12VDC to 230VAC Inverter Repair

[HR71]

Hello,
I am new here. I need some help. I am trying to repair a 12VDC to 230VAC inverter and trying to learn at the same time too. This inverter was working fine for sometime and the initial problem was that it suddenly started to generate 57VAC instead of full 230VAC. It opened up the circuit and found out that it has the following MOSFETs. (Two CS150NO3, Four IRF1404 and Four 2SK3522). I measured the Gate/Source voltage of the four 2SK3522 and found out that two of them had only 1.9V and two others had 20.6V. as per dtatsheet 1.9V is below the GS(th) value for this MOSFET. So I decided to check the waveform of the Gate/Source supply. Unfortunately while doing this I found that the 12V supply Negative wire insulation was melting and disconnected the supply. Then I found out that the one of the IRF1404 MOSFET was shorted and that the Gate/Source supply voltage of that mosfet was 12V (same as battery supply)(marked with a red circle in the image) while other 3 mosfets G/S voltages were 4.57Vdc. Now my immediate task is to solve this high voltage at this mosfet. Also, G/S voltage at the CS150NO3 mosfet also at 11.7Vdc (I am not sure that this is normal or not).

1). I really appreciate if anyone could help me to identify the components as per this circuit that you think that may be between the 12V supply and the first IRF1404 mosfet and some insights as per your experience to get to the solution.

2). And finally, I need support in sorting out the 2SK3522 final output of the inverter as well. Hope anyone can shed some light here.. Thanks!

 

[kellys_eye]

Make? Model? Schematic?

For most small inverters it's often not worth the cost/effort to try to repair as replacements are so cheap these days. MOSFET failure is common and simply replacing them all can often fix the situation unless there are other issues with the circuitry but unless you have access to an oscilloscope then finding the 'other' fault will be difficult.

 

[HR71]

Hello Kellys_eye,
Thanks for the reply. Unfortunately this is an inverter from china. so no model or schematic available. I have an oscilloscope but i have to fix the first problem first in order to use the scope on the second problem.
rgds,

 

[Bluejets]

Time for a new one.................

 

[HR71]

Well I found the issue to the issue No:1. a rookie mistake!! while resoldering the IRF1404 mosfets after removing for checking, a minute solder blob has shorted Gate and Drain of the 1st MOSFET. it was so tiny... but.... . Thanks for the encouragement guys. Now please support me with the Issue No 2 also. I will update once i get the graphs. cheers!

 

[Delta Prime]

Well I found the issue to the issue No:1. a rookie mistake!

Not bad for rookie!
But I think you'll find issue number two is the same.
You got a link where you bought your device from China?

 

[kellys_eye]

2). And finally, I need support in sorting out the 2SK3522 final output of the inverter as well. Hope anyone can shed some light here.. Thanks!

Apart from replacement you need to identify the main control device (IC) as the design of these inverters often follows the (very) basic operating principles as shown in that devices datasheet which are readily available and a good source for info on what to test/check.