Repairing/cleaning rotary switch

[uoficowboy]

I have an HP power supply with a rotary switch on it that is not in the best of condition. The contacts often measure as having 100+ ohms of resistance (or are completely open), and just tweaking the knob a little bit will make that change wildly. I've tried cleaning with IPA and q-tips, but that has only improved things somewhat. Part of the problem is that it's very hard to get at the contacts - I'm tempted to take apart the whole assembly, but I'm also worried that it may be troublesome to get back together.

Anyways - what have you all found to be effective for cleaning rotary switches? And have you found it necessary to take them apart to clean?

[robrenz]

IMO you cant beat taking it apart if that is possible. If you are concerned about getting lost in putting it back together have someone video the disassembly so you can see where things went. If no video take a bunch of still shots at every half step. video is better because it will catch the trajectory of that spring that goes flying to who knows where and you will have a hunch where to look for it.

After cleaning all the parts with IPA I like to use Deoxit D100L liquid to clean the contacts. if possible I clean the contacts with a soft stick (trimmed popscicle stick) wetted with the D100L  If the stick wont fit I use a small tab of heavy printer paper in a hemostat wetted with the D100L and swish it back and forth between the contacts to remove all oxides.  Now clean everthing wtih IPA again and lube the contacts with Deoxit G100L liquid. not dripping just wetted, If you have compressed air blow the excess off. Re-assemble and cycle the switch about 30 times to burnish in the new contact pattern and it will probably be better than new

[BravoV]

......video is better because it will catch the trajectory of that spring that goes flying to who knows where and you will have a hunch where to look for it.

No video though, for this kind of job of dismantling a small gadget with possibly springy things inside  , I used a medium size clear transparent plastic bag, cut two holes that big enough but not too loose for my two hands to slip in quite snugly, and with some small hand tools inside to do the work.

No more worry of finding those pesky little thingy that sprung across the room and landed into no-where land. 

[robrenz]

Nice Idea 

Edit: But the video will catch where the spring needs to go back in when you assemble it.  Use the bag and video

[uoficowboy]

IMO you cant beat taking it apart if that is possible. If you are concerned about getting lost in putting it back together have someone video the disassembly so you can see where things went. If no video take a bunch of still shots at every half step. video is better because it will catch the trajectory of that spring that goes flying to who knows where and you will have a hunch where to look for it.

After cleaning all the parts with IPA I like to use Deoxit D100L liquid to clean the contacts. if possible I clean the contacts with a soft stick (trimmed popscicle stick) wetted with the D100L  If the stick wont fit I use a small tab of heavy printer paper in a hemostat wetted with the D100L and swish it back and forth between the contacts to remove all oxides.  Now clean everthing wtih IPA again and lube the contacts with Deoxit G100L liquid. not dripping just wetted, If you have compressed air blow the excess off. Re-assemble and cycle the switch about 30 times to burnish in the new contact pattern and it will probably be better than new

I think a video is a good idea, and a video while doing everything in a bag is a great idea. I'll give that a shot.

I've heard of the Deoxit products - but never used them. Do they represent any danger to the device being cleaned? Does it need to be washed off? Well, really, how exactly do you use it?

[robrenz]

Caig technical page read the pdfs linked on the left side of the page.

What I already described is IMO optimum.  Some people just use the Deoxit (D100L) and leave that on. The G100L is a superior lube/sealant/corrosion inhibitor. That is why I reccomend cleaning off the G100L and applying the D100L.

You might want to read this thread about the same stuff.

[uoficowboy]

Caig technical page read the pdfs linked on the left side of the page.

What I already described is IMO optimum.  Some people just use the Deoxit (D100L) and leave that on. The G100L is a superior lube/sealant/corrosion inhibitor. That is why I reccomend cleaning off the G100L and applying the D100L.

You might want to read this thread about the same stuff.

Sorry - somehow I missed that you specified how you use the products in your earlier post. Maybe I need my eyes checked...

Regarding the G100L - how important do you think that is? It seems to be the spendier of the two, and the D100L already is pretty spendy.

[robrenz]

This is what I base my opinion on from the Caig literature:

When do I use DeoxIT ® vs DeoxIT® GOLD vs DeoxIT® SHIELD ?
--------------------------------------------------------------------------------
DeoxIT® .
General purpose cleaner, for all metal surfaces with severe oxidation and corrosion. If there is a discoloration of the metal - it is considered severe. Use DeoxIT® to dissolve contamination, as well as lubricate and protect the surface. For reference, DeoxIT® has approximately 20% cleaning action.

