Safe Switch Cleaner

[andy3055]

Hopefully, this is the right place to ask this as it is particularly related to oscilloscopes.

Given the nature of the rotary multi-position switches used in the older Tektronix scopes, what would be best used to clean them without going in to detailed dis-assembly (even if it can be taken apart)? Something that can be sprayed in without damaging any plastic parts (that may be) within the assembly and also that will not leave any residue?

I have heard horror stories of some of this stuff damaging plastic parts after some time. Any suggestions will be much appreciated.

Thanks.

[labjr]

I use Caig Deoxit for cleaning all types of contacts and switches. Have been for many years. I think it works great. It does leave some residue but I've never had it harm anything.

[andy3055]

Thanks, that looks good.
Regards.

[Gyro]

Well in the case of older Tek attenuator switches, their only Tek recommended method is applying IPA to a strip of non-clay paper and sliding it between the closed contacts (closing after insertion) with a horizontal action.

Normally (thinking Tek 4xx) you can do this after just removing the attenuator lid.


P.S. If you do decide to risk something like Deoxit, then you should apply it to the contact points alone with a fine probe rather than spraying the entire substrate, if you want to avoid changing the attenuator characteristics. I once had intermittent noise problems on one channel of a 475A which I finally traced down to an eyelash lying on the substrate tracks (not obstructing the contacts).

[nctnico]

Hopefully, this is the right place to ask this as it is particularly related to oscilloscopes.

Given the nature of the rotary multi-position switches used in the older Tektronix scopes, what would be best used to clean them without going in to detailed dis-assembly (even if it can be taken apart)? Something that can be sprayed in without damaging any plastic parts (that may be) within the assembly and also that will not leave any residue?

I have heard horror stories of some of this stuff damaging plastic parts after some time. Any suggestions will be much appreciated.

In my experience contact sprays are to be avoided. Most are corrosive and will eat away metals in the longer run. Things get even worse when the wiring wicks the contact spray to other places. I've seen very nice equipment being destroyed by contact spray. I'd use IPA to clean the contacts but if a contact is worn then the only long term solution is to replace it. Once the contact plating is gone you'll keep having problems. Contact spray is a temporary solution to make a piece of equipment work for a short while but after that it is ready for the bin.

However before washing with IPA I'd take a good look at the switch. It may be lubricated at some points and IPA will wash away the lubrication as well so you'd have to take the switch apart. All in all the easiest solution is likely to find a replacement switch if the switch is bad and do nothing if the switch is working OK. If it ain't broken don't ruin it. If the switch is working fine right now then anything you do to it will likely damage it.

[VK5RC]

In my very limited experience, I have used the paper/IPA for a very light 'abrasive' clean, and then de-oxit as a minimal residual switch lubricant.

The only problem I see with the 'spray it all over' technique is you may 'wash' some of the heavy grease from the shaft bearings onto the contact area.

As he is a professional in the high tech area (microwave +) , I value Shariar's opinion highly.
See the YouTube below
https://youtu.be/8uH-3-e2U3E
Rob

[andy3055]

Thanks to all who responded. I will first try the IPA method first. I don't believe replacements are available for these anyway. I wanted to gather some info before I got started.

Thanks to all.

[tkamiya]

I wanted to let you know, IPA method isn't absolutely safe either.  IPA itself is relatively safe but what is often sold as IPA from regular stores are de-natured.  They are often mixed with numerous things including gasoline.  (often labeled as 70%)  You can try cleaning mirrors and let it dry.  You can often see oily residues.  So be careful.  In United States, if you look hard enough, you can find 90% kind.  99% is also available.  (even from places like Amazon!)  They are safer from de-naturing prospective.  I have only seen 100% from chemistry supply stores.  I have 70% and 99% and use them depending on what exactly I am doing.

I use De-oxit as well, but with some care.  Sometimes spray some into a container and use syringes (I have lots...  I am diabetic) to apply precisely.  De-oxit spray has very bad tendency to spray all over the place.  I had varying degree of success.  So far, I haven't had any case it caused damage.

There's really no 100% sure way of dealing with old switches.  I think, the best you can do is be familiar with various methods, and use small amount first. 

[andy3055]

Agreed. Since these are very old switches, no telling what effects they will have. I have seen 90% but even that was kind of rare. I guess I will have to hunt around or order from eBay.

Thanks for the tips.

[tkamiya]

I forgot to mention....  don't neglect physical method of cleaning either.  I used to clean relay contact and rotary switches using business card stocks.  They are just rough enough to take the oxidation layer off without grinding off thin plating.  Carefully slide clean card stock between layers few times.  Worked especially well on relays.

If you need certain parts, you could always ask for one here.  Myself, I have a garage full of for-parts-only stuff.  Some of us will be glad to take parts off and send it to you.  I'm in US, and I once received a small part from Australia.  I've also given away spectrum analyzer parts.

What kind of Tek scope is it?

[andy3055]

I forgot to mention....  don't neglect physical method of cleaning either.  I used to clean relay contact and rotary switches using business card stocks.  They are just rough enough to take the oxidation layer off without grinding off thin plating.  Carefully slide clean card stock between layers few times.  Worked especially well on relays.

If you need certain parts, you could always ask for one here.  Myself, I have a garage full of for-parts-only stuff.  Some of us will be glad to take parts off and send it to you.  I'm in US, and I once received a small part from Australia.  I've also given away spectrum analyzer parts.

What kind of Tek scope is it?

