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Old 12th Jun 2014, 9:44 pm   #1
hmv1944
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Default FT107 sticky relays

My 107 started to suffer from increasing delay in changing from transmit to receive. On the schematic there seem to be three relays involved in the tx/rx changeover and two are identical and mounted in sockets. So, I swapped them around and surprise, surprise, the problem has been (temporarily) solved! It is possible to remove the plastic cover of these relays to gain access to the contacts. But what is the best method of cleaning? On brief visual inspection the contacts looked clean, but there must be some sort of contamination there.
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Old 12th Jun 2014, 10:04 pm   #2
Little-Freddie
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Default Re: FT107 sticky relays

Hi!!! Don't know the FT107 specifically, but I used to clean old P.O. relay contacts by spraying a bit of thin card with an aerosol type switch cleaner, and (carefully!!) drawing it back and forth across the contact points. If you use white card, you may well be surprised at the amount of debris that shows up on the card, even from an enclosed relay!!!!

Good luck with it, (I'm currently working on an old FT101b, which I suspect, is a tad older than the '107!!!).

Cheers, Fred G4ZWI
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Old 13th Jun 2014, 7:00 am   #3
hmv1944
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Default Re: FT107 sticky relays

Many thanks, Fred. I was wary of using something like emery paper or even a nail file! The FT107 was the first all solid state txcvr from Yaesu, but too early to be run by a microprocessor or use a synthesised vfo.
Alan, G0BFM
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Old 13th Jun 2014, 8:09 am   #4
G6Tanuki
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Default Re: FT107 sticky relays

I'd suggest using an artist's painbrush dipped in IPA as your initial cleaning agent: it doesn't leave any deposits when it dries, and unlike some other contact-cleaning solvents used in times past (carbon tet, Perchlorethylene) it's also not 'strong' enough to dissolve any plastic parts.

I recall that spread over several editions of Practical Wireless a couple of years back, Harry Leeming G3LLL wrote a few notes on the care and feeding of the relays found in Yaesu transceivers of the 70s and 80s. Might be worth seeing if you can find a copy?
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Old 13th Jun 2014, 8:43 am   #5
m0cemdave
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Default Re: FT107 sticky relays

I have successfully used Fred's method - small strips of thin card / thick paper sprayed with switch cleaner - in this application.

At one time, you could get them ready-made from RS as "contact cleaning strips".

If the contacts are badly burned then more drastic treatment, or a new relay, may be required.

/ edit -typo
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Old 13th Jun 2014, 7:26 pm   #6
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Default Re: FT107 sticky relays

If you use a file or emery paper you will remove the plating from the contacts which can cause problems with the contacts becoming tarnished and high resistance in a short time. If the plating is burnt or very pitted its generally a good idea to replace the contacts or the relay for reliability. If high currents are involved the contacts can end up welded together if the plating is removed.
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Old 14th Jun 2014, 2:10 pm   #7
QQVO6/40
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Default Re: FT107 sticky relays

Hello all.

I have had a bit to do with relays and their larger brothers, contactors.
We are dealing with an electronic device here that is a few years old. Most things these days use plastics of may breeds for structure and insulation within them. Over a period of time with elevated temperatures the plastisizer tends to evaporate out of the plastic materials. Mostly it is an oily, sticky residue and it can condense on other components within the machine. A classic example of this is the interior surface of a car windscreen where the car is left out in the sun for a number of days during the hotter part of summer. Result is an oily film on the inside of the windscreen that is damnably hard to remove. Iso Propyl Alcohol (IPA) to the rescue.

The same oily residue can end up on relay contacts and for a relay that is slow to release, on the face of the pole piece and inside face of the armature.

As has been said above, suitable strips of good quality printer paper doubled over or single strips of Manila paper. (The type of stiffer paper found in Manila paper office folders.) Really, any type of good quality very fine fibre paper. Do not use news print as the fibres are too coarse and can end up lodging between the contacts.
My favourite is pure hemp fibre paper. The fibres are very long and very strong.
I put a few drops of IPA on the paper strip. Place the paper strip between the contacts and gently press the contacts together. I usually use finger pressure on the relay armature to accomplish this. Stroke the paper strip to and fro a number of times. I dampen the paper strip with IPA for the first few passes until I get no further colour from the contact or armature I am cleaning. Clean strip of paper for each pass.
Once I get to the point that I am not getting anymore dirt on the paper. I start to burnish the contact with just clean dry paper strips.
The wood used to make paper has within it's structure small amounts of silica.
This silica acts as a very fine abrasive and this feature can be used to burnish relay contacts without fear of removing much metal from them.
This abrasive action I learnt at an early age from my Aunt when I used her good dress making shears to cut some paper for something I was doing. My error was brought home quite swiftly!
If the piece of paper strip is difficult to draw through the contacts then I would start to suspect that the contacts may be burned. Further investigation would be needed to see how bad they are. There are special contact burnishing files available. The good ones have very fine powdered diamond dust on them and the tips are flexible. I have my own but would not know where to buy them these days.
Again I make the comment that a relay that is slow to release, quite often, has some of this oily scunge on the mating surfaces of the pole piece and armature.

I hope this has helped.

Cheers, Robert.
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Old 14th Jun 2014, 2:53 pm   #8
hmv1944
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Default Re: FT107 sticky relays

Many, many thanks everyone. Lots to work on there.
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