The Hookswitch Story, or
I Got Into This...
HOOKSWITCHES GO BAD?
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
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.
HOW DID I GET INTO THIS?
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
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.
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.
DO YOU FIND THE BAD HOOKSWITCH?
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 effected 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
MANUFACTURERS STILL USING HOOKSWITCHES THAT DON'T LAST?
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.
INSTALLING THE HOOKSWITCHES
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
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 that 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 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.