Ah! You are so generous! Let me give a little history. I posted elsewhere on EEVblog (https://www.eevblog.com/forum/repair/tektronix-465m-repair-210933/) about my 465M that died due to my accidentally leaving it overnight. Now, after spending almost close to $200 or so, I am still down with it as it seems like the HV transformer is possibly faulty.

In the meantime, I came across a 465 that I picked up yesterday. It seems like the Ch2 Input coupling switch is intermittent in making contact. I have still not opened it as I got it only yesterday. Given the age of it, I expect to have a few more nitty griity issues before it is in good shape again.

So, thanks again for the offer of help. Let me know if you do have any parts for it.

[labjr]

Agreed. Since these are very old switches, no telling what effects they will have. I have seen 90% but even that was kind of rare. I guess I will have to hunt around or order from eBay.

Thanks for the tips.

I buy 91% at my local Walmart.

[tautech]

I forgot to mention....  don't neglect physical method of cleaning either.  I used to clean relay contact and rotary switches using business card stocks.  They are just rough enough to take the oxidation layer off without grinding off thin plating.  Carefully slide clean card stock between layers few times.  Worked especially well on relays.

If you need certain parts, you could always ask for one here.  Myself, I have a garage full of for-parts-only stuff.  Some of us will be glad to take parts off and send it to you.  I'm in US, and I once received a small part from Australia.  I've also given away spectrum analyzer parts.

What kind of Tek scope is it?

Ah! You are so generous! Let me give a little history. I posted elsewhere on EEVblog (https://www.eevblog.com/forum/repair/tektronix-465m-repair-210933/) about my 465M that died due to my accidentally leaving it overnight. Now, after spending almost close to $200 or so, I am still down with it as it seems like the HV transformer is possibly faulty.

In the meantime, I came across a 465 that I picked up yesterday. It seems like the Ch2 Input coupling switch is intermittent in making contact. I have still not opened it as I got it only yesterday. Given the age of it, I expect to have a few more nitty griity issues before it is in good shape again.

So, thanks again for the offer of help. Let me know if you do have any parts for it.

Hey you might want to look up med6753's posts about 465's, 475's and other Tek stuff he fixes.
Attenuator decks in these things are his speciality and it might even be worth dropping him a PM to point him to your threads.

There's plenty of examples of his work buried in the monster TE thread but check the first post as items of interest are linked there.

[labjr]

Good to see people still using old scopes. Still using a Hitachi 20MHz scope I bought 30 years ago for servicing audio equipment. I haven't felt the need to change. I've never tried a digital scope. Not sure but I feel like there would be a lag which would drive me crazy.

[andy3055]

When I was in my 30s I worked in Oman and had my Brit boss bring me a 20MHz Leader scope from UK that I took home with me to Sri Lanka. When I left the country about 25+ years back I sold it there. Funny I am trying to fix an old piece now!

[Gandalf_Sr]

If you use IPA (India Pale Ale), won't that gum up the contacts?

[tooki]

I wanted to let you know, IPA method isn't absolutely safe either.  IPA itself is relatively safe but what is often sold as IPA from regular stores are de-natured.  They are often mixed with numerous things including gasoline.  (often labeled as 70%)  You can try cleaning mirrors and let it dry.  You can often see oily residues.  So be careful.  In United States, if you look hard enough, you can find 90% kind.  99% is also available.  (even from places like Amazon!)  They are safer from de-naturing prospective.  I have only seen 100% from chemistry supply stores.  I have 70% and 99% and use them depending on what exactly I am doing.

I use De-oxit as well, but with some care.  Sometimes spray some into a container and use syringes (I have lots...  I am diabetic) to apply precisely.  De-oxit spray has very bad tendency to spray all over the place.  I had varying degree of success.  So far, I haven't had any case it caused damage.

There's really no 100% sure way of dealing with old switches.  I think, the best you can do is be familiar with various methods, and use small amount first.

While cheap IPA rubbing alcohol may have contaminants, it’s probably not denaturing agents, because IPA is itself a denaturing agent. Only ethanol (the alcohol we can drink) needs denaturing, which is the addition of a nondrinkable adulterant for tax purposes. IPA isn’t drinkable anyway, so it doesn’t need to be denatured.

According to various medical and addiction treatment websites, IPA rubbing alcohols supposedly contain Bitrex to make them unappealing for accidental ingestion, but I frankly don’t believe it, because Bitrex residue gets everywhere and you taste it on everything, even after thorough hand washing. (I’ve bought ethanol fireplace fuel with Bitrex before, not realizing it did, and I couldn’t use it for cleaning because it contaminated the whole damned house with Bitrex.) And for sure those sites are just plain wrong in talking about “denatured IPA”, per above.

[nctnico]

I forgot to mention....  don't neglect physical method of cleaning either.  I used to clean relay contact and rotary switches using business card stocks.  They are just rough enough to take the oxidation layer off without grinding off thin plating.  Carefully slide clean card stock between layers few times.  Worked especially well on relays.

That is a good one. Recently I used this method to get an AGP slot back into action.

[PaulAm]

Those contacts look like tiny gold plated tuning forks.  Over time they do pick up a little grime and the paper/IPA cleaning technique will work well.  Spraying contact cleaner is definitely the wrong way to go; it will leave residue that will screw up the attenuators.  Besides the attenuators, I had a bad AC/DC/Gnd coupling switch on one 465 that cleaned up nicely with the recommended technique.

It's something of a pain to do, but it's effective and will not make things worse (as long as you're careful)

In the US you can buy 91% at any drugstore and you can get 99% off of Amazon

[andy3055]

Again, thanks to all. I am surprised at how much of info this has brought forward. There are always thing to learn even when it seems like a very trivial question to ask!