DeoxIT® GOLD.
For plated surfaces (gold and other precious metals). Recommended for critical applications where only slight cleaning action is necessary. For reference, DeoxIT® GOLD has approximately 0.5% cleaning action. If the surface looks clean, applying DeoxIT® first is usually not necessary. If small amounts of oxidation are present on the surface, DeoxIT® GOLD will dissolve this. Apply DeoxIT® GOLD after DeoxIT® on plated metal surfaces, except where noted with DeoxIT® SHIELD below. The more critical the connection/part, especially low current applications, DeoxIT® GOLD should be the final step.

You can get the G100L in 2ml tube for $6.95 and the D100L in 2ml tube for $5.95

 

[uoficowboy]

Well, I ordered up this kit: http://www.amazon.com/gp/product/B0018KNHRY

Tonight - I took apart my old power supply, and even disassembled the rotary switch. Some of it was riveted together, so I didn't go beyond that. I cleaned off the wiper with the DeOxit and a cue tip. At one end of the wiper it was pretty blackened, so I used the wooden end of the cue tip to knock out the last of the blackness. I then took a kimwipe and tore off a very small chunk of it. I was able to get it around the wiper, then soaked it in some DeOxit and rotated it through the contacts a couple times (they were too tight to get anything inside of them). I repeated that until the kimwipe came out looking clean.

I cleaned with IPA and then dried. Next, I applied the DeOxit Gold using the same procedure I used for applying DeOxit.

Contact resistance went from ~100 ohms on the worst contacts to less than 1 ohm on the worst contacts. Current sensing now works great! Now I just have to fix one last problem on one of the channels and the device will be fully operational again

Thanks for the help!

Edit: actually, after reviewing the schematic for my supply - the behavior I'm seeing (that I thought was my one remaining problem) is by design. This power supply is fully operational now .

[nctnico]

The only solution is to replace a bad switch. A switch consists of a base material and a contact layer. Once the contact layer has worn off the switch is broken. Maybe re-plating the contacts can be done.

So called contact cleaners all have in common that they contain some kind of acid which eventually will corrode the base material, surrounding circuits and wiring making the problems only worse and a proper repair next to impossible. Contact cleaner gives you time to buy a new piece of equipment. Forget about repairing a piece of equipment after using contact cleaner on it.

[robrenz]

I respectfully disagree.

Some contacts may be worn out as you described. But I think many more are just corroded and or dirty
If what you say is true why does Agilent supply deoxit with the 34420A nanovolt/micro ohm meter and tell you to use it on the bare copper test lead connections?  There is definitely no acid in deoxit or deoxit gold. Many forum members have long term success with deoxit contact cleaning products

Edit: I have no connection with Caig I just like their products.

[nctnico]

And the source of the problem is right in front of you: copper oxidizes so every time contact cleaner is applied you etch away some copper. The fact HP is suggesting contact cleaner (perhaps because their connector is designed for it) doesn't make it a good overall solution.

Like I typed before: a contact consists of several layers each with a specific function. The contact layer is usually a material which doesn't corrode easily and makes a good contact. If a contact is dirty just clean it with IPA (alcohol). If it is corroded then it needs to be replaced because the contact layer is already gone. There really is no snake oil solution despite reported succeses with contact cleaner. Contact cleaner only works for a while but in the end it makes things worse. Its like using heroine to get rid of a headache.

Over the years I have seen lots of equipment ruined beyond repair because somewhere in its lifetime someone thought using contact cleaner was a good idea.

[mzacharias]

And the source of the problem is right in front of you: copper oxidizes so every time contact cleaner is applied you etch away some copper. The fact HP is suggesting contact cleaner (perhaps because their connector is designed for it) doesn't make it a good overall solution.

<snip>

Contact cleaner only works for a while but in the end it makes things worse. Its like using heroine to get rid of a headache.

Over the years I have seen lots of equipment ruined beyond repair because somewhere in its lifetime someone thought using contact cleaner was a good idea.

I have cleaned and repaired thousands of switches in my career and while replacing the switch with a BRAND NEW switch (not new old stock) would certainly be optimal, most of us have to live in the real world.

We CAREFULLY clean the switches and contacts realizing the process may need to be repeated in the not too distant future.

