MPPT Solar charge controller

[Cortana]

Hello all!

I have a charge controller that stopped working recently. The unit is not under warranty anymore. It has served me well for a good while now. I though maybe someone here can help figure out what is the problem with it, or it will probably end up in the bin. Which would be really unfortunate.

Symptoms are:

-Meter showing inaccurate reading in regard to the actual battery voltage. The meter shows 16 volts when connected to batteries instead of the real voltage 12.4.
-Thus not charging because circuit is detecting over voltage. (The threshold for over voltage for this unit is 100v. My PV array produce around 72v max). The lights blinks even when Pvs are disconnected.
-Green LED is flashing, alternating between PV and BATT.

The failure is not due to a short made from a wrong connection, because it failed during operation.
I've checked for any signs of burned components, everything looks normal at first glance.

My guest would be bad Mosfets because their pressure pin were slightly deformed.

My knowledge of electronics is limited, but can take advice and execute them.

Here, take a look and let me know what you think.

 

[(*steve*)]

A reasonable working assumption is that the fault is in the voltage measurement part of the circuit (it may not be, but it offers a way to direct our initial investigation.

What you would probably be looking for is a thin track coming off the +ve to the battery which leads to maybe a couple of passive components then to a pin of the mirocontroller. It may be more complex than that, but it's a place to start.

If you can't find that, look where thin traces from the battery +ve go. Are there any ICs it goes to? WHat is the IC. Maybe we can figure out what it does and if it is part of the voltage measurement.

 

[Cortana]

I'm on it,

Will post photos and progression tomorrow,

 

[Cortana]

The microcontroller of this board is the STM32F103 in the top right.
There are several variants on their site. I'm not finding something that looks like ''cat6''.
http://www.st.com/en/microcontrollers/stm32f103.html?querycriteria=productId=LN1565

On the other side of the board VE+ connect directly to the mosfets.

 

[Cortana]

I can unsolder the toroid filter and the capacitors if you want. They are quite in the way to see the pcb traces.

Fortunately I have good eyes for reading codes of the chips. Some are just unreadable tough. They sprayed the board with a thin coat of varnish. Some components are laser engraved on their surfaces, saving the deal, others only have paint. The varnish bonds to paint and goes away when I scrap the varnish off.