Estranged pieces of metal in an Organ from the 1960s are the topic of the day

September 7, 2009 11:33 AM

Fixing an old transistor organ: how do I fix these switches that seem to rely on the springiness of metal in order to make contact?

So, I'm working on fixing this big ol' Doric organ (previously), and I stumbled upon a big break: it appears that the voices, as well as the vibrato, may not be broken, but just the switch activating them. However, this switch seems to rely on the exact same principle as the key contacts, and that principle is failing hard fourty-something years after this thing was built.

See this picture for a quick hint.

Basically, two wires, one which is the contact and stays at a certain place, and the second which is supposed to spring onto that contact when the key is depressed. Unfortunately, the second one is no longer very springy and I believe that these contacts are a bit rusty/bad.

So, contact cleaner is obvious solution #1, but the other problem is that with a few of these buttons, the piece of metal which is supposed to move onto the other just doesn't, and I don't have much of a way of bending it, since the furthest it can travel right now is the other contact. Also, just rebending this wire is a temporary fix, I'd guess, since, after all, it'll bend back like it has over all these years, leaving the next aspiring electrician thinking that the vibrato circuit is broken.

So, please let me know your thoughts! I am not even sure what the term for this 'keying system' is called, so my google-powers are weak. And any help would be so, so appreciated!

Thanks!

posted by tmcw to technology (5 answers total)

Sometimes you can bend this type of thing sideways, bring it through the gap, over bend it, then spring it back down and sideways into the original position.
posted by weapons-grade pandemonium at 11:44 AM on September 7, 2009

In the lab, we used to find "broken" switches on old oscilloscopes quite often. You shoot the mechanism with blue electrical switch cleaner like this, agitate the connection by pressing (or in our case, rotating) the switch a few dozen times, and see if the corrosion has been cleared away by the spray. Greater than 50% success rate. At least you may halve the number of switches that need further mechanical adjustment, or replacement with a modern microswitch.

The stuff I remember using was called Blue __________, but I can recall what. And I can't find it for sale on the internet because likely it was full of nastiness currently known to cause cancer.
posted by fatllama at 12:24 PM on September 7, 2009

Any way you can use a rocker switch, or some other switch underneath the existing rocker tab?
posted by orme at 3:04 PM on September 7, 2009

3 things from my electromechanical telecomms days...

1. Clean & polish the contacting surfaces - something like this is good (but the contacts need to be washed down afterwards with contact cleaner to remove grit etc).
2. The contacts should not only touch, but wipe - that is, there should be movement past the point of contact. This helps a) ensure a good connection, and b) keep it clean & quiet.
3. I can't find an online description of how to retension springsets/contacts, but if they genuinely are spring steel wires it can be done. It's a bit of an art and takes some practice, but the basic steps are:
   1. Straighten the contact spring, usually by drawing it through a pair of smooth-jawed pliers. This also removes any tension in the spring. The purpose here is to straighten it, not tension it.
   2. Put some "set" onto it with a springset tensioning tool. This is the bit that's hard to explain without pics. Imagine grabbing the contact between your index and middle finger, perpendicular to the length of the contact, then twisting your hand while moving along the length of the contact. This, if you do it right, results in a contact with a fair bit of tension, contact pressure, & stiffness, but which is still straight.
   The real trick is to do it without bending the contact, or overdoing it and immediately taking away the set you've just put on. As I said, it's an art, and you need to develop a real feel for it to be able to do it successfully. If I find pics of the tools or technique I'll come back and link to them here.

posted by Pinback at 3:46 PM on September 7, 2009

Thanks everyone, heading down to the friendly neighborhood hardware store to look for a contact cleaner & maybe a microscrub this afternoon.
posted by tmcw at 1:54 PM on September 8, 2009