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schematic for mercury 2500w 12v power inverter

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byronboy

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Hi, guys.
I am repairing a fairly new mercury 2500w 12v power inverter for a friend of mine which initially when connected to a 12v car battery and switched on gave no 230v ac output.The green power led was lit and no fuses blown.I checked all the mosfets and found no fault.It is quite a sophisticated design
using 16 irf1404 fets and 2 banks of 4 transformers in some parallel arrangement eventually driving into 8 18n50 fets.It also has 2 ka7500 and 1 LM325n ics.I discovered 4 in4148 diodes s/c hidden under one the transformers.I replaced them now the inverter works with a 60w bulb as a load.I measured the AC output.With no load connected the output was correct at 230v,but when the bulb is connected the output seems to rise to about 260v.I don,t wish to connect a heavier load at this stage.It is of far eastern design like most are so any current schematic would be helpful.
Many thanks, Byronboy, from Cornwall, UK.
 

It seems the output level is not controlled anymore. Check for the feedback curcuit to the controller as shown in the picture.
Some Z diodes died or the rectifying diodes are gone.
Thomas
 

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It seems the output level is not controlled anymore. Check for the feedback curcuit to the controller as shown in the picture.
Some Z diodes died or the rectifying diodes are gone.
Thomas

Hi, Thomas. Thanks for the info.I discovered my digital meter was faulty on the AC range which was
giving me incorrect voltage readings.I bought a cheap analogue meter which showed the inverter was working fine,so it turns out it was the 4 1N4148 diodes all short circuit under one of the switching transformers.They are tricky to remove because of restricted access so it was easier to fit new ones on the print side.To try and remove the transformer would require a very heavy duty iron,even my weller gun and a solder station iron together could not melt all the solder.
But all is well,thanks again.Peter.
 

Ok Peter,
You desoldered and pushed back the broken diodes at top side to disconnect it and used the other side to insert new one ?
Congratulation! So your item is working again and holds the AC output level at any load, right ? Did you check it?
Thomas
 
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