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Filter Capacitor blown when fuse connected

philipshadow

Oct 29, 2020
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I have an asus laptop charger with a T3.15A 250v fuse. i checked the fuse with a multimeter but there was no continuity so i placed a wire across the fuse leads. Plugged in the charger and next thing i heard was a spark. checked the main filter capacitor rated at 400v and i found it blown. So I'm wondering if anyone can tell me if i did anything wrong.
I bridged the fuse(blue marker) and main filter capacitor blew up(red dots). It's a T3.15A 250v fuse
 

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Harald Kapp

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i placed a wire across the fuse leads.
That's a no no!
i checked the fuse with a multimeter but there was no continuity
Usually when a fuse blows there is a reason for it. The faulty capacitor may have been this reason. Or something else.
Replace the filter capacitor, insert a fuse. Then, before you connect to mains, check the input resistance (check for another short circuit). Use the light bulb current limiter method to prevent overcurrent when testing the power supply on mains.

Note: There are capacitors within the power supply circuit that can hold dangerously high voltages for some time after the power supply has been disconnected from mains. For your own safety make sure these capacitors are discharged to prevent risk of an electric shock.
 

philipshadow

Oct 29, 2020
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That's a no no!

Usually when a fuse blows there is a reason for it. The faulty capacitor may have been this reason. Or something else.
Replace the filter capacitor, insert a fuse. Then, before you connect to mains, check the input resistance (check for another short circuit). Use the light bulb current limiter method to prevent overcurrent when testing the power supply on mains.

Note: There are capacitors within the power supply circuit that can hold dangerously high voltages for some time after the power supply has been disconnected from mains. For your own safety make sure these capacitors are discharged to prevent risk of an electric shock.
okay, i will do just that
 

davenn

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the capacitor is not shorted though blown but its still reading when meter set to ohms

capacitors values are not read with a meter in Ohms range ... it should be a capacitance meter

but regardless of that sounds like you blew the cap completely
The bridge rectifier needs to be checked, it's probably blown and was probably the reason for the initial blowing of the fuse
this is very common in SMPS ( switch mode PSU's) that are in most plugpacks and other PSU's inside equipment
You will need to work your way through ALL the components between the power input and the switching transistor on the heatsink
 

philipshadow

Oct 29, 2020
36
Joined
Oct 29, 2020
Messages
36
capacitors values are not read with a meter in Ohms range ... it should be a capacitance meter

but regardless of that sounds like you blew the cap completely
The bridge rectifier needs to be checked, it's probably blown and was probably the reason for the initial blowing of the fuse
this is very common in SMPS ( switch mode PSU's) that are in most plugpacks and other PSU's inside equipment
You will need to work your way through ALL the components between the power input and the switching transistor on the heatsink
ohkay. i have seen a lot of youtube vidoes testing cap with an analog meter on ohm scale. But per what you are saying it implies that i may not get accurate reading when using the ohm scale. i need to get a capacitance meter. i am planning to buy
Richmeters Rm113D Ncv Digital Multimeter 6000 Counts Auto
 
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