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Field Expedient Method to Fix Switches

(WY3X) on March 12, 2009
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Field Expedient Method to Repair Sealed Switches

I inherited a Yaesu FRG-7700 from one of my elmers (W3VT, Bob Cheek, ). It had a problem with the MODE switch when I received it, and as time passed, the problem got worse. Every time I wanted to listed to it, I had to fiddle with the switch to get reception. One Sunday, the problem got so bad, I decided to do something about it.

Assuming the mode switch was an open frame switch, I grabbed my can of De-Ox-Id and opened the cabinet. I always lay out a soft white towel when working on radios. It helps to find dropped small parts, and keeps the radio from getting any new scratches. (Don't have any De-Ox-Id? You should keep a can of this in your radio tool kit. It has all sorts of uses! It's GC part number 19-1906.)

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Upon opening the cabinet and getting to the part, I discovered that it was a sealed unit! It was completely closed, and riveted shut! I began thinking- what might this part look like inside? It had to have an ordinary wafer switch inside, I thought, I just need to discover a way to get this De-Ox-Id inside. Hmmm….

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I found a spot on the perimeter that had no contacts, and considered drilling a hole in the side of the switch to get access. The switch case was plastic, so using an ordinary drill was not an option. A regular drill bit will sometimes catch and pull itself into whatever you're drilling, sometimes destroying whatever it comes into contact with. It will also sometimes act as a wedge, and could possibly crack the plastic case. Knowing the age of this radio, and fully realizing that if I destroyed this part, I knew I needed something other than a drill bit to make the hole.

Enter a Dremel tool and a dental bit! These bits are available at many hamfests, and come in handy for all sorts of jobs! I found a very tiny one that would make a hole just large enough to insert the spritz straw that De-Ox-Id comes with. Setting the Dremel tool on as low a speed as it would go, I cut a tiny hole in the side of the switch. Afterwards, a few quick spritzes in the hole while rotating the switch through it's range of motion quickly cleaned all the contacts.

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After spritzing the inside of the switch, I then used a drinking straw to concentrate my breath and dry up any liquid left behind, being careful not to deposit too much moisture from my breath. A can of dry compressed air would work better, but I didn't happen to have one. Rotate the switch while blowing air into it to aid in cleaning the contacts even more. De-Ox-Id is designed to be left on as a contact lubricant, and need not be removed.

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I hope this method helps you save a radio that otherwise might end up in the trash pile because of obsolete parts! -KR4WM

Member Comments:
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Field Expedient Method to Fix Switches  
by N6AJR on March 12, 2009 Mail this to a friend!
great tip, A lot of the time when a switch or pot gets intermittent, I grab it and give it ten ot 20 good twists to "clean" the contacts a bit, this works on a piece that has set a long time and made a flat spot on the potentiometer or such.
 
RE: Field Expedient Method to Fix Switches  
by N2EIK on March 13, 2009 Mail this to a friend!
I have used this method many times repairing stereos. It does work great and de-ox works very good too. I also keep a small bottle of the red de-ox liquid. The stuff costs more than plutonium but a little bottle will last for years.
 
Field Expedient Method to Fix Switches  
by K0UA on March 13, 2009 Mail this to a friend!
Great article, we need more just like it.
 
RE: Field Expedient Method to Fix Switches  
by K0BG on March 13, 2009 Mail this to a friend!
The switch is very similar to Grayhill's stacked, rotary switch line. If you know the configuration of the switch, you can buy individual sections, and built up a switch which will work. You can't do it every time, but if you have an old radio you're trying to fix or restore, it pays to remember this avenue.

Alan, KBG
www.k0bg.com
 
RE: Field Expedient Method to Fix Switches  
by K4JJL on March 13, 2009 Mail this to a friend!
I changed out a switch like this one in my old Icom 730. It was a nightmare. I "thought" I was placing the wires in exactly the same places, but I ended up miswiring it an blowing out 2 voltage regulators (required faceplate removal to fix regulators). Took a couple weeks to trace the wires and fix it.

I'll try this method next time.
 
RE: Field Expedient Method to Fix Switches  
by K9MHZ on March 13, 2009 Mail this to a friend!
A little off topic, but maybe it will help someone.....when cleaning relay contacts, especially in boatanchors and amplifiers where the relay contacts would have pitted from arcing, be careful when using the paper sliding method through them. The relay contacts tend to take a hook shape over time, which will scrape the paper as you slide it through. There's a good chance you'll insulate the contacts without knowing it, and your rig/amp may then seem like it died.

Deoxit is really good stuff.

Good post!

Brad
K9MHZ
 
Field Expedient Method to Fix Switches  
by KE4ZHN on March 13, 2009 Mail this to a friend!
It might be a good idea to put a small piece of scotch tape over the hole after you do this to prevent dirt from migrating back into the switch.
 
