SSLC084V42 Switch Mode Power-supply / Li-ion Battery Charger

[Mad Professor]

Hi All.

I am looking for some help and advice with regarding to fault finding and repairing a SSLC084V42 Switch Mode Power-supply / Li-ion Battery Charger.

This is the 2nd unit that has failed, the 1st failed unit was just scraped, this unit is just over a year old and has also now failed in the same way.

Sans Electronic Co.,Ltd
Model: SSLC084V42
Input: AC100V-240V AC 1.8A MAX 47-63Hz
Output: 42.0V DC 2.0A

I have done very little work with SMPS, I have always mainly used linear power supplies.

The fault / problem is that there is no output from the unit.

So far I have checked the fuse and the bridge rectifier on the mains side.
There is rectified mains voltage all the way though the circuit up to the switching FET but nothing out of the FET.
Near to the switching FET is a small SMD IC, I am guessing that this is the driver for the switching FET, but once again I can't seem to see any output from this to the FET.





The MOSFET is a SMK1060

IC1: OB2202CP

Can anyone here please advice where I should start looking to try and find the fault with this unit.

Thanks for your time.

Best Regards.

[tautech]

Near to the switching FET is a small SMD IC, I am guessing that this is the driver for the switching FET, but once again I can't seem to see any output from this to the FET.

Most likely so. This you need to identify it and get the datasheet.

You can then check if it has power to its supply pin, normally there will be a resistor from HV (rectified mains) and some bulk capacitance ~20-50uF.
I've seen faulty caps and/or open resistors prevent these IC's from starting up.

Operation of the IC can be confirmed with a scope on the gate of the MOSFET while the IC is powered ONLY with DC from a PSU.

[Rasz]

a small SMD IC

read the markings
on the pic it looks like R1 and R2 make a divider powering this chip? check voltage

[Mad Professor]

Thank you for your replies.

I have been able to read the markings on the IC

IC1: OB2202CP

Testing the Pin8 (BO), and Pin6 (VCC) came back with zero volts. with the unit disconnected from the mains I did a continuity test, and found a dead short from GND and VCC. Looking over the PCB some more I found a solder bridge across C2 (10uf 50v) this is across the power rails for the IC, after removing the solder bridge I now have some voltage readings at the IC.

Pin4 (GND) and Pin6 (VCC) = 1.91vdc
Pin4 (GND) and Pin8 (BO) = 1.40vdc
Pin4 (GND) and the output between RX1 and RX2 = 24.5vdc

Looking at the datasheet the min VCC voltage for this IC is 11vdc

I have been trying to draw a Schematic but I can't get my copy of DaveCAD working and I keep on making errors 

Looking at the PCB and tracing back from Pin6 (VCC) it seems to be getting power from the output between RX1 and RX2, via R5 a 100k resistor. one side of the resistor is reading 24.5vdc the other side is reading 1.91vdc

[tautech]

Looking at the datasheet the min VCC voltage for this IC is 11vdc

UVLO = 14V min. You must have this voltage for it to start.
To check the IC is working power it with a PSU and scope pin 5 Gate.
Check current draw also, datasheet says ~5mA, if it's drawing lots more than that I'd be concerned.

[Rasz]

Looking over the PCB some more I found a solder bridge across C2 (10uf 50v) this is across the power rails for the IC, after removing the solder bridge I now have some voltage readings at the IC.

that is a little disconcerting. How could that happen? some lose solder rattling lose inside? shorting and immediately melting? this is weird, where did it come from? something else must be burned
your pic is too weak for inspection, cant see any burn marks/components

[qu1j0t3]

I have the same unit, with same fault. Green LED lights, but 0V on output.

I did replace the two 470µF capacitors and that didn't change a thing.

So I wonder if it is the same root cause as OP's. I'm prepared to dig further. I have good DVM, scope, but not a lot of experience debugging SMPS.

[keymaster]

Be aware that  most of the chargers for lithium won't output voltage ,if they don't see a battery plugged in .

[qu1j0t3]

Ah, I was wondering about that. So I could set up a dummy load of sorts. Any suggestions of current?