Adjustable 12-24v laptop power supply blew a component, can anyone tell me what the component may have been?

Thread Starter

beachbouy

Joined Jan 4, 2019
6
P_20200407_210510.jpgs-l1600.jpg

I've been using this power supply for a few purposes. The one that killed it was as a 12v LED power source. The LED's lead shorted out and blew a fuse and this component on the power supply. I don't have enough experience with power supplies to guess which component was there, but I'm hoping to replace it and fix the circuit. I won't be using it for powering LEDs again... It was really for powering a Car stereo boombox project I'm working on.
Does anyone have one of these supplies? Or can anyone hazard an educated guess at what the component may have been?

Thanks for your help. :)
 

Dodgydave

Joined Jun 22, 2012
9,169
Looks like it's on the Input side , PCB marking says ' BS1' I would say it's a fuse or Mov.
Flash burns under the Bridge rectifier D2.
 

Thread Starter

beachbouy

Joined Jan 4, 2019
6
Looks like it's on the Input side , PCB marking says ' BS1' I would say it's a fuse or Mov.
Flash burns under the Bridge rectifier D2.
I first thought it could be a fuse, it definitely acted like one... But the amount of explosive debris from it seems to be too much for just a fuse? I could test the circuit with a fuse wire and see what happens...

I added a photo of the underside of the pcb with the Power in and the exploded component marked.
 

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dendad

Joined Feb 20, 2016
3,535
It may be a NTC surge limiter.
https://en.wikipedia.org/wiki/Thermistor
NTC.png
Try cleaning up the board to get rid of the debris, then wire a mains lamp across the device position.
Then, when you power up the supply (with no load), the lamp will limit the current. If the lamp glows brightly, there is further problems.
I would expect a blown bridge rectifier and/or switch transistor at least just by how well the part died.

Be very careful when working on this. It is very dangerous. A recommendation is to use an isolation transformer to help limit the danger a bit.
If you do not have an isolation transformer, a couple of identical transformers can be pressed into service, along with the series mains lamp to limit the power.
For example, mains :12VAC--->12VAC:mains. Then a 12V lamp could be connected between the transformers as the current limiting device.

The lamp is used to stop things blowing up if the power supply still has a short in it, as is most likely the case.
The lamp should flash when power is applied, then may glow dully. If it is bright, there is still a fault.
This is with no load on the supply.
 
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Thread Starter

beachbouy

Joined Jan 4, 2019
6
It may be a NTC surge limiter.
https://en.wikipedia.org/wiki/Thermistor
View attachment 204797
Try cleaning up the board to get rid of the debris, then wire a mains lamp across the device position.
Then, when you power up the supply (with no load), the lamp will limit the current. If the lamp glows brightly, there is further problems.
I would expect a blown bridge rectifier and/or switch transistor at least just by how well the part died.

Be very careful when working on this. It is very dangerous. A recommendation is to use an isolation transformer to help limit the danger a bit.
If you do not have an isolation transformer, a couple of identical transformers can be pressed into service, along with the series mains lamp to limit the power.
For example, mains :12VAC--->12VAC:mains. Then a 12V lamp could be connected between the transformers as the current limiting device.

The lamp is used to stop things blowing up if the power supply still has a short in it, as is most likely the case.
The lamp should flash when power is applied, then may glow dully. If it is bright, there is still a fault.
This is with no load on the supply.
I just did the test with the 12v lamp. It does stay bright after turning on 12v through the mains terminals. I used a PC power supply for the 12v but it is not likely 12VAC, it would be 12vDC. That could affect the test. The power supply has a 12vDC input for car usage, but I got no power through the lamp when I connected it. It does heat up the board through the 12vDC input though. The current draw must be huge on the 12vDC side because the spring in the cigarette socket plug has deformed from heat. I only powered it on for a few seconds.
 

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dendad

Joined Feb 20, 2016
3,535
Oops!
I forgot this was a 12V in, not mains.
Yes, it needs 12V DC, not AC. Sorry for the misdirection there.

Were you using the LED supply to drive this, or was the LED driven from this?
LED power supplies are often constant current devices so are not good to use for general power supply.
Also, can you please post a picture of the bottom of the board?
 

Thread Starter

beachbouy

Joined Jan 4, 2019
6
Oops!
I forgot this was a 12V in, not mains.
Yes, it needs 12V DC, not AC. Sorry for the misdirection there.

Were you using the LED supply to drive this, or was the LED driven from this?
LED power supplies are often constant current devices so are not good to use for general power supply.
Also, can you please post a picture of the bottom of the board?
I have a bank of 12v LEDs salvaged from a boat. I was using them as temporary lighting, using the power supply to power them. The wires on the LED leads were somehow shorted and that caused the damage to the power supply. It also tripped the house fuse.

This power supply can take both 240v mains and 12v from a car etc. That's one of the main reasons I chose it for my project. :) I tested both inputs. I attached the 12v from my PC power supply to the mains input with the 12v lamp attached. Then I tested the 12v input as well. The lamp was constantly lit from the mains connection, but not lit at all from the 12v input connector. It did heat up from the 12v input side though, but not the mains input.
 

Thread Starter

beachbouy

Joined Jan 4, 2019
6
I've been checking the continuity of the components on the board. They all have a level of continuity except the blue cap circled. I also noticed there was some heat in the circled areas. The board is discoloured so it must have been a good amount of heat. But would these guys be causing some of the issue?
 

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AlbertHall

Joined Jun 4, 2014
9,880
The blue thing with blue arrow is a varistor and it should read open circuit when tested with a multimeter.
The thing with the red arrow looks like a resistor from that angle. Can you give us a side view of it?
 
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