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Car battery charger

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Aleks

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Few days ago, I got 2 battery chargers to see if I can fix them. I'm currently working on one of them. They are both of the same type, Switch-Mode supplies. The power FETs (IRC840) are OK and so are the coils. As far as I can see, the FETs aren't getting activated and I can not measure any voltage after them. Their gates are connected via two ICs - "A T530 0721" which I believe to be opt-couplers to the output of a UC3525AN PWM IC.

Behind the PWM IC there are a whole bunch other components, like opamps (LM258), transistors, caps, resistors, and a relay at the output of the device.

I think that something is interfering with the pulse generation. Maybe its the PWM IC that is the cause or maybe something else, I really don't know and I don't know how can I test the PWM IC.

Can anyone give me any tips on how to debug the device even further and get to the source of the problem ?

Thanks in advance,
Aleks
 
If this is an offline (AC powered) switcher, they often take out a lot of circuitry when they blow. It's pretty much hopeless to troubleshoot without a schematic.
 
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If this is an offline (AC powered) switcher, they often take out a lot of circuitry when they blow. It's pretty much hopeless to troubleshoot without a schematic.

Yes it is AC powered charger. I don't think that I will be getting the schematic any time soon. Maybe I can try and see if the PWM chip is working somehow, any idea how ?
 
Yes it is AC powered charger. I don't think that I will be getting the schematic any time soon. Maybe I can try and see if the PWM chip is working somehow, any idea how ?


The 3525 chip can be powered by your bench psu....Set to something like 12v applied to pins 13(+ve) and pin 12...Do this with the main power off!!

Scope the waveform on the outputs, pins 11 and 14.....

Having a copy of the data sheet will help you too in checking the voltages at other pins
 
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