220VAC to 12VDC Troubleshooting

Thread Starter

snaggletooth

Joined Oct 22, 2020
5
Hey guys, this is my first time posting so sorry for any inconvenience related to that.

So i have this old coffee machine, brought to me by a friend. Doesn't work, doesn't light up, does nothing. I suspected a transformator issue so i stripped it down(was a painful proccess) then i gave 12vdc to machine via an external source. It lighted up.

I was sure then so I disassembled it, took the transforming circuit out. Found a faulty(checked with a make-shift Arduino capacitor checker which i made myself) 220 uf capacitor, changed it. Found a dead resistor(2.2 ohm 1w metal film) acting as a fuse. Changed it too. Then i was pretty sure it was going to light up. Plugged it in and boom. There goes my resistor(fuse) again. So I'm all out of ideas. Please don't hesitate to ask further questions and recommend stuff. Thanks in advance.
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MrChips

Joined Oct 2, 2009
22,097
So the coffee machine works from an external 12VDC supply.
Disconnect the original supply from the machine and test it on its own, firstly without a load.
Something is drawing too much current in the bad supply.
 

Thread Starter

snaggletooth

Joined Oct 22, 2020
5
So the coffee machine works from an external 12VDC supply.
Disconnect the original supply from the machine and test it on its own, firstly without a load.
Something is drawing too much current in the bad supply.
okay that is good to know. i tried powering it on, without a load. it cost me another resistor and a little heart attack, wasn't expecting it to blow up. :)
 

Dodgydave

Joined Jun 22, 2012
9,666
That's a switchmode psu, sounds like the mosfet Q1 on the large heatsink is blown, check for shorts between the Drain and Source pins.

As a personal note from previous experience these are not worthy of repair.!
 

Thread Starter

snaggletooth

Joined Oct 22, 2020
5
That's a switchmode psu, sounds like the mosfet Q1 on the large heatsink is blown, check for shorts between the Drain and Source pins.

As a personal note from previous experience these are not worthy of repair.!
Wow you're on point. It is indeed blown. I'm kind of a newbie in electronics and will try to replace it just out of curiosity. But I think I am going to replace the whole thing with a new one if I can spot the current values i should get out of it. Thanks!
 
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