Help me understand this circuit.

[TheMightyGoat]

Here's the deal. I bought a PALight. It has four modes: Glow, low, high, strobe. No off. The "glow" mode is as close to off as it gets. In this mode it emits a tiny bit of light at low energy consumption (supposedly will last two years) so as to make it difficult for the user to lose the flashlight.

Well I want it to turn off. I've been looking at the circuit board that regulates the different modes. I figure if I just interrupt the circuit that delivers the constant low power for the glow feature, the switch position which was previously "glow" will then be "off" - provided I can do that without affecting any of the other circuits.

I can't figure out which circuit to interrupt, though. Here is a picture of the circuit board (I can't get to the back of it without destroying the light). Initially I thought that Q2 on that board was regulating the current for the glow mode, as I noticed with a multimeter that a constant low current passes through this point, but current to the other three similar fixtures (D1, D2, Q1) doesn't change as the other modes are selected. The switch is in the middle at the bottom.

Another thing that may be relevant. I was trying to figure out to what extent the switch is mechanical. I noticed that if I remove the battery from the light with it in "glow" mode and press the switch with no power to the light, then replace the battery, it will not have changed from glow mode. However, with the battery replaced and I advance from "glow" to "low", then remove the battery and replace it, the light will still be in "low" mode. Repeating the process starting from low, the light will advance from "low" to "high" with the battery removed. Then again, it will not do the same from "high" to "strobe" without power. And again, it will advance from "strobe" back to "glow" without power.

Any thoughts?

 

[Gunner12]

I think there is a way to turn off glow mode without touching the circuit board, but I don't recall how.

:welcome:

 

[TheMightyGoat]

I think there is a way to turn off glow mode without touching the circuit board, but I don't recall how.

:welcome:

That's true for the Safelight. I don't think it is for the PALight.

 

[Gunner12]

Wow, I have to learn to read.

Sorry, no suggestions from me then.

 

[CampingLED]

Not familiar with the chips, but looking at the numerous resistors on the circuit board your answer may be there. Measure the voltage drop over the resistors in the various modes (voltage drop will also equal a current flow). If you find one that only has a voltage drop in low mode you could try to disconnect it (open circuit) and hopefully not impact on any other modes. Just my thoughts, but please don't blame me if it goes

 

[chimo]

The easiest way would be to cut one of the battery traces and insert a switch, however, this is a two sided board and you mention that you cannot get to the other side to verify if there are addition bettery traces there.

I suppose you could just remove it from the battery.

The ICs are a quad NAND Schmitt trigger and a quad Flip-Flop.

Wonder what that empty switch location is for?

 

[warlord]

I don't know if this applies to your version but did you try this:

To deactivate glow mode: press and hold down the switch for 2 seconds while in glow mode

It may not apply but I'd at least try it.

 

[TheMightyGoat]

I don't know if this applies to your version but did you try this:

To deactivate glow mode: press and hold down the switch for 2 seconds while in glow mode

It may not apply but I'd at least try it.

I tried it.

 

[warlord]

I would go through the circuit with a multimeter and test which resistors are being used in each mode. Look for a resistor that is only being used in 'glow' mode and remove it.