Mystery fault

[Bob Abell 2Participant @bobabell2]

A club member turned up at the pond last night, to sail his latest purchase…….a used Fiesta yacht, about 2 years old.

When we switched on, it was totally dead, but it was working OK before he set out. We couldn't sort it at the pond side, so I took it home, hoping I could sort it out.

Spent a few hours checking the wiring, but without success

Went back to it this afternoon and it was working

Anybody got any ideas, why this can happen?

Could the crystals be a source of error?

Bob

A

[Bob Abell 2Participant @bobabell2]

[TelstarParticipant @telstar]

Hi Bob These type of faults can be most annoying. If the gear has not been used for a while I would first suspect the wireing in the Rx – switch – battery circuit. If the soldered connections to the associated plugs/sockets have insulating sleeve over them, I would check carefully to see if the connections under the sleeve have not corroded and are being held in place by the sleeve only. This type of 'dry joint' can come and go, usually giving up as soon as you try to take a bit of power from the battery , like using the sail winch or servo. If that showed nothing then it would be everything out and on the bench to run a full diagnostic.

Cheers Tom

Edited By Telstar on 21/08/2012 16:32:01

[shipwrightParticipant @shipwright]

Bob,

Difficult – could be a number of things.

Here is my two pennyworth of thoughts – battery ok (right number of volts when on load) ? – connectors ok ? – what frequency band is Tx (if it's 2.4 GHz then maybe Rx not synching with Tx) ? Have you any means of checking Tx (eg another compatible Rx) ? broken wire (I have experienced this with insulated wire – externally ok but wire is fractured inside the insulation) ? dry soldered joint ? screw connector not screwed up tight or screw is not in contact wire wire because of insulated not bared back properly ?

Regards.

Ian

[Bob Abell 2Participant @bobabell2]

Thanks chaps

I've checked most of the system and the supply to the Reciever was ok

That means the fault starts at the Rc…..somewhere?

The system is Hitec and all my stuff is Futaba……Sods law

At the moment, it is working, but don't feel confident for tonight's sail test……Will have the rescue boat close at hand

I suspect the Crystals for some reason

Fascinating problem………Bob

[Bob WilsonParticipant @bobwilson59101]

This appears to be an intermittant fault, maybe caused by the assumed car journey! A good way of locating intemittant faults is to get an electronic "freezer" aerosol. When the equipment is not working give it a squirt with the freezer. If it suddenly starts, you can narrow it down to the specific area on subsequent failures, but I would not recommend sailing it until it is sorted out! Reverse is often true and you can often bring the fault on by giving it a whiff of freezer!

I have used this technique to good effect on highly sophisticated marine transmitters and receivers and radar sets. I always have a can handy!

Bob

[Bob Abell 2Participant @bobabell2]

Thank you, Bob

I've never heard of such a magical device

How does it work and what is the spray made from?

Bob

[Paul TParticipant @pault84577]

Could the crystals have become damp

[Bob Abell 2Participant @bobabell2]

That's what I suspect, as the model has been in storage for some time

What exactly is inside the crystals?

It's club night tonight and all the experts will be there, perhaps even the previous owner?

Bob

[shipwrightParticipant @shipwright]

In the context of RC Tx and Rx, a crystal is an electromechanical resonator. The active component is a specially cut small slice of quartz which has a number of resonant modes. The associated electronic circuit (which is external to the crystal) is designed to get the crystal resonating at the desired frequency (often not the fundamental resonant frequency but at some multiple of that frequency). Normally the crystal is hermetically sealed in its container so unless the crystal has been damaged the crystal is operating in a vacuum. The crystal in the Tx determines the operating RF channel of the RC system and that in the Rx is offset in frequency by the intermediate frequency (IF) of the superhet receiver. Hope this brief explanation helps – the subject of oscillators is a big topic in its own right.

Ian

[shipwrightParticipant @shipwright]

In the context of RC Tx and Rx, a crystal is an electromechanical resonator. The active component is a specially cut small slice of quartz which has a number of resonant modes. The associated electronic circuit (which is external to the crystal) is designed to get the crystal resonating at the desired frequency (often not the fundamental resonant frequency but at some multiple of that frequency). Normally the crystal is hermetically sealed in its container so unless the crystal has been damaged the crystal is operating in a vacuum. The crystal in the Tx determines the operating RF channel of the RC system and that in the Rx is offset in frequency by the intermediate frequency (IF) of the superhet receiver. Hope this brief explanation helps – the subject of oscillators is a big topic in its own right.

Ian

[Bob Abell 2Participant @bobabell2]

Thank you, Ian

You certainly know your onions!………And crystals

The previous owner did say it got very wet inside the hull.

Water in the receiver wouldn't do it any good either

Bob

[ashley needhamParticipant @ashleyneedham69188]

The quickest way to fault find, after having done the usual checks ..loose connections, wiggling the equipment, unplugging and re-plugging all the connectors and leads.. is to simply substitute parts.

It is no good looking for faults on intermnittant equipment when it is working as there is not much to see..as it is working. When it stops… swap something. There is nothing worse than intermittant faults, makes sailing (or whatever) a right pain.

I am sure you have spare items.. recievers, ESC (or board in your case) batteries, Rx packs.It is the way to go. Crystals, I would have thought, were sealed or encapsulated in..stuff.. and would not suffer from damp?? water on the ariel would throw a spanner in the works.

Ashley

[Bob Abell 2Participant @bobabell2]

Thank you Ashley

As I have already mentioned, the Fiesta is all Hitec stuff and I've only got Futaba

The problem is that it ceases to work without touching anything

Could be a genuine Gremlin?

Bob

[Bob WilsonParticipant @bobwilson59101]

This sounds like a job for the freezer aerosol. It comes in a normal size aerosol can. For years I found it invaluable when at sea and it would often pinpoint intermittant faults that had previoulsly eluded all other methods. Maplin do a freezer spray for about £7 a can (444ml).

Here is a link to more details:

**LINK**

I always preferred the simplest methods when fault finding, but have always been surprised how few technicians use it!

Bob

[Bob Abell 2Participant @bobabell2]

Thanks for the info, Bob

But, tonight the Fiesta yacht sailed without a hitch

So at the moment, it`s panic over

Thanks for your suggestions, chaps

Bob

[DuckyParticipant @ducky]

Boat sailed al-right last night, though not much wind after the torrenial downpour!, must have been damp inside after not much use over the last few years.

Duckie

[Bob Abell 2Participant @bobabell2]

Just for a bit of background information

The new owner of the Fiesta is new Etherow club member, Charlie……A very young at heart, sprightly 85 year old!

He has recently joined the club, having built his first model, the Italeri Torpedo boat, which sails well.

He then fancied the Fiesta racing section, hence the Fiesta

Previous the this he saw the Club 500 boats…….and is now building one

He then visited the Steering Comp…..You've guessed it……….He' building one of those too!

But he really fancies one of the big J Lass yachts, but alas!……It won't fit in his car!

I think, model boating has given him a new lease of life!

All the best, Charles………Bob

[Malcolm FraryParticipant @malcolmfrary95515]

Cleaning (by a bit of light abrasion if the legs look at all tarnished) of the crystal legs might help. This must be done gently – while crystals are generally incredibly tough, the metal of the legs is brittle, and the hermetic seal can easily be damaged.

Check supply voltage under load, at the battery, at the RX end of the lead (remember that the switch, if fitted, and its associated joints can give problems). If its all playing dead, less likely canditates are the servos, but it is possible for both to go faulty at the same time. Unlikely, but still possible.

Check the RX aerial lead for any unexpectedly bendy bits in the area of it exit from the box. If the wire is broken inside the insulation this can give problems, but this can be eliminated if the servos dont twitch at power-on.

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