Hello,
I connected an ordinary 12V switching power supply at home to my cheap and fully functional almost new 2600W 12V car/solar inverter for a minute or two, because I didn't have a battery to power it and I just wanted to test if the cooling fan was spinning (I replaced just the fan it was too noisy, I only took off the top lid to do it and never touched the circuit).
It beeped and complained about the power supply and it showed the "power failure" LED, with the LCD display and the USB port functioning as usual and the voltage being right on. I thought nothing by it, since I didn't connect a load or anything and the 12V from the switching PSU probably weren't clean enough for it to accept it.
Now the huge problem is that when I connected it back to the solar battery in my garden shed, it would still beep and show failure. The device had been perfectly working for weeks, mostly with minimal load.
I disassembled it and I checked all the MOSFETs with a multimeter, I watched inverter repair videos, the large fuses are fine too, the solder work looks all solid and right, I tried the old fan as well in case the device measured if it was spinning ... none of the ordinary things seem to make sense. Obviously this is not a normal kind of failure for an inverter, since it seems to have been somehow caused by powering it without a battery.
I suppose there is some kind of very small security fuse blown somewhere that's for the ICs (can't find anything), or something of the sorts, but I just don't know what to look for and where.
Do you have an idea where the problem is? Could you maybe point me in the right direction?
It has mostly SMD components. My understanding of electronics is rather basic.