Specifically, I have a RadioShack KV300 inverter (300W) that has an output of 115V AC at 60Hz. How is this frequency set, and can it be adjusted to 400Hz? I suspect the values of C23 and C25 affect frequency. Please see attachment. The ICs on the board are as follows: KA3525A, KA324, SG3525AN, and HA17358. Unfortunately, I do not have the circuit's schematic.

I greatly appreciate your time! Thank you.

 

Without the original schematic, you may have to run the normal output through a circuit specially designed to boost frequency -

What is your goal...?

 

Like Packrat said, without the schematic your pretty much working blind. But both the KA3525 and the SG3525 (both the same but different manufacturers) are PWM chips. So that's where I would start to look for changing frequency, pull up the data sheets for them to see how to change frequency. You will have to figure out which chip changes the output frequency though.

 

The ka3525a is altered by the resistor on pin 6,,or the cap on pin 5, alter the resistor between 2k and 200k as per datasheet.

It can be adjusted from 60Hz to 430Khz, but you will affect the tuned circuit of the transformer.

 

Changing to 400Hz may be out of the range of the components currently on the board.

Usually, they adjustment is for 50Hz or 60Hz operation. When the board was designed, all parts were optimized for 60Hz. Increasing that by nearly 7 times would interfere with the existing capacitors, inductors, and transformers. It might work, but it wouldn't give the rated output.