What flyback transformer it is?

Thread Starter

LAOADAM

Joined Nov 21, 2018
541
Hi,
I am checking a charger that used a 14-tap transformer, the measurement as follow:
R8-10 = 0.6 Ω;
R12-14 = 0.4 Ω;
R4-7 = 0.3 Ω;
R3-7 = 0.3 Ω;
R3-4 = 0.3 Ω;
All other pins are empty, no soldering actually except pin13 which soldered but no connect to any other pins on transformer, that did connected to other component.

A schematic picture not a real transformer attached.
Thanks
Adam
schematic diagram.PNG
 

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MrChips

Joined Oct 2, 2009
23,528
Resistance measurements do not reveal anything about the transformer except the DC resistance of the winding.
You need to apply AC voltage at the specified frequency to the primary winding and measure the AC voltage at the secondary winding.
 

KeithWalker

Joined Jul 10, 2017
1,785
I would suspect that the last 3 readings you show are the resistance of your test leads. It is probably a fairly high frequency transformer with a ferite core and very few turns.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
541
Resistance measurements do not reveal anything about the transformer except the DC resistance of the winding.
You need to apply AC voltage at the specified frequency to the primary winding and measure the AC voltage at the secondary winding.
Thanks,
I'll try it. I didn't do that way because of the first input signal is from the + output of a Rectifier bridge and through a UC3842 module generate PWM to excite the transformation (not very sure yet). and I don't know what voltage should use to do the test.
 

Ian0

Joined Aug 7, 2020
2,218
If you'd mentioned UC3842 earlier, we would have known immediately that it was a flyback transformer.
I'm assuming that the charger runs off the mains.
You'll find one terminal of the transformer connected to the drain terminal of a MOSFET. I bet that MOSFET has failed.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
541
If you'd mentioned UC3842 earlier, we would have known immediately that it was a flyback transformer.
I'm assuming that the charger runs off the mains.
You'll find one terminal of the transformer connected to the drain terminal of a MOSFET. I bet that MOSFET has failed.
Thanks.
You are right.
The charger used: ru7088r/ mbr20100ct/FS10KM/UC3842.
It looks on the bright side, there are few resistances burnt, the true reason maybe like you said.
burnt R.PNG

The terminal 10 of the transformer connected to the drain terminal of a MOSFET FS10KM, that is controlled by UC3842 module through gate.
 
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Ian0

Joined Aug 7, 2020
2,218
Looks like they got their dog to solder it.
With that many components soldered on the back, I'm not surprised it failed. Obviously it didn't work as they designed it, then they added various bits to see if they could fix it.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
541
Looks like they got their dog to solder it.
With that many components soldered on the back, I'm not surprised it failed. Obviously it didn't work as they designed it, then they added various bits to see if they could fix it.
Thanks.
Seems it is.
I draw a diagram of it, need help please:
1. any thing wrong with the drawing?
2. any improvement can make?
3. how the J6 on/off control the 12v/24v output?
 

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Thread Starter

LAOADAM

Joined Nov 21, 2018
541
Ok,
Attached the drawing again for a easy look. and still need help on how to modify it to avoid burn again.
Thanks
post5.PNG
 
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