This was originally posted on APC forums on 7/31/2016
Hello Apc experts.
I had an old APC Smart UPS 750VA 500W 230V usb version (SUA750) Not used for sometime and yesterday I changed its batteries with new one. I turned it on and heared the tone then the onlinr (sine wave icon) along with the left half leds which were dim flashed for about 10 seconds or less then stopped flashing and the battery led indicator kept on the rest were not. I then measured the output voltage and frequency using a Multimeter , it was 230 V and around 200Hz and highly fluctuating AC frequency. I plugged a table lamp just out of curiosity and It worked and the frq. Was the same ~200Hz. Now this is a totally wrong frequency and I guess in might damage my electrical component
I plugged a smal hair dryer and It didn't work, then I plugged a CFL lamp (which I tested and were working) with the hair dryer and the hair dryer worked slowely but the CFL lamp pruduced loud buzzing noise.
What is actually going on? How to fix this frequency issue?