Battery charger problem

[2PAC Mafia]

Hi guys,

a customer sent me a battery charger manufactured at Italy, I see somebody already replaced a capacitor (C7) and the fuse but not working yet. I see it has a SMD 6 pin component marked as 73B32 or 73832, not sure about that, it´s used for SMPS transformer.

I attach the schematic I made from that part. I find two problems:

First one is about the power to that IC1, as you can see at schematic it should be powered first through a 1M resistor, then a transistor which bypass the power to the IC. OK, this is really strange. If I measure at resistor R8 I have 320V at one side and 0,7V at the other side. I have checked R8, ZD1, Q1, R12, C6, C8 and D1. All the components are good. I found frozen solderings at transistor but that was not solving the problem. In fact, if I power C8 with my power supply power goes into pin 5 from IC1!!! It´s really strange, I measure continuity between upper point from resistor and bottom point to be sure there was contact... I don´t know why I get only 0,7V there.

My second problem is about IC1, when I power it there is not PWM output to switch the transistor, it´s DC output at pin 6, so I think it´s damaged and I´ve been looking for some info about it and I can only find 73832 info, but it´s not in that SMD package so I´m not sure...

 

[alec_t]

How did you check C8? My guess is it could be leaky. Try a replacement. Alternatively, could pin 5 of the IC be a (near) short to ground?

 

[2PAC Mafia]

How did you check C8? My guess is it could be leaky. Try a replacement. Alternatively, could pin 5 of the IC be a (near) short to ground?

Thanks for your answer Alec. I tested with LCR meter with D factor plus ESR meter. It is OK. Just in case I replaced by another one and the same.

Finally, I open the line to pin 5 and then I have 17V going into IC1, this means the IC is sending voltage near ground. Pin 5 to ground is 380 ohm. The IC is damaged.

Now, the question is to find the IC... 73832 shows only 8 pin packages...

 

[2PAC Mafia]

It shows MCP73832 which is 5 pin and different function. Also FAN73832 in 8 pin package.

 

[2PAC Mafia]

I have found this:

https://es.aliexpress.com/premium/7...ative_id=SB_20151007230804&isViewCP=y&catId=0

From China, I tried to get some info about the product asking them on a chat, but no way with chinese people... Seems to be the product but also is saying something about LED I guess.

 

[2PAC Mafia]

I see it has secondary for 12V and 36V, 12 then changed to 5V for microcontroller and 12V for relay, amplifier, 36V directly for output, the charger is 36V 1A output and is used for different gardening machines. If I tell you inductance values and Mosfet type, is it possible to use another PWM IC controller? Or can I give a pulse frequency with my signal generator just to see when I get 36V and 12V? Which value should I start testing?

I know I can adapt another SMPS but I´m looking for a cheapest option for my customer.

 

[2PAC Mafia]

Done, finally changed IC 73B32 (no information, no datasheet in Internet) and working right.