On/Off Switch: Why Six Pins?

[(PeteCresswell)]

Automobile dash cam failed.

I am pretty sure it's the On/Off switch, so the workaround will be to
hard-wire the thing to "On".... No loss because it's always turned "On"
anyhow.

But this thing is just "On" and "Off" - yet I see six pins under it.

In the pic below, you can just see the little green slider on the other
side of the board. Slider to the right = "On".

I come away from looking the pic thinking that the two leftmost pins are
not used at all (no etched connections visible), the two righmost pins
are clearly used (visible etched connection going somewhere else on the
board), but am not sure about the middle pins.

Before I unsolder this thing and just jump the two rightmost pins - and
maybe mess something up.... can anybody comment on the possible roles of
the other pins ?

https://picasaweb.google.com/108149798664924808733/Misc#6204033735361530914

If somebody asks, I will go back and try to get a clearer pic.
--
Pete Cresswell

 

[c4urs11]

On Sat, 10 Oct 2015 11:06:13 -0400, (PeteCresswell) wrote:

.... can anybody comment on the possible roles of
the other pins ?

Looks like a common DPDT switch ("Dual Pole, Dual Throw").
Google "DPDT" and you'll find all you need to know, maybe more

Cheers!

 

[Jeff Liebermann]

On Sat, 10 Oct 2015 11:06:13 -0400, "(PeteCresswell)" <x@y.Invalid>
wrote:

>Before I unsolder this thing and just jump the two rightmost pins

The "on" contact traces are already jumpered on the PCB. Look at your
photo.

- and
maybe mess something up.... can anybody comment on the possible roles of
the other pins ?

https://picasaweb.google.com/108149798664924808733/Misc#6204033735361530914

DPDT switches are commonly used for power on/off because with 6 pins,
the switch is solidly mounted to the PCB. It will not wiggle side to
side as it would if it were a SPDT (3 pins). Also, manufactories like
to use as many of the same parts as possible. It doesn't make much
sense to inventory SPST, SPDT, DPST, and DPDT switches, when a DPDT
will do the job of all of these. Lastly, if there is any inrush
current when turning the device on, distributing the current through
two paths saves some wear and tear (or arcing) on the contacts.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[(PeteCresswell)]

Per Jeff Liebermann:

The "on" contact traces are already jumpered on the PCB. Look at your
photo.

That would be the two middle contacts, right?
--
Pete Cresswell

 

[micky]

In sci.electronics.repair, on Sat, 10 Oct 2015 16:15:23 -0400,
"(PeteCresswell)" <x@y.Invalid> wrote:

Per Jeff Liebermann:
The "on" contact traces are already jumpered on the PCB. Look at your
photo.

That would be the two middle contacts, right?

The two middle ones are connected and the two to the right are
connected, afaict. So both poles of the switch turn on simultaneously,
or very very very nearly so.

What problem is the switch causing? Are you not sure it's on when
it's supposed to be on? Remove the power and measure the voltage
between the middle two contacts and the right ones.

It should be zero. If it's zero, you can then measure the resistance
between them, the middle two contacts and the right ones. It should
be about zero when the switch is closed and very high when the switch is
open. If it's not, post back. I don't know enough about
circuitry to insist that all my expected conditions be true. For
example, iirc some switches have a capacitor across them, to reduce
sparking I think. If the capacitor were to short, the resistance even
when open would be low.


From the first post:
>Before I unsolder this thing and just jump the two rightmost pins - and

Even if in another situation you needed to jump the two pins, I'd see no
need to unsolder the switch. Well, unless you were afraid the presence
of the switch woudl mislead someone, or you needed to take it, and not
just its dimensions, with you to buy a new one.

maybe mess something up.... can anybody comment on the possible roles of
the other pins ?

 

[(PeteCresswell)]

Per micky:

What problem is the switch causing? Are you not sure it's on when
it's supposed to be on? Remove the power and measure the voltage
between the middle two contacts and the right ones.

This will be awhile. I need to find some reliable probes for my
el-cheapo voltmeter.... the ones I am trying to use are not getting it
for such small targets as the pins on the bottom of that board.

The device in question (a automobile dashcam) is supposed to start up
automagically when 12 v is fed to it and the switch is on.

The switch is always on.

But starting a few weeks ago, it was coming on sometimes, not coming on
other times.... and now it is never coming on.

I *think* am getting 12v on the power source... so my guess was that the
switch had failed.

Now I am not so sure about the power source because of my issues with
the meter and it's probes.....

Stay tuned...
--
Pete Cresswell

 

[micky]

In sci.electronics.repair, on Sat, 10 Oct 2015 18:02:26 -0400,
"(PeteCresswell)" <x@y.Invalid> wrote:

Per micky:
What problem is the switch causing? Are you not sure it's on when
it's supposed to be on? Remove the power and measure the voltage
between the middle two contacts and the right ones.

This will be awhile.

