Push to Talk failure - what caused it

[Guest Kevin the Penniless]

Hi. My pilot side push-to-talk (PTT) failed, no probs, just use the passenger side PTT. Nope, that doesn't work unless your head-set is plugged into the passenger side. So I landed with no radio calls. On the ground, all okay with the passenger side so that suggests the radio is ok. Get out my multimeter and check the pilot side PTT switch. Checks okay. Check the wires from the PTT switch back to the connector under the dash - one side is open circuit. Close inspection reveals two things. The first was very poorly soldered connections to the switch and second, the wires were 'nicked' badly when the outer insulation was stripped back. The 'nick' was the cause of the fault. I cut back and soldered the wires onto the switch, feeding the wires through the holes on the switch connectors first then soldering and slipping some heat shrink over for mechanical stability. The original soldering looked more like the person tried to 'glue' the wire to the switch.

 

 

 

 

[Dieselten]

Soldering is an art, and only those who have been shown how to perform the art can do it with any reliability. Soldering isn't just surrounding two pieces of metal with a shiny glob of another metal. Soldering involves a bond at molecular level between the metal of the wire being soldered, and the solder itself.

 

If you will forgive the pun, here are some soldering-tips:-

 

1. Use a temperature-controlled soldering iron.

 

2. Tin the tip before use, and clean the tip regularly, preferably before making each soldered joint.

 

3. DO NOT use Plumber's Solder - the acid in the flux will corrode wires for quite some distance!

 

4. Use only resin-cored 60-40 Lead-Tin solder. Avoid Lead-free solders, they are not suitable for avionics work. Good old reliable 60-40 electronic solder is your best friend.

 

5. Learn what metals can - and can't - soldered. Copper, brass, tinned copper and tinned brass will all solder very nicely. Aluminium is difficult to solder, even with so-called Aluminium solders. If your wiring is aluminium, use crimped-connectors in preference to soldered ones.

 

6. If you haven't the skill to solder successfully, find someone who has, or at least ask for some help from someone who knows about electronic soldering. DO NOT ask a plumber about soldering...theirs is an entirely different set of operational requirements using different fluxes and tooling.

 

7. A frosted appearance of the solder indicates too rapid solidification and the potential for a "dry joint". A properly soldered connection has the solder looking shiny and smooth and has the appearance of properly "wetting" the metal being joined.

 

8. There is a practical limit to the size of wires that can be successfully soldered. Really thick wires are likely to absorb so much heat from the soldering-iron that the adjacent insulation will be damaged before a successful joint can be made. Consider a swaged connection under such circumstances, it is as strong mechanically and almost as good electrically.

 

9. When soldering heat-sensitive components, use a heat-sink to prevent damage.

 

 

[Tomo]

An extremely good post there Dieselten. :thumb_up:

 

 

[Guest Kevin the Penniless]

Hi. Thanks for the reply, however, I am an Electronics Technician with some thirty odd years experience. That's one reason why I can be so critical of the lousy soldering job. Cheers and beers....

 

 

[Guest Kevin the Penniless]

There you go, some pictures to view....

 

 

[BigPete]

? Where

 

 

[Guest Kevin the Penniless]

The original post...

 

 

[facthunter]

Quality.

 

Thorough post diesel ten. The essence of soldering is cleanliness, the right temperature and nor leaving any corrosive substancas around after. I hate crimps. Nev

 

 

[Thalass]

You get what you pay for. :P This is why you need a proper avionics guy (or electronics technician!) to do avionics-type work. haha

 

 

[Guest Kevin the Penniless]

Well, the plane is built to a price, but that is no excuse for the lousy wiring. I reckon that maybe they get some old retired bloke to wire the loom for a bottle of port or maybe the kid down the street does it for pocket money. I'm still waiting for a response from the manufacturer. Just for the record - I have seen similar wiring in a $5 million business jet so I start to wonder what's going on....

 

 

[Thalass]

Yeah, that's why some people don't trust aircraft from a certain Brazilian manufacturer. Pull some kids off the street and give them a few cents pay per day... hah.

 

At least it wasn't something vital for flight. Might pay to have a look around at other wiring, though.

 

 

[Guest Kevin the Penniless]

Yes, I had a look at the wiring under the dash and it seemed ok to me. Like you say, better it happen to some 'non-critical' system. Rather a radio failure than say stuck flaps or undercarriage.

 

 

[Guest Maj Millard]

Yeah your right there Kev, deiseltens' post is spot-on though, good soldering is important and takes some skill to do consistantly. The solders in you post, while probabily effictive to a point, only rate about a from me....................................................maj...

 

 

[dazza 38]

Yeah, that's why some people don't trust aircraft from a certain Brazilian manufacturer. Pull some kids off the street and give them a few cents pay per day... hah. At least it wasn't something vital for flight. Might pay to have a look around at other wiring, though.

"EMBRAER" ?:big_grin:

 

 

[jcamp]

The most important soldering tool is some form of magnifying gear to ensure the wetting is OK.

 

For assessing joints in training we use a 25x stereo microscope. For normal use a headset magnifier (like the Jaycar one) is OK.

 

Where wires are joined to connectors crimping is better. This does not mean a $20 crimping tool, it means the type where the dies for a particular connector are $300+ - that's not the crimping tool just the dies.

 

After the electrical connection is made the next thing is to secure the wire to ensure minimal flexing at the joint. Where the wire is joined to the connector it is rigid and if soldered properly (ie proper tinning) there will be solder flow between the strands making the cable rigid for some distance along the cable. This solder flow may not be visible from the outside but in the case of instrument leads (several hundred strands) can extend for over 1cm on the inside. Where the strand goes from being rigidly fixed (crimp or solder) to being free any flexing (including vibration) will cause fatigue failure.

 

The aim is to ensure a transition between rigid join (solder or crimp) and the freely flexing cable; generally connector assemblies have some method of ensuring this (just look at your normal power plug). This can be approximated with 4 bits of heatshrink tubing (from the inside):

 

1. Piece covering complete join including any tinning extension or connector crimp on the insulator and 2cm along the cable

 

2. As above but 1.5 cm along the cable

 

3. As above but 1.0 cm along the cable

 

4. As above but 0.5 cm along the cable

 

 

[Thalass]

This is why engineers are so expensive. We have to pay for all this top-notch expensive equipment - never mind the parts! Guess who goes to gaol if CASA find something from Super Cheap Autos or something? heh.

 

 

[Guest Howard Hughes]

Perhaps a hand mike as a back up!;)

 

 

[Guest davidh10]

Kevin;

 

Would you like some Bunnings aircraft bolts to go with that soldering job:hittinghead: