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· Just another modeller
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*** That is becasue the wire is nickel-chromium (NiChrome) wire. It needs a different flux and a solder with lead/tin/silver in it.

An old toaster element can be handy to replace it. If you unwind it totally and measure the length, you could also buy NiChrome wire from an electronics supply house and re-wind it.

If exactly the same diameter isn't available (within 0.1mm) rejoin the two broken bits temporarily by twisting together tightly them measure the overall resistance.

Buy the nearest diameter and measure the resistance along its length until you reach the same figure or slightly more, then cut to THAT length and use it to re-wind the mat. (if its thinner the replacement will need to be be shorter, if fatter it will need to be longer)

regards

Richard

QUOTE (Dave Saunby @ 18 Feb 2013, 04:26) <{POST_SNAPBACK}>Thanks for the info.

We found the fault on the P5 controller. The speed control windings had broken, and for some reason would not take solder to rejoin.
 

· Just another modeller
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9,967 Posts
*** This is how I would do it if I didn't use spray glue, which might be a little unforgiving to work with on such a big sheet especially if there is only one pair of hands to do it with.

Take a portion of the PVA glue and thin it with Windex (window cleaner), then roll it onto the board surface as a primer. Let it get mostly dry.

With the rest, add 1 part warm water and 1 part Methylated spirits to several parts glue (or 2 parts Windex to 2 parts glue) and roll it onto the back of the sheet.

Mist the area you will place it with Windex to re-damp it and make it tacky again. Wait a couple of minutes then lay the sheet...

8x4 is a big sheet to lay. Start at the middle and ease it out in both directions, rubbing down with a clean dry tea towel of similar. if it takes a while re-damp the un-laid bit with Windex to keep it tacky.

Regards

Richard
 

· Just another modeller
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9,967 Posts
*** Did you use the alcohol in the mix as I recommended?

It aids flow and penetration of the glue.. which is why I suggested it. Even a misting with windex (which contains alcohol) will make a big difference.

A big sheet loke that also needs rolling into place - The rolling is important even if it looks flat as its laid... its not enough just to lay it...

Richard
 

· Just another modeller
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9,967 Posts
*** Any water-clear (or slightly blue tinted) window cleaner will largely be alcohol and water with a tiny bit of non foaming detergent - brand isn't important.

regards

Richard
 

· Just another modeller
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9,967 Posts
*** No need to over think it.

All it has to do is act like a wetting agent to improve the bond. Simple water+methylated spirits would do fine, but I'd bet most of the window cleaners you looked at would too - the labelling shows the toxic additives (Methylisothiazolinone is a strong preservative / anti fungal that's there in tiny amounts) and I'd bet that alcohol in some forma or another is in there too.

Richard
 

· Just another modeller
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9,967 Posts
*** Tom, being a very old mains power controller, to be up front about it - and I do not want to offend but:

(1) It is a dangerous device to fiddle with in that it is metal cased and an error in working with it may well result in some risk of electrocution.

(2) It is such a simple device internally that to be honest, if you need a diagram to fix it you should probably NOT be the one fixing it!

(3) It is bad enough that it is already so far below current safety requirements that it could never be officially "sold" today - but think - if you are not qualified, but work on it and it later catches fire, guess what the insurance company will say.

I am not one to harp on about safety, but some things just aren't worth it.

Richard
 
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