Field Expedient Method to Fix Switches  
by K0UC on March 13, 2009 Mail this to a friend!
This an excellent article. As my 'vintage 70's radios' age, this sort of thing will become very pertinent. Thanks for taking time to post it.
73
Brady
 
RE: Field Expedient Method to Fix Switches  
by KG4TKC on March 14, 2009 Mail this to a friend!
Excellent article KR4WM! Nice pictures to go with it. The Dremel tool with a dental bit was a fine idea,I will remember that one,,:) Thanks for taking the time to share with us. I have to also add that Deoxit is a fine product to have on the shack bench. KG4TKC
 
Field Expedient Method to Fix Switches  
by K1CJS on March 14, 2009 Mail this to a friend!
Nice tip! I may add that a wrap of electrical tape just may stand up better than scotch tape for 'plugging' the hole.
 
RE: Field Expedient Method to Fix Switches  
by K7PEH on March 14, 2009 Mail this to a friend!
So, why are these switches sealed like this?
 
Field Expedient Method to Fix Switches  
by AF6G on March 14, 2009 Mail this to a friend!
Great article. Kind of like the "Hints and Kinks" from QST of years past. We need more articles on eHam like this.
 
RE: Field Expedient Method to Fix Switches  
by KE5CYB on March 14, 2009 Mail this to a friend!
Excellent article! This is exactly the type of good ole HE (Ham Engineering) we need to see on eHam. Keep 'em coming.
 
RE: Field Expedient Method to Fix Switches  
by K6LHA on March 15, 2009 Mail this to a friend!
K7PCH posed the question "why are switches sealed like this?" on 14 Mar 09:

The most obvious answer is to keep any sort of garbage out of the contact area, such as stray clippings of wire or other metal OUT. The other answers are subtle and have to do with the design of the rotary switch and the design of the equipment that uses it. To expand on the latter requires some explanation of the old, 'standard' rotary switch, such as the Centralab rotary switch line with (once upon a time) having wafers with 2 to 11 positions, 1 to 4 poles, shorting contacts or break-before-make contacts. All sorts of choices and they came in paper-phenolic dielectric or ceramic dielectric. All of those old, 'standard' switches had contacts fully open, unprotected and one could not stack wafers together, only through long pairs of screws with wafer-separation insulating tubes.

More-innovating manufacturers such as CTS (one example, formerly Chicago Telephone Supply corporate name) took on the thin-wafer, connection lugs in-line, sealed or semi-sealed wafer design after WWII. CTS was semi-sealed in that it had some relief holes in the rotor area, something like 10 to 20 percent (if memory serves). Instead of using eyelets to fasten stator contacts to the outer dielectric part of a switch wafer, the sealed switch makers molded-in the stator contact set and the exterior wire connection lugs with the main switch wafer body. After molding it was a very integral unit, quite 'one-piece.' Rotor contacts were in their own dielectric carrier (CTS stock design had clear plastic, main body grey). End result for any stack of wafers in any rotary switch assembly was a compact although flexible design that suited many applications, particularly range and function switches in the semiconductor test set plug-ins that I designed at Birtcher Instrument Division in Monterey Park, CA. With repeatable, flat-plane contact arrangements, they were just a tiny bit better suited for higher frequencies than the old, standard, all-open-to-the-elements designs that began in the 1930s. Grayhill (among a few others) survived the eventual demise of multi-wafer rotary switch combinations of olden times; Grayhill's design is very sealed.

The thinner, sealed rotary switch is better for piece-work production assembly in that all connections are in the same plane as the wafer, wires can hook though them a bit better than on old-design angled lugs. There are fewer errors from metal particle shorting that require extra labor-time repair on a production line. Setup costs for the old-design rotors were still less than for new, sealed-wafer designs but only 10 to 20 percent less. That could be amortized and offset by less labor for production line rework, something dear to manager's hearts. :-)

I should note that range and function switch subassemblies could be obtained with nice, compact mounting of resistors or capacitors between wafers and took the least time to design than the old, standard rotaries which required juggling wafer-separation tube sections made in odd fraction, limited sizes (for ceramic wafers). The sealed switch units looked better to anyone investigating the insides of a product in detail, another selling-point to customers. Silver-plating of rotary switch contacts were much more prone to long-term oxidation than the sealed-switch designs. For that matter, rotary switch customers should have specified other platings such as rhodium flash over another metal over the base contact metal. Also, the contacts of the sealed switch variety could be done with less metal-against-metal wear of the old, standard eyeletted or staked-together switches. That reduced long-term wear.

Nowadays the architecture of electronics has changed considerably. Radios that cover all of HF don't need rotary switches, their internal heterodyning methods obviate 'range switches.' Low-power bandswitches, if required by receivers, can be done with PIN diode electronics switches (FAR longer operating life). Lower-power contact relays are now abundant; see such as the Omron lines (plural) that are used in lower-power automotive applications. Automatic antenna tuners switch their banks of L and C by relays in a binary tree, coils driven by microprocessor control lines directly; coil powers are down to less than 100 mW. All of those applications cost less to make, drops the over-the-counter prices. A few old-style rotary switch parts are still available (once one finishes searching for one) but their piece prices are practically astronomical now.

OK, probably more than you wanted to know, but that is how it is. :-)

73, Len AF6AY
 
Aplogy tendered to K7PEH  
by K6LHA on March 16, 2009 Mail this to a friend!
I made a typo in attributing your question to 'K7PCH' and want to note that. My apologies.

