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Mercury 600VA UPS not working

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New Member

My Mercury 600VA UPS does not start inverting when mains fails. When the mains comes back it supplies normally.

What can be the problem? does anybody have the circuit diagram?



Most Helpful Member
Good chance the battery is bad. Have you tried running it with a different battery that is known to be good?

Does you battrey thats in it have the right output voltage while its under load? or just sitting unhooked?
Last edited:


New Member
thanks for the response.

yup. i've tried with a new fully charged 12V (approx. 13.8V) batt.


New Member
In general its quite rare to find schematics for inverters, since they're proprietary designs by the manufacturer. so try what Tariq said, else go out & buy a new one, they're cheap nowadays!


New Member
try changing the switch of the invertor (if your ups has one separately for the invertor).. if it doesnt work check the relay ,,,one that is used for switching..if it doesnt help ... then either your transformer is burned-up or circuit is damaged
thanks but it gives an output voltage when connected to main suply.
this means everythings ok.
also there's a cliking sound when input changes i.e the main suppy goes and comes. relay works

swithc is ok. no separate one for inverter.

so i'm looking for the circuit diagram in case a component is bad.

can anyone help pls?


New Member
but when mains supply fails, the invertor goes switches off. (invertor is bad may be?)

so how to repair buddies?


New Member
If your invertor is square wave generator than it should be simple to check the transistors one by one.. cause square wave generator's circuit diagram is simpler than sine wave's... even if you have sine-wave generator you will have to do the same thing..check for any sign of smell of burned component or look for any burns on transistor
(which are attached to the heatsink) ..mostly there is transistor's fault, or Transformer's.
if it is transformer then u should better buy new invertor, it would be much more convenient
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