: Knowledgebase

The Hookswitch Story from


Many manufacturers of electronic telephone equipment in the late 1970's and early 1980's decided that the cost, simplicity, and ease of installation on the printed circuit board would make the microswitch ideally suited to be used as the hookswitch on their phones, replacing costly spring type leaf switches that had been used since the beginning of telephones.

For cost and ease of installation, this worked out fine. But the engineers didn't think about the ramifications of their switch when used with DC talk battery (24 or 48VDC). Hookswitches that were used in phones (for AC audio, riding on top of a DC voltage) historically had a self wiping action. This means that each time the switch was turned on or off, there was a little "rubbing" action that tended to clean any oxidation or carbon left from a spark, from the area that would make electrical contact. The microswitches used in phones don't have that action, the contact points in the switch just touch in the same place every time they are activated without much "rubbing" action. Even a slightly bad connection on a phone line can cause static like crazy because there are constant small changes in the DC voltage. If you have a bad connection on the speakers on your stereo you don't have any static, but you maybe have a loss of volume, because there's no DC voltage - it's only AC (audio).

Phone men have been carrying burnishing tools since the beginning. They were used to clean the contacts on hookswitches, dials, line keys and relays. Historically, the best service came from contacts that had a little metal contact welded to each of the leafs on a switch, at right angles to each other. That's why the Western and Northern dials worked much better than the Stromberg dials (which were constructed poorly, like the microswitch).

Today, most manufacturers don't run voice through the hookswitch. They often use a microswitch or single pushbutton (tactile) type switch as the hookswitch. The switch simply tells the phone's microprocessor whether it's on or off-hook, and the micro takes care of switching voice paths. When the switch gets flakey it sends bad information to the micro, which dutifully hangs up the phone in the middle of the conversation or might not even go off-hook when the handset is lifted.


I was on the way to an emergency service call in the middle of the night in 1989 when I stopped at a convenience store for a bottle of pop. I ran into a repairman I had worked with who I hadn't seen for a while, Don Schuler. The first thing he said to me was "Hey, you got any of those TIE hookswitches?" On my drive downtown to the service call, I figured that if he didn't even say "Hi" before asking me for the switches, and I used the heck out of those switches myself (I had been ordering them from Japan for years), there must be a lot more people who could use them. I put a few ads in a few magazines and ordered a bunch of switches (they took 18 weeks to get from Japan so I had to buy a lot to make sure I wouldn't run out). They went over pretty well.

I spent years doing service calls in downtown Chicago. Sometimes, especially with a van, you can only get to within a few blocks of a call. It's hard (and expensive) to keep moving the car or truck, so I spent a lot of time walking (or taking cabs) around downtown Chicago. When electronic phones started getting popular around 1981 I found myself walking more and more - just to go get a new phone out of the truck (they weren't all that dependable back then).

It was time consuming because all of the old 1A2 5, 10 and 20 button phones had every button labeled with its phone number, and we did the same thing with the "new" electronic phones.

Well, besides for being too fat to keep walking up and back to my truck for new phones, it was a real pain swapping out the desis for all the lines (you'd think I would have lost weight doing all that walking but since there was a tobacco shop on the way into every building downtown, it was real easy to buy candy bars to keep up my energy... and fat!). I started opening up those phones to avoid the exercise and got pretty successful at fixing them with small parts I could carry in my bag, along with a soldering iron and some solder.

The manufacturers said that we'd void the warranty, but it started to make a real difference in the number of phones that were out for repair (I don't think it ever voided a warranty, and I know it was better than waiting a month or two to get the phones back from the manufacturer's repair depot). Lots of the things I learned along the way are now in our catalog, web site, and training videos.

I've always looked for the easier way to do things, and that included doing installations. Like everybody else (at the time), I spent years trying to fish a 1/8" tape through walls (wondering how many feet I'd have to feed in before I could grab it from the top) and trying to throw wires thru ceilings. When I found many of the tools in our catalog, I couldn't believe how much time I'd been wasting. I think you'll be impressed by these tools, too.


If there's more than one hookswitch, or more than one leaf to the hookswitch, the switch most likely to be causing static problems is the one controlling the DC talk voltage. If your phone is a single line phone and there's just one switch, that's probably the one. If your phone has two or more switches, touch each switch lightly, or try to touch an individual leaf with your spudger. You should hear a change in the static on the handset when you get to the right (bad) switch. If you listen in the handset and activate the switch, the audio will go away, but the selected line won't hang up, and you'll get the audio back when you release it.