Len, AF6AY
 
Field Expedient Method to Fix Switches  
by K1DA on March 16, 2009 Mail this to a friend!
REAL DEOXIT is made by Caig Labs, not CG. The real thing works best.
 
Field Expedient Method to Fix Switches  
by K1DA on March 16, 2009 Mail this to a friend!
I would also suggest going to a hobby shop and picking up a "pin vise" which can hold the very small drill bits sold for hobby use. More control if you are turning the bit yourself rather than using a big bulky motor powered device. A lot better, even, than my very small battery powered Dremel.
 
RE: Aplogy tendered to K7PEH  
by K7PEH on March 16, 2009 Mail this to a friend!
>>>
I made a typo in attributing your question to 'K7PCH' and want to note that. My apologies.

Len, AF6AY
<<<

No problem-o Len --- I appreciated your answer just as much with a small error in my call sign.

phil, K7PEH (actually, my initials so it is easier for me to remember)
 
Details on similarly-named contact cleaners  
by KT8K on March 17, 2009 Mail this to a friend!
Actually "De-Ox-Id" is a spray contact cleaner from electronic-related products supplier General Cement, is relatively inexpensive, and was once widely available among electronic parts sellers (most long gone). "De-Ox-It", on the other hand, is a high-end contact cleaner from CAIG. I have used both, and far prefer the CAIG products, but the GC cleaner does work. I just found that in some applications I had to be ready to re-apply it every 6-12 months. The CAIG product, while much more expensive, has never required me to re-apply it.
That's just my experience - nothing scientific about it - but I thought I'd fill in as K1DA seemed confused by the *very* similar product names.
Best rx & 73 to all de kt8k - Tim
 
RE: contact cleaners  
by K6LHA on March 20, 2009 Mail this to a friend!
KT8K posted on March 17, 2009:

"Actually "De-Ox-Id" is a spray contact cleaner from electronic-related products supplier General Cement, is relatively inexpensive, and was once widely available among electronic parts sellers (most long gone). "De-Ox-It", on the other hand, is a high-end contact cleaner from CAIG. I have used both, and far prefer the CAIG products, but the GC cleaner does work. I just found that in some applications I had to be ready to re-apply it every 6-12 months. The CAIG product, while much more expensive, has never required me to re-apply it."

I will agree with you, Tim, and have to note I grew up in the town where GC began. :-)

I used GC "contact cleaner" (name before the better commercial product came out) decades ago as an ardent hobbyinst and once-in-awhile part-time TV repair money-grubber. It was never formulated for 'long life' by the original chemical formulator (GC repackages a lot of things buying other companies' products in bulk). Its 'cleaning action' is primarily as a lubricant which, accompanied by an unpleasant odor, make the user THINK they are cleaning something.

On the other hand, from listening to a lot of folks in the entertainment business, primarily in 'post-production houses' in/around Los Angeles (over 300 last I heard), the CAIG products are long-lived with little need to re-apply their cleaners. To explain, older audio mixing consoles would have multiple-contact continuously-rotating (no mechanical indexing) 'potentiometers' carrying low-level audio.* Contact noise would be readily apparent if it was there. Post-production companies in a very competitive market couldn't afford to spend time 'fixing' noisy audio (later video) electronics. While the ancient (pre-WWII) rotary gain controls were nearly always sealed, the in-line 'slider' types were more open by their control tab slot (seals would eventually wear out before any contacts got bad). Folks around here in the entertainment capital of the world don't want to fool with 'mouse milk' products (except for the Disney company) that don't do their job. That's where CAIG and a few of their contemporaries stepped in with superior products.

* Those old Pro gain controls are very-limited-application 'potentiometers' originated in motion picture sound production early in the 1930s, spread quickly to audio broadcasting and phonograph disc recording to become a mainstay of 'gain riders' controlling audio. They have fixed resistors and lots of multiple taps, each tap having multiple contacts on rotors, with the resistors usually in Tee configurations for low impedances (typically 600 Ohm in/out), contact metal alloys picked for a compromise of minimum oxidation and wear. They would usually outlast the employment time of any gain-rider using them. Costly, a single replacement gain control would cost more than a new retail-price Hallicrafters S-38 back when Halligan's company introduced that receiver. Some of those same gain controls are still alive and working today in broadcasting and recording. S-38s are now 'operating' on e-bay.
................
GC products were once 'popular' (their name known) with hobbyists because they were relatively CHEAP and distributed through 'radio parts stores' and had lots of advertising in radio/TV magazines. Only a few GC products are, in my opinion, worth their price: A fine design wire stripper flawed only by inattention to quality control on a spring (I had two, both with the same spring break failure); Corona dope, fine for 15 KV and up lines but displaced by much lower voltage display technology; 'Strip-X' one of the easiest-to-use magnet wire de-enamelizers ever, not permitted to be shipped out-of-state by later 'health laws' on chemical formulations that were supposedly terribly Terribly toxic, deadly Deadly Dangerous for shippers. Well, their old alignment tools are okay...those are inert but they don't get a lot of use either. Sort of like Greenlee chassis punches (another company from my home town). :-)

73, Len AF6AY

 
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