Comments on: Euronics Automatic Soap Dispenser Repair -2

By: Yogesh Panchal

Yogesh Panchal — Wed, 29 Jul 2026 10:06:46 +0000

Thanks! Philip,
That is not the case here, as I have already measured the voltages. You can see the LDO marked 'V3'(on Left side); electrolytic capacitors are connected to its input and output, correctly placed across the positive and negative lines.

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By: Philip

Philip — Wed, 29 Jul 2026 00:26:09 +0000

Mostly, the NPN switching transistor will have the middle pin connected to circuit positive power input. This case doesnt apply to what I see in one of your photos, because the power capacitor positive pins are not linked to the middle pin of the switching transistor. When the power switching transistor is of PNP type, which I suppose is what I see in one of the photos, then mostly, the grounds of the circuit may be positive. This makes the circuit to appear to be reversed. Open to rectification.

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By: Yogesh Panchal

Yogesh Panchal — Tue, 28 Jul 2026 17:04:01 +0000

In reply to AdamS.

AdamS,
When we connect the voltage input line to GND, it shorts out and damages the circuit.

Yes, when the switch lever is released or the cover is opened, the switch enters a 'floating state'; you have correctly understood the switch's operation in this regard. However, the input is certainly not connected to the ground.

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By: Yogesh Panchal

Yogesh Panchal — Tue, 28 Jul 2026 16:53:47 +0000

In reply to Mark J.

Thanks!MarkJ

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By: Yogesh Panchal

Yogesh Panchal — Tue, 28 Jul 2026 16:53:09 +0000

In reply to Anthony Paterson.

Anthony Paterson,
Thanks! for your view, when i traced the circuit i found output is
from pin no.1 that is Common Pin. & pin no.3 is Input, that is NO pin.

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By: Yogesh Panchal

Yogesh Panchal — Mon, 27 Jul 2026 08:19:41 +0000

Thank you! Albert
I didn't know anything either, until I opened up a switch lying in my pile of junk that was exactly the same type.Sharing it very soon.

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By: AdamS

AdamS — Mon, 27 Jul 2026 08:15:38 +0000

The switch is a changeover type, so when operated it connects the input of the LDO to the 6V power source to allow the dispenser to work, and when released it connects the input of the LDO to GND to stop it from operating. This is simply good practice to make sure that the LDO is properly switched off when not in use.

If the input is left floating, then there is a chance it could pick up stray voltages from nearby and behave unpredictably, and no one wants an unpredictable soap dispenser, especially when you're trying to refill it!

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By: Yogesh Panchal

Yogesh Panchal — Mon, 27 Jul 2026 08:13:15 +0000

In reply to Anthony Paterson.

Thanks! for your comment, Anthony Paterson

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By: Yogesh Panchal

Yogesh Panchal — Mon, 27 Jul 2026 08:10:02 +0000

In reply to Parasuraman S.

Thanks! for your Comment, Sir
I already had a faulty switch of this type lying around; when I opened it up to understand how it works, I discovered that it can be used in various ways. I will share the details very soon.

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By: Anthony Paterson

Anthony Paterson — Mon, 27 Jul 2026 06:14:36 +0000

In reply to Anthony Paterson.

OK back to your question:

Micro-switch (leaf-switch) has power applied when the cover is in place and removed when the cover is removed - so Battery IN and Battery OUT are connected to NO (Normally Open) contacts and the NC (Normally Closed) contacts are connected to ground. I presume grounding ensures the device is non-operational. The battery isn't shorted to the ground because they are never connected.

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