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Author Topic: 12v Charger PCB blowing fuses  (Read 7375 times)

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stevepo

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12v Charger PCB blowing fuses
« on: October 23, 2012, 17:43:46 PM »
Hi all, I have alot of these, and they all randomly die!

they are 12v (cigarette lighter) plug in and charge a small battery.

here is a picture, and also note the red circle areas, i think its possibly the top right smelt of burning, or more likely the area where there are two small components together, that definatly smelt of burning.

the fuse also blows in the cigarette charging cable end (the bit that plugs into the car) *  the fuse blows almost immediatly, the light comes on for maybe one second, then blows, and you can smell the burning from the pcb

this has happened quite a few times now, so i wonder if maybe someone has some idea of what may be wrong?



thanks in advance for any help :)
« Last Edit: October 23, 2012, 17:50:28 PM by stevepo »

kam

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Re: 12v Charger PCB blowing fuses
« Reply #1 on: October 24, 2012, 09:32:06 AM »
from what i see i can tell that this is the inductor of a buck regulator. You wanna check if the feedback of the regulator works well (some sort of resistor, small in size usually in the range of ohms or miliohms) or a feedback from the batteries. Measure the voltage across the battery and the feedback.

Generally, avoid chinese products for chargers or PSUs - funny things may happen.

stevepo

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Re: 12v Charger PCB blowing fuses
« Reply #2 on: October 24, 2012, 11:03:38 AM »
okay, thanks, yes unfortunatly these chargers come with the printers, its from the orig manufacturer. its a shame because they only give 3 month warrenty, but they are the only people who make charger for these devices, and they break between 3-6 month timeframe quite often, and at over £100 a shot, they are not cheap

kam

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Re: 12v Charger PCB blowing fuses
« Reply #3 on: October 24, 2012, 11:38:49 AM »
the only reason for the coil to fry is overcurrent - so check if something happens there were the batter connects, some short circuit or similar.

cheerio

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Re: 12v Charger PCB blowing fuses
« Reply #4 on: October 24, 2012, 19:59:06 PM »
This device is not very complex. you should make schematic of it and then you get a datasheet of the IC. There is probably a reference design that will look very familiar in the datasheet ;).
Then you check if any component is under dimensioned.  Replace those parts with better parts. This would be my first try to get these devices stable and running for a long time.

stevepo

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Re: 12v Charger PCB blowing fuses
« Reply #5 on: October 29, 2012, 18:35:58 PM »
little bit beyond me 2bh.. :(!

http://datasheets.maximintegrated.com/en/ds/MAX1758.pdf


does anyone have any idea what components are likely to fail? any clues? :D

cheerio

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Re: 12v Charger PCB blowing fuses
« Reply #6 on: October 29, 2012, 19:40:49 PM »
is there a short circuit on the output?

stevepo

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Re: 12v Charger PCB blowing fuses
« Reply #7 on: October 30, 2012, 12:12:52 PM »
Its shorting somewhere, im not sure where. :(

I heard coils can be suspect, i hope not though because if it is, its by Coilcraft, and i cant find anywhere unless i want to order a roll of 1000!

kam

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Re: 12v Charger PCB blowing fuses
« Reply #8 on: October 30, 2012, 15:13:42 PM »
I heard coils can be suspect, i hope not though because if it is, its by Coilcraft, and i cant find anywhere unless i want to order a roll of 1000!
I had found coilcraft once on ebay

stevepo

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Re: 12v Charger PCB blowing fuses
« Reply #9 on: October 30, 2012, 15:35:35 PM »
dont really know a deal about these, do you know how exact they have to be? if replaced? ;P!!

stevepo

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cheerio

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Re: 12v Charger PCB blowing fuses
« Reply #11 on: October 30, 2012, 21:04:52 PM »
Do not get those 222F Coils as you need 22uH coils and not the 2.2uH Coils.
The coil is probably not the problem. If it is shorted then the circuit will not blow a fuse imho.
Check the Diode right below the Coil first. (S1 or whatever it is labeled)
If it is shorted you know what to do. Please take the components off the board for measuring.
If this is not the dead Diode then check all other Diodes.
Post your results.

stevepo

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Re: 12v Charger PCB blowing fuses
« Reply #12 on: November 01, 2012, 18:25:24 PM »
thanks for your help, i will check them this evening, out of interest, where would i be able to locate these components, the 4 diodes near the coil are:

2x   915B340B  (i cant tell if its a 8 or a B) (this is the one you mentioned, right near the coil,

2x   909B140B

where could i locate these components if they have failed??

sorry for my questions! - ill take them out and test them this evening when i get home.
thanks all.

stevepo

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Re: 12v Charger PCB blowing fuses
« Reply #13 on: November 02, 2012, 00:04:47 AM »
those 4x diodes seem fine. :(

i was hoping it might be easy haha.

also i just realised there is more on the underside than i noticed.

in particular, whats the yellow circular thing?

thanks :)

cheerio

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Re: 12v Charger PCB blowing fuses
« Reply #14 on: November 02, 2012, 01:10:26 AM »
That is the fuse. I think it is a self healing fuse that goes high impedance when it "blows" and lowers the impedance over time to the normal level.
At least it looks like that kind.
check the Transistor Q2 if it is shorted, check the other Diodes: D13,14,16
You should also give us a closeup of this white big thing on the left. It looks quite suspicious.

To get replacement parts i usually look up the datasheet and check it against parts that are good available. Then i get the one that will do the job best in my opinion.
If you cannot find any common parts that have similar specs you have to try to find the same part somewhere in the internet. That can be pretty annoying an expensive.