I was intermittently losing the 12 volt DC supply, frequently when the charger moved slightly, or even when just the wire flexed. I thought at first it might be the plug and socket, but it was soon obvious this was not so, so I had to get inside, which was very simple and straightforward. As I suspected, it then became apparent what the problem was, the two very poorly soldered joints on the DC jack socket on the PCB, photo 1. There are three tags for good support, but with two not soldered the socket was moving slightly, and breaking the electrical contact, under any strain.

Literally a couple of seconds with the soldering iron fixed it, photo 2, and, needless to say, the integrity of the supply is now 100% secure. I’ve given it the knock-n-shake test! I’m sure it could be argued that I could have sent it back, but that just involves more cost which ever way you look at it, plus hassle for the LMS, and undoubtably Sod’s Law would be lurking close by too, and I’d need it most when I didn’t have it! I will send the evidence to LMS, and he might possibly forward it on, but I don’t think it makes any impression anywhere anyway. As I’ve said before, I’ve sent a number of factual reports on some very iffy batteries, particularly rx, to suppliers and others, but I’ve never had an answer.

I did examine the PCB, but I couldn’t see any other discrepancies. Indeed most of it appeared to be be surface mount technology, only the odd peripherals, such as this socket, were hand soldered. I also removed that small solder flash, that’s part of the original soldering, I didn’t really want it falling in amongst the chips! Taking these photos shows everything up in detail that I wouldn’t normally see, for instance I’m sure that’s a hair-line crack in the original solder, bottom left hand side on the first tag, which I hadn’t spotted. I think the photos are actually very critical, I’m beginning to think that examining the picture is better than examining the component! From this point of view of easily seeing any small bugs just waiting to cause an disruption!

So for anyone noticing a frequent error message on the screen, this might be an answer……

Photo 1

Photo 2

PB

[Peter Beeney]

Recently I posted above describing a dry joint on the power socket connection in a brand new charger which was causing a touch of persistent hassle, now I seem to have found another. Or perhaps it found me.

A club mate bought a new ParkZone Mustang quite a while back, and in the process of flying it he rather broke it; … as you do. More than once or three times, as it happens. On one occasion recently it was again in a number of pieces so he passed them on to me as a gift. Well, that what he said, anyway. However, somewhat surprisingly, after repairing it, it turned out to be a little cracker, even though it was ailerons and elevator only. So I stuck a rudder servo in which then made it perfect.

Then suddenly last evening, when taking off for yet another sortie a rather careless self hand launch resulted in a little donk on the runway, nothing broken, but now the motor refuses to run, it just clonks over and oscillates to and fro.

Today I was contemplating buying a new one, (motor, that is), but I thought I would at least have a quick look in the meantime, and because of some luck and the fact that I try the easiest checks first, it took about thirty seconds to establish there was an open circuit between a banana plug and it’s associated motor wire. On removing the heatshrink I could see what the problem was, as in photo 1. On applying a hot soldering iron the dry joint was revealed in all it’s glory, that’s photo 2. The discolouring is the residue of the original flux, and not a trace of solder to be seen anywhere. I very much suspect that the wire was not tinned successfully when it was originally put together. A smear of Powerflow flux, the smokin’ hot iron, some multicore and few seconds of close contact, and the solder whizzed up the wire. Splendid job! Now the banana plug back on the end, top up with a touch more solder and it will never ever be an open circuit again. I also had a look at the red and black wires and plugs, and they looked to be soldered very nicely.

Connecting it up temporarily soon proved we had rotation again, so it all soon went back together ready for a few more missions tomorrow. But I think it’s really amazing that it’s gone all this time without giving some sort of trouble, and after all the big bangs one minor tremor was enough to cause it to let go; and also just how little surface area has to touch to pass all the current!! I had something similar years ago, too, a second hand speed brushed motor and speed controller in a powered glider I was flying at the time. Suddenly there was nothing working, most fortunately the model was on the ground, and this proved to be it’s connection to the battery, a Powerpole connector that someone had soldered on. The model, rudder / elevator only, used a BEC, and I must admit I was distinctly shaken when I thought of all the places on the limit of visibility that glider had previously been…..

In that case, I was able to pull the wire out of the soldered joint, with the wire showing a total lack of solder; very much like this one.

Photo 1

Photo 2

So yet again it just proves these things can strike out of the blue. Whenever possible it’s certainly worth taking a ganders at any connections. Also well worth having a look at any faults, too, I’ve thought for a long time that these are often mechanical rather than electrical in nature.

Hope this is worth posting.

PB

[Biggles' Elder Brother - Moderator]

I often wonder how many "mystery" crashes are actually cuased by intermitant faults due to dry joints. Interesting pair of posts Peter.

BEB

[TheFlyingCrust]

As an apprentice instrument maker all those years ago (late '60's) along with my fellow apprentices I was given task of learning how to solder. We weren't allowed near any proper electronics until we had mastered the art. And some found it a lot more problematic than others.

I use a tiny amount of plumbers flux with the standard ersin cored solder when soldering bullet connectors. Works a treat. I find the joint tins much more quickly. But do remember to clean off the flux residue after. Some fluxes are quite corrosive. Beware.

Ian