I have SMPS circuit which is used for charging lead acid batteries, they are 6 batteries, so charging voltage should be around 80 v , for 12v battery
What I have now that nothing at output at all
There is mosfet taking signals from uc3845B , for switching to high frequency transformer
The mosfet is ok , I’ve measured with multimeter, and it’s ok
There is no component shorted at th circuit shown
All resistors are ok
The doide at output stage is ok
The input voltage is about 230v, to the smps , I think it should be higher as the smoothing capacitor is rated at 450v

The uc3845 , i changed with another new and the same problem exist, nothing change
How can I diagnose this circuit and what else to check?

Scope the signal at mosfet gate?
Part from the circuit is shown below , the uc4845B part

 

Any replies?

 

It might help if we could see sharply-focussed pics of both sides of the whole circuit board.
Make/model of charger?
Schematic available?
What is missing from the area above R219?

 

Okay , I will photo and send
It’s a UPS by the way, 3k, Infosec E3 performance 3000 RT
The missing parts are opti-coupler I’ve taken out tested and put back , they are ok by the way also

 

Hi
are you sure the controller is UC4845B ? Did you found the datasheet?

 

Hi
are you sure the controller is UC4845B ? Did you found the datasheet?

It’s uc3845B , yes have datasheet

 

Hello
Ive found the problem
It’s the smoothing capacitor at the input of this charger, it’s completely bad, inebriate terminal not connected at all, like it’s not there and not charge at all
And so the voltage at input not the 300v, and so not enough voltage to start up the circuit