I know that feeling. Some of my projects have lead times of 5 or 10
years.

I need to find some reliable probes for my
el-cheapo voltmeter.... the ones I am trying to use are not getting it
for such small targets as the pins on the bottom of that board.

In the picture, the board is leaning against a keyboard, so I can tell
how big it is, and ...any probes should work, unless your hand shakes.

I used to make, and now I buy, jumper wires with alligator clips on each
end. A package of 10 light weight, 18 gauge, is about 3 dollars.
Heavy weight, 16? I havent' seen lately but I rarely need that.

And I clip one end of the jumper to the black probe, and the other end
to what looks like a ground in the device. Or a leed or spike of solder
that can be clipped to. Especially important with hot circuits so I
can concentrate on where the red probe goes.

But I don't think that would actually work here

The device in question (a automobile dashcam) is supposed to start up
automagically when 12 v is fed to it and the switch is on.

So at most, if unplugged, not especially this device, it could have less
than 12 volts in a capacitor and it can't hurt you, but others here
could tell you if a 12 volt cap could discharge through an ohmmeter and
damage it. But I'm sure there are no big caps on this board.

The switch is always on.

But starting a few weeks ago, it was coming on sometimes, not coming on
other times.... and now it is never coming on.

I *think* am getting 12v on the power source... so my guess was that the
switch had failed.

The switch itself, Not especially likely IME. For one thing, the
switch is two pole, like two parallel switches. They'd both have to
fail.

Before you do anything more, look for cold solder joints or solder that
has cracked. First at the switch. If there is a crack around a pin,
between the pin and the solder, especially if it goes all the way
around, that's very bad. And sometimes the solder is stuck to the pin
but cracked in the middle of the solder, If there's a trace underneath,
I guess that's not so bad. But I'd remelt and resolder anything that
looks like that. Especially on a switch, which is not a transistor.

But the advantage of using a meter from the beginning is that if you
found the solder at the switch was bad, and now it's good, you know you
fixed some, likely all of the problem. If you resolder now, measure
only afterwards, you won't know if you fixed anything.

If you're bad at soldering, I'd avoid resoldering transistor leads, for
fear of damaging the transistor with heat. You want to melt the solder
quickly and quickly remove the iron so it cools. If you're good at all
this

I hate to skip using a meter. It answers questions. But if I were
McGiver and my life depended on it, and all I had was a ball of twine
and a soldering iron, I'd skip the meter for now and solder a little
piece of wire across the bottom two connectors. The bottom right has a
trace. Not sure which of the left points have one. Maybe the top. If
the top, make the wire twice as long and bend it so it goes to the top
left too.

Now I am not so sure about the power source because of my issues with
the meter and it's probes.....

Stay tuned...

Harbor Freight has good enough meters for 5 dollars. Lowes and Home
Depot have them for under 20. I've lost track of Radio Shack though I
know it still has 1700 stores open, though their webpage doesn't have a
catalog yet. Plus if you have a meter and probes now, I can't
imagine what is wrong with the probes. On a low voltage like that, and
disconnected to boot, so you can't hurt yourself, you don't even need
probes. You could just use the wire, stipped back 1/8" and use the
wires at the end.

 

[Rheilly Phoull]

"(PeteCresswell)" wrote in message
news:bh2j1bdmlv5ju5djcqgb5bloddtv8m12ib@4ax.com...

Per micky:

What problem is the switch causing? Are you not sure it's on when
it's supposed to be on? Remove the power and measure the voltage
between the middle two contacts and the right ones.

This will be awhile. I need to find some reliable probes for my
el-cheapo voltmeter.... the ones I am trying to use are not getting it
for such small targets as the pins on the bottom of that board.

The device in question (a automobile dashcam) is supposed to start up
automagically when 12 v is fed to it and the switch is on.

The switch is always on.

But starting a few weeks ago, it was coming on sometimes, not coming on
other times.... and now it is never coming on.

I *think* am getting 12v on the power source... so my guess was that the
switch had failed.

Now I am not so sure about the power source because of my issues with
the meter and it's probes.....

Stay tuned...
--
Pete Cresswell

For the probes use a file and sharpen the ends to a fine point. This helps
for small points and pierces any coatings too.

 

[(PeteCresswell)]

Per micky:

So at most, if unplugged, not especially this device, it could have less
than 12 volts in a capacitor and it can't hurt you, but others here
could tell you if a 12 volt cap could discharge through an ohmmeter and
damage it. But I'm sure there are no big caps on this board.

I'll start in on the cold/cracked joint inspection next.

I have no clue what constitutes a big cap but, FWIW, this cam is
designed to run for a certain period of time after the 12v external
power has been removed - and they do that by using 2 capacitors instead
of a rechargeable battery. Each capacitor is about 3/4" long and 5/16"
in diameter. This is supposedly a higher-end feature because the caps
will not wear out like rechargeable batteries will.
--
Pete Cresswell