Trouble with old SM3s

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Trouble with old SM3s

#1

Post by RSR Engineer » Sun Mar 08, 2020 11:41 pm

After singing the praises of the old H&M SM3 point motors, I have to confess I'm now having quite a problem with them. These SM3s are attached to the underside of the various baseboards, which were stashed in a cold, damp, uninsulated attic for quite a few years. The boards and tracks survived this very well but I now find, in the course of circuit testing, that the auxiliary switches on the SM3s won't pass any current. I suspect it's due to tarnishing of the phosphor bronze wipers and/or oxidation of the aluminium studs. I tried to "polish" these with a piece of emery paper but they're hard to get to and no amount of scrubbing seems to make any difference.

Have any other members had this sort of trouble? I would appreciate any information and/or advice I can get.

An alternative solution I'm exploring, should the cleaning attempt fail, is to install supplementary micro-switches operated by the point rigging.

Cheers and many thanks in advance,
Artur

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Stese
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Re: Trouble with old SM3s

#2

Post by Stese » Tue Mar 10, 2020 3:03 pm

Emery board may be a bit harsh for what you are doing...

You could try a combination of a fibre pencil and some isopropyl alcohol if you can reach the contacts.

Could you post a picture?
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Brian
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Re: Trouble with old SM3s

#3

Post by Brian » Tue Mar 10, 2020 4:19 pm

Hi

I have had several of these old Hammant & Morgan solenoid motors fail with both to move correctly or their contacts not making correctly. I found that a light spray with a contact cleaning fluid worked very well especially after the motor was hand moved over and back several times to work the fluid into the contacts. This is a typical example (there are many others) Link to example

I also found that a little light oil, as used for loco lubrication (Not WD40 type) applied to the solenoids moving iron core on both sides so as it works into both coil former's helped greatly too.

Finally I found a CDU is almost essential with these motors. ;)
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Re: Trouble with old SM3s

#4

Post by RSR Engineer » Sat Mar 14, 2020 10:07 am

Many thanks for your feedback and advice, gentlemen.

Stese, I'm attaching a picture of the SM3 seen from underneath, as it were, which shows how awkward these contacts are to get to, even when not mounted on the underside of the baseboard and wired in. Harsh or not, emery didn't do much good. Brian's idea of a contact cleaner, which looks like the way to go, led me on a wild goose chase to my local DIY (not Brian's fault, let me stress), where they offered me some anti-dampness spray for the car ignition that contained (flaunted on the can) penetrating oil, so that was a Schaffhausen. I ended up ordering the market-leading stuff (Kontakt 60) from Bürklin, a leading supplier in Munich. Once this arrives, I'll be able to put it through its paces.

Cheers and, again, many thanks,
Artur

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Re: Trouble with old SM3s

#5

Post by RSR Engineer » Wed Mar 18, 2020 12:56 pm

That stuff has transformed my SM3s entirely. The meter shows virtually no resistance across the conatcts.

Many thanks again, Brian.

Cheers,
Artur

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Re: Trouble with old SM3s

#6

Post by Brian » Wed Mar 18, 2020 1:09 pm

Pleased to read you have them working again.
A light spray of contact cleaner once a year etc will (or should) keep them in tip top condition. :D
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Re: Trouble with old SM3s

#7

Post by RSR Engineer » Wed Mar 18, 2020 10:47 pm

Yes, Brian, I'll bear that in mind. Thank you.

Cheers,
Artur

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