How to test to see if a switch is working?

[vudoo]

Hey guys, I am new to flashlight and electronics in general and have a problem if anyone has the time to give me some assistance.

How do you go about testing a switch to see if it is okay? The flashlight I have has got a 3 mode switch. What setting do I use on the multimeter and exactly where do I probe? :thinking:

Thanks in advance!

 

[Marduke]

Set your DMM to Continuity and check the contacts of the switch as you cycle through.

 

[vudoo]

The switch has got 4 points coming out of it...so I set the DMM to continuity and touch the probes to any 2 points and then cycle through the 3 modes of the switch. By at least the third press of the switch I should hear a beep?

 

[Wiggle]

Use continuity mode to see which connection is the common for all 3. Turn switch off and test the battery spring with one probe and then try all 4 connections and only one should beep, that's the common. Now keep one probe on that common and alternate the switch on/off to see if each of the other connections shows continuity within 3 on/off cycles.

 

[von]

Check that each of the 3 identical legs connect to ground in sequence as you cycle the button. Ground is the fourth, shorter leg that is on the side of the black switch body that has a total of two legs (the short ground leg and one of the 3 longer, identical legs).

That short leg connects to a trace that goes to that little round solder blob in the corner of the board. If you turn over the board, you can see that that solder blob goes to a wire that runs into the flashlight body, no doubt to ground.

Thus, put your DMM in resistance mode or continuity mode. Put one probe on the short ground leg and the other probe on any of the other 3 identical legs. Cycle the switch until you get continuity. Leave the first probe on ground. move the second probe to the next switch leg. Cycle the switch and check for continuity. Do the same for the last identical switch leg.

The switch looks like it achieves its modes through a resistor network that you can see on the opposite side of the switch.

 

[vudoo]

Thanks wiggle and von for your explanations, they were spot on and I have tested the switch and it sems to be in working order.

The reasons why I asked for help is I purchased this torch and only after a week it died. From reading posts it seems that switches are one of the firsts things to test, hence my thread.

So what next?

I tested the two batteries and it came back with a reading of 8.02 volts. I placed the batteries back in the torch and used the multimeter to check if the power by placing a probe on the oter barrel of the torch and the other probe on the black wire from the torch going to the board (as seen in other pics). This came back with 8.02 volts so we were getting power.

What to test next I am unsure. Any suggestion? I have included pics of both sides of the circuit board.




http://s626.photobucket.com/albums/tt343/vudoo_01/?action=view&current=IMGP1470.jpg

 

[vudoo]

Arrrrrrrrrrrrr

This torch is going to drive me crazy. As I was screwing the torch together it worked! I only managed to go through 2 modes but I noticed the black wire had broken from the board but when I touched it to the metal base it worked and i had all 6 LED's.

So I took it apart, re-soldered the back wire on, put it back together and it didn't work....did I mention that I saw small spark when I was putting it together. Could I have shorted the drivers?

Okay, time to leave it for the night and to come back and have a look tomorrow before it gets thrown down the street

 

[vudoo]

Ok, so I think I know what is wrong with the torch. As I was playing with it and sliding the board back in the torch it suddenly turned on. I then discovered that there is a thin strip of metal along the side of the board and if I contacted this with the exposed torch barrel it turned on. Is this how the torch works by competing the circuit?

I then tried to wedge some foil in the groove to make a better contact but now trying to get the torch to work by contacting the barrel doesn't work anymore.

Does anyone have ever modified played around with a torch that works like this and has any ideas?

 

[zipplet]

Can you check for bad (dry) solder joints? If you see any, heat them briefly with a clean+tinned soldering iron to reflow them. Clean any contact points that touch the barrel with isopropyl or deoxit.

Edit: I'm saying the check for bad solder joints because one of the joints on the switch doesn't look like it flowed properly on the top side of the board. If you are going to do this be VERY CAREFUL about the surfacemount parts (they shouldn't need touching).

 

[Justin Case]

The switch looks like it achieves its modes through a resistor network that you can see on the opposite side of the switch.

