On/Off Switch: Why Six Pins?

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 ?

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

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

Cheers!

Reply to
c4urs11

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

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.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

Per Jeff Liebermann:

That would be the two middle contacts, right?

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Pete Cresswell
Reply to
(PeteCresswell)

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:

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.

Reply to
micky

Per micky:

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
Reply to
(PeteCresswell)

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

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

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 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.

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.

Reply to
micky

Per micky:

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  
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Reply to
Rheilly Phoull

Per micky:

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.

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Pete Cresswell
Reply to
(PeteCresswell)

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