Duracell CEF23 gone bad after first use

[khankll]

i bought this charger but it behaved strangley.. first i had charged 4 cells in my maha mhc801d .. 2 AA and 2AAA were fully charged there.. and left for 3 days un used.. then i bought this chager Duracell CEF23 ... pluged in the batteries first i tried the 2 AAA and the leds were blinking red.. which i think means error . or some say it will blink red if u insert fully charged cells.. i removed these 2 AAA cells .. then i tried 2 AA and the corresponding leds were solid red.. then i inserted another 2 AA and its leds were also solid red.. after a while one cell indicators changes from red to green... now there are 3 cells with solid red indicator and one cell with solid green led .. after 5 or 10 minutes i noticed all the leds are off.. no blue led (power on led ?) no cells correspoindng leds are on... removed the charger and tried re inserting it.. but still no luck.. no led will come on...
it is not working with 12volts dc input ..
i got no weired smell at 1 foot distance.. no clicking sound... no spark or tickling sound.. i was sitting near it..
i opened it all caps are ok .. no buldge etc.. nothings seems burnt.. no broken things..
i just checked its USB charging mode from 4 cells it worked ok.. i inserted 4 AA Energizer 2000mAH cells and pressed the button at the bottom then the led for usb charging came blue and my cell phone was charging..

but i cant charge the cells form mains.. no light when inserted into mains..and neither can it charge cells..
here are pictures of item.. from another forum.. mine is same .. there is no difference .. no burnt spots or anything ..

http://i133.photobucket.com/albums/q74/robin24k/Misc/DSC00071.jpg

http://i133.photobucket.com/albums/q74/robin24k/Misc/DSC00075.jpg

whats the issue ?
thanks

 

[khankll]

the fuses are also ok..

 

[CocaCola]

If there isn't an obvious part(s) you can identify as failed, like smoke, cracks, bulges or burn marks, you are likely looking at it being cost effective to just purchase a new one...

 

[khankll]

ya i just purchased new one but i just want to try my free time on it...
because it makes me immensely happy to repair items....

 

[Harald Kapp]

There seems to be no obvious sign of a defect in your pictures. You will have to work your way through the circuit. Since the charger works from the DC input, it is obviously the mains section that has a defect.
- check the input side of the transformer. Mains voltage present? If not check traces (and fuse) from transformer to mains input.
- If the primary of the transformer sees mains voltage, check the secondary. Is low voltage (AC) present? If not -> transformer defect.
- If low voltage AC is present, check low voltage DC after the rectifier (across the smoothing capacitor). If no voltage present -> recifier or capacitor are defect.
- If voltage is present across the smoothing capacitor, check the signal path into the circuit. Where does the DC get lost? The fault is almost certainly near that place. A possible cause could be the voltage regulator.

 

[khankll]

There seems to be no obvious sign of a defect in your pictures. You will have to work your way through the circuit. Since the charger works from the DC input, it is obviously the mains section that has a defect.
- check the input side of the transformer. Mains voltage present? If not check traces (and fuse) from transformer to mains input.
- If the primary of the transformer sees mains voltage, check the secondary. Is low voltage (AC) present? If not -> transformer defect.
- If low voltage AC is present, check low voltage DC after the rectifier (across the smoothing capacitor). If no voltage present -> recifier or capacitor are defect.
- If voltage is present across the smoothing capacitor, check the signal path into the circuit. Where does the DC get lost? The fault is almost certainly near that place. A possible cause could be the voltage regulator.

the charger doesnt wors from dc input .. i,e it does have a provision to charge the 4 cells from either a 12 volts dc input or 120-240volts Ac input.. but its not charging from one now..

the charger also have the provision to charge a usb device either from the 120-240volts ac or 12 v dc or 4 cells .. of which currently on the 4 cell option is working..

so i guess the problem is after the chopper transformer or after the the ac-dc conversion process..... a block of cirucuit after that is i think faulty..




there are two regulator ics one is 7805 one is tl431...

also it has a chopper transformer not the regular linear transformer .. can someone tell me some good resource on these ? how to identify its input and output sides ? its smps not linear...

also the pics are not mine but mine are ditto same .. visual nothing wrong with them.. no broken trace after x-raying using powerfull led to watch through the other side.. components are secured properly... there are two fuses both are ok.. i checked few diods they were conducting either way by using the diode check of multimeter.. i think some parallell circuit is there thats y i can get reading either way..

so can anyone refer me a good source on these chopper tansformer ? there seems to be many pins of that transformer ...

 

[khankll]

a bit update.. i have replaced tl431 and 78l05 but broblem is not solved..

there are a lot of diodes .. and two diodes conduct either way. when i set my mm to diode test it shows reading both ways.. others only show one way ? what that means ?
well diodes conduct one way but is it possible that conducting other way is due to some other circuit in parrallel to these diodes which provides alternate path ?

 

[(*steve*)]

a bit update.. i have replaced tl431 and 78l05 but broblem is not solved..

there are a lot of diodes .. and two diodes conduct either way. when i set my mm to diode test it shows reading both ways.. others only show one way ? what that means ?
well diodes conduct one way but is it possible that conducting other way is due to some other circuit in parrallel to these diodes which provides alternate path ?

Your assumptions are correct. If those diodes are suspicious, I would unsolder one end and check them again.

 

[khankll]

thanks will try and update ..

 

[khankll]

all diode are ok.. those that i suspected wre sr260 and they are ok and read 145 on my mm using diode test.. there was a transistor tl431 that was also replaced ..didnt worked.. also replaced a 7805 but no luck...

caps all look ok .. no leak or buldge .. board traces are ok..

i suspect the transformer like little thing .. how to check it ? inductors and fuses are also ok..

 

[(*steve*)]

We could really do with some pictures of the board. Sharp enough to read component markings clearly. Both sides of the board would be nice too. At least one image from directly above.

 

[khankll]

picS are given in first post ..

 

[(*steve*)]

So they are...

 

[(*steve*)]

OK, so the USB port has power. This means that the power supply is not entirely dead.

Do any of the ICs have markings on them? Your use of a flash makes it very hard to tell from this image.

If they do, google for the datasheet and see if they have power on the power pins.

 

[CocaCola]

Do any of the ICs have markings on them? Your use of a flash makes it very hard to tell from this image.

We really could use a sticky with examples of good and bad photography techniques... Simple things like taking the pictures outside on a sunny day vs using a flash indoors make a world of difference...

 

[khankll]

after thorough inspection i found one smd transistor (?) swollen.. i compared the board with another good charger board and found that the swollen transistor was labelled "WF7K' it was smd transistor ..

so is there any alternative?

 

[(*steve*)]

I've never seen a swollen transistor. Perhaps a nice sharp picture that's NOT taken with a flash?

 

[khankll]

I've never seen a swollen transistor. Perhaps a nice sharp picture that's NOT taken with a flash?

its melted and is disfigured not as sharp rectangular shape.. its like a charchole blob .. its hardly the sahpe of good one...

the affected area is shown in red

 

[khankll]

the faulty transistor ? is labelled as WF7K in the ok board . can someone give me any more info on it ? i cant find it on google. is there any alternative to it.. its smd..

 

[(*steve*)]

I can't find WF7K in my list of device markings. Sorry.