Actually, I think that the modes are via 3 PT4115 PWM buck ICs. Is that driver board basically running 3 separate PT4115s, each with its own sense resistor network to set the output current? I think that might be how you get your 3 modes -- three PT4115s, three inductors, three pairs of diodes, three caps, three pairs of sense resistors (each with what looks like slightly different values to give different output currents, and each pair connected in parallel). Also, three pairs of output wires -- white/yellow, blue/green, and red/black.

That's a brute force method to implement 3 modes.

In fact, for sense resistor pairs at R1 and R2, it looks fairly clear that they connect to Pin 4 of their respective PT4115 ICs. That pin is the current sense pin. At R2, I see R33/R27. Can't read one of the resistors at R1. What is the marking on the one with the white dot on it? The visible resistor at R1 is R27. The third pair is only partially visible. I can see one marked R22. The red wire blocks the other.

Sense resistor network R2 should give nominally 667mA out. My guess is that R1 gives Low, R2 Medium, and R3 High mode.

The board also needs power. Where is Vin (Batt+) connected to the board? The two unconnected solder blobs at the two corners of the board on the end with the 3 pairs of colored wires seem odd. Are you sure that a wire didn't get broken off from one or both of those solder blobs? In fact, if you look at the traces on the board, the solder blob next to the black wire runs to Pin 2 of one of your PT4115 ICs. That pin is GND. Possibly, the other solder blob is for Vin. Or the black wire at the switch end is Vin (not GND) and the color code choice for the wire was poorly done. Where does that black wire go? Does it connect to the flashlight body, to some other switch, to Batt+, something else?

Can you take another photo of the component side, this time showing the complete board? Your photos above cut off part of the board. What flashlight is this? How many LEDs? What type -- Cree XR-E, Seoul P4, MC-E, P7,...? It would also help to get a complete picture of the system. Photos up the bore of the light at each end of the driver board might help in terms of understanding what wires are going where.

 

[vudoo]

The torch is a Romisen RC-T6. This is one of my first torches before
discovering CPF. I could have easily purchased another form DX for $60
but I really want to see if I can fix this thing. It was awesome the first
few times I used it.

I have gone through the board and re-soldered all the wires to eliminate
the problem of having a dry joint.

From what I can see, the way the torch works is the + come through the
black wire and negative is achieved by running along the inside of the torch barrel and torches/connects to the side of the board or the 2 solder blobs at the end of the wires. For more detailed pics of the torch un-assembled please click here.

http://www.candlepowerforums.com/vb/showthread.php?t=210134&highlight=romisen

I really think that the issue is that the circuit is not completing as when I
play around and try to assemble the torch it momentarily comes on.

What do you guys think?

 

[Justin Case]

In your photos of the driver, a red wire is missing. This wire connects the two solder blobs at the left and right corners of the circuit board at the end of the board opposite the switch. This is probably your ground. The solder blobs most likely make physical contact with the slot machined into the flashlight tube, into which the driver slides. So, #1 make sure that the solder blobs contact the metal surfaces in those slots, and #2 attach a wire to connect the two solder blobs.

The black wire coming out of the tube and going to the circuit board is probably Batt+ (unless the light is one of those odd ones where you put the cells in backwards -- in that case, the black wire is ground and the solder blob contacts above are Batt+).

The light shown in the link that you referenced is more brute force than I thought. The six LEDs are wired in 3 pairs, with each pair driven by one of the three driver circuits on the board. Thus, low mode is achieved by running just one pair of LEDs. Medium mode runs two pairs. High mode runs all three pairs.

The LEDs in each pair are wired in series. Thus, to run the buck driver in regulation, you need Vbatt of probably at least 6V-7V (depending on the exact drive current and thus the exact Vf for the LEDs).

That light is slightly different from yours, however. Yours seems to show different sense resistor values for the three sets of buck drivers on the circuit board. The one in the link your provided shows three identical sense resistors (R270).