Hello Amirahp,
Please refer to your modified picture below:
View attachment 142615
The two red arrows are indicating your Vcc points. You need to place
your multi-meter on either one and observe if there are any changes
to the voltage. That means clipping the Vcc and ground points with parrot
clips or something else you you can monitor the voltage during the start
up sequence and perhaps 5 minutes after the UPS has stabilized.
The two green arrows means that you need to trace back to the circitry
involved with where CN7A connects to. You need to pay close attention
to any zener diode/s that may be within that feedback circuitry.
You may need to lift one side of the diode/s to measure any reverse
leakage. If its an SMD type, you'll have to remove it from circuit to get
an accurate measurement.
If you haven't checked any resistors in this section, then check them.
You'll find that quite a few of them will be 1% types. You'll need to take
the close tolerances into the equation and ensure none have gone beyond
the 1% difference.
I hope the above helps.
Please keep us updated on how you get on.
Regards,
Relayer