You know you have the switch controlling the microprocessor when you operate it and the light for the line goes out (but you might still have sidetone in the handset). The microprocessor switch will be responsible for cut-offs while talking and can't go on or off-hook problems. This switch doesn't give much trouble since the microprocessor isn't affected by the slight voltage changes like the audio circuit is, the microprocessor is usually on or off-hook by circuit design. This switch can give you some pretty intermittent problems. I usually replace this switch when replacing the talk voltage switch automatically, just to save on a later service call. There really is no question as to whether the switch will go bad, just when it will go bad, and it's very difficult to diagnose an intermittent switch. I also replace all of the switches when I repair or refurbish a phone at the shop, including ALL used phones we sell.

You will find a third switch in some phones that have off-hook hands free intercom. This one usually gives the least trouble. Test it by placing a hands-free intercom call to that set, and touching the switch lightly while listening for slight noise or a lowering of volume. If this switch is bad, you may not be able to hear that phone when calling it on the intercom, or the intercom or ringing volume will be low. You can test any of the switches right on the customer's desk by just lightly touching the hookswitch (on the closed up phone), and looking for static changes or cut-offs.


Manufacturers like the idea of getting that phone in for repair after it's off warranty. They count on it. It's an annuity... $50 every few years.

I got a quote from a US switch manufacturer that claimed their microswitch switch won't have problems. The cost was VERY high, and I'm not sure I believe that their switch won't have the same problem two years out and can't afford to take the gamble.

Some manufacturers have gone to an optical type device for the hookswitch, where the hookswitch blocks off the (IR) light to the device and hangs up the phone. This works a lot better than the mechanical switch if everything is lined up correctly in the phone.

Other manufacturers have gone with a magnetic reed type hookswitch, which seems to work fine for quite a while.

Where a single switch is used for the hookswitch in an electronic phone, it controls the various sections of the phone through electronics, which is the most dependable way to do it. I don't know of any business phones being made today with more than one leaf / hookswitch.


The best investment I ever made in electronic tools was a vacuum operated electric solder sucker. They go for around $600 new and are almost impossible to find used. I take ours out to the customer's site when we take over maintenance on an old system that hasn't been serviced much. Since there are usually a whole slew of static problems, we save the customer money and ourselves headaches by replacing faulty hookswitches, handset cords and transmitters in mass. We just charge T&M and everybody is happy (customers change a funny shade of green when you tell them that you need to replace 15 phones...they really appreciate it when you can fix them right there). It would be suicide to take over the maintenance without clearing these problems first.

We sell a hand held vacuum combination Soldering/Desoldering Tool - with a tip that heats up. Plug it in, push the plunger down, and push the button to get one shot of vacuum (which is plenty). This unit is just a little bigger than an ordinary soldering pen and will fit right in with your other tools. With this tool, it's a quick and easy, ONE HANDED operation. This is an incredible tool!

If you use an electric solder sucker of any kind make sure you use the supplied thin rod to clean out the tube after each use, before it cools off! I speak from experience. The tube gets totally clogged with some kind of slag fairly easily and is usually impossible to clean out after that.

Our desoldering tool can also be used as a soldering pen, since the tip heats up. I carry the Soldering/Desoldering Tool with me all the time. If you use our tool, be sure to attach the included cleaning rod to the power cord, and USE IT EVERY TIME!

Most phones have a hookswitch soldered to the circuit board. It's a very frustrating experience to try to remove one of these switches without a solder sucker! To remove the switch, you'll have to break it into pieces with a pliers, so there is no mechanical connection between the three solder pins. Then you can apply the soldering pen to each pin and rip them out of the board. You'll probably damage a trace while you're doing it, but you'll get it out. Then clean out the hole as best you can and press the new switch into place.

Most will only fit in the correct position. You may have to apply the solder pen to get the pins into the holes. After the switch is mechanically inserted, apply the tip of your pen to both the PIN on the switch and the solder land around it. Flow a little bit of solder onto the PIN until it looks like the pin is almost covered. You should end up with a nice little pointy mound of solder, that looks like the original switch connection. A little practice will help.

If you get a big ball of solder, it's probably a cold solder joint, where the soldering pen didn't heat up the trace hot enough to let the solder flow between the pin and trace (and make a good connection). Apply your pen again for a few seconds. Don't use a soldering pen of more than 25 or 30 watts at the most. If you get it too hot, you'll probably destroy the circuit board in the process of replacing the switch.

DESOLDERING IS EASY... To use our solder sucker, place the hot opening over the pin, and WAIT for the solder to melt. If you don't see the solder melt, you'll just cool the solder when you activate the plunger. Two tries should work at most, letting the solder melt between each try. Use a pair of pliers to pull on the switch or actuator bar, and remove the switch. You might have to touch one of the pins with the hot tip while removing or inserting.