Dear all,

I’m reaching out for some advice regarding an issue with a Niko ( belgian brand) home automation touchscreen. This screen controls parts of our smart home system, but unfortunately, it has stopped functioning properly. The screen keeps cycling on and off repeatedly, making the device unusable. It wants to boot but the power keeps toggling.

The unit is powered by a 24V DC external power supply, which I have tested and confirmed to be working correctly. So the issue appears to be internal to the touchscreen itself.

I have some basic knowledge of electronics — still a beginner, but very eager to learn more.

After opening the touchscreen, I noticed that a choke 4R7 on the board becomes extremely hot, nearly glowing, and emits a burnt smell. I don’t have access to any schematics, which makes troubleshooting more difficult.

Here’s what I’ve observed:

• One side of the choke sits at 24V (from the power input).
• The other side is at 0V and is connected to the source of a MOSFET.

I’ve drawn a rough schematic of the components surrounding the choke not the whole board because it is complex board. However, there’s one surface-mount component I can’t identify. Its marking reads:

“942 LGSN N095”

It has 5 pins on the left and right sides, and 4 pins on the top and bottom, arranged in a square shape.

Would anyone be able to help identify this component? Or provide some insights into how this part of the circuit works — and what might be causing the choke to overheat and the power to cycle or some directions

Many thanks in advance!


Kenny

 

Looks like a power management IC. Could not find any datasheet, though.

 

Not much to go on there... I couldn't work out the bottom right of your diagram in blue pen; what component(s) does this refer to? The P-channel MOSFET in the circuit as drawn suggests its being used as a high-side power switch, but really need more detail.

I'd hazard a guess the mystery chip is some form of switched-mode power controller but its not a common one; too many pins for a start. Can you get a better idea of the markings? Try taking the picture at a low angle as you often can resolve markings better. A light wash with IPA can help too.

 

Not much to go on there... I couldn't work out the bottom right of your diagram in blue pen; what component(s) does this refer to? The P-channel MOSFET in the circuit as drawn suggests its being used as a high-side power switch, but really need more detail.

I'd hazard a guess the mystery chip is some form of switched-mode power controller but its not a common one; too many pins for a start. Can you get a better idea of the markings? Try taking the picture at a low angle as you often can resolve markings better. A light wash with IPA can help too.

Hello Irving,

Thank you for your reply.
The component drawn in blue is, in my opinion, some kind of feedback IC. As for the unknown component, I believe that’s its designation. I’ve tried viewing it from different angles and with a magnifying glass. I’m starting to think it might be a proprietary factory component.
I still have many measurements to take, but I’m trying to find out why the choke gets so hot. When I put it back, it starts to smolder.
28V also seems like a lot for such a choke.

Kind regards,


Kenny

 

Hello Irving,

Thank you for your reply.
The component drawn in blue is, in my opinion, some kind of feedback IC. As for the unknown component, I believe that’s its designation. I’ve tried viewing it from different angles and with a magnifying glass. I’m starting to think it might be a proprietary factory component.
I still have many measurements to take, but I’m trying to find out why the choke gets so hot. When I put it back, it starts to smolder.
28V also seems like a lot for such a choke.

Are talking about U3 or U9, its hard to get the details off either?. It's possible its a custom part, but very unlikely; it's very rare to use a custom component in a consumer product like this, although the package, if I understood.you correctly - 6 legs (1 missing) on each side plus 4 legs top and bottom - isn't a common one.

28v is irrelevant, the choke gets hot because too much current is being drawn through it due to a downstream short circuit - 90% likely its a shorted MOSFET or capacitor. Finding which is tricky though, especially if its a capacitor. Resistance measurements across the downstream supply rails won't tell you anything other than there is a low resistance, it can't identify where.

The way I'd solve this problem is to apply a low voltage, around 3v, +ve to the output side of the choke (choke removed) and -ve to the ground rail, from a current controlled power supply set to around 1Amp or so. A thermal camera will usually quickly identify the shorted component as a hot spot on the board.

Whereabouts are you?