Economics, time constraints and parts availability dictate what practical options exist.

It might be nice not to have such limitations, but in reality this is not usually the case.

[nctnico]

Like I typed: Its like using heroine to get rid of a headache. Once you start you have to keep using it.

I don't see how cleaning a switch over and over again (every few weeks/months?) is more economic for the customer than replacing a switch (maybe use a better quality switch) and have the equipment work without problems for years/decades. Labour is expensive but your boss knows that having his customers  'addicted' on cleaning will provide him (and you) with a steady income.

[G7PSK]

There are switch cleaners that do not contain acid, most times that I have had to clean switches the problem has been due to dried up grease rather than corrosion, I mostly use benzine (lighter fuel) or spray cleaner that is a hydrocarbon solvent and lubricant, I would not dream of using an acid on any electrical contact. I have seen what just tiny amounts of acid can do to spring contact, totaly denaturing things like phosphor bronze springs to the point they break. For more stubborn dirt I use a piece of fine ribbon soaked in solvent that I draw back and forth through the contact like dental flossing.

[mikes]

nctnico obviously has had no direct experience with DeOxit. It's good stuff, doesn't cause problems, and is not only recommended by high end manufacturer's (HP and IET Labs, for two), but many of Caig's products even have military NSNs.

But haters gotta hate.

[madires]

There are switch cleaners that do not contain acid, most times that I have had to clean switches the problem has been due to dried up grease rather than corrosion, I mostly use benzine (lighter fuel) or spray cleaner that is a hydrocarbon solvent and lubricant, I would not dream of using an acid on any electrical contact. I have seen what just tiny amounts of acid can do to spring contact, totaly denaturing things like phosphor bronze springs to the point they break. For more stubborn dirt I use a piece of fine ribbon soaked in solvent that I draw back and forth through the contact like dental flossing.

I use a tuner spray, which removes the corrosion in a quite soft way and applies a film of oil to prevent new corrosion (or delays that at least) and also lubricates the mechanics. Worked great for potentiometers and rotary switches so far. For more solid parts with heavy corrosion like contacts of plugs/sockets I use a contact cleaner first and then apply the tuner spray. Of course, if the contacts are worn out the only fix is to replace the bad part.

[klimm]

Is there any conductivity data about DeoxIT  or other contact cleaners ?

In this flyer   https://acct113328.app.netsuite.com/core/media/media.nl?id=793&c=ACCT113328&h=cf9f74b54878595f50b4&_xt=.pdf
there is a statement suggesting conductivity :The unique conditioning solution improves conductivity and provides long-lasting protection on Gold, base metals and other precious metal contacts and connections.
Further: Conduction through a DeoxIT® Gold coated surface takes place in three ways...   

On the other hand a rotary switch is built on a good insulator which could be compromised by a conductive layer.

I just washed and hot dried some old switches built on paper-phenolic substrate('70s I think)  and I would like to protect the contacts but it will be used in a null detector(small voltages, small currents)  As the substrate itself (paper-Phenolic)  is not a fantastic isolator I don't want to spoil it totally by using a conductive grease of some sort.
Vaseline could work but would eventually gum(dry out)?
Any suggestions please?

[madires]

It's not conductive, the oily film on the contacts mitigates oxidation and provides lubrication. Hence the "improves conductivity" marketing speak. It can't turn contacts into superconductors. But for low-leakage applications you should check if CAIG provides any data about DeoxIT's resistance.

[klimm]

Thank you Madires,
I already did. No data found. Marketing is also what I found in the Chemtronics Guide. When you want to hear conductive they say conductive, when need isolation they say non conductive
For cleaning I  use to use R-11  https://www.duecielectronic.it/index.php?lang=eng&menu_1=prodotti&menu_2=R-11&cat=pulizia but also here not much help Curious what do users of Fluke 845 or HP419 use?
I have an old Feussner compensator. That one  has mineral oil on the switches

[computerlen]

If I may add to this post, I would say that I have been applying contact cleaner/enhancer to switches, potentiometers, and input/output jacks in musicians' amplifiers for decades. Over 90% of the repairs that come to me require cleaning. Corrosion is the cause. De-oxit works as do other products that are safe on plastic. Maybe a couple of my customers have come back in two or three years to have it done again.

[klimm]

For usual applications I have no doubt  it works, I  also use contact cleaners.
I raised the concern only because my application requests  low leakage, say uV or even nV and really low currents too.