Electronics > Beginners
7812 voltage output too high?
Zuul:
Hello
This is a power supply for a Philips NMS8220 I am trying to get sorted. The computer seemed to be working fine but of course I just had to open it up and poke around in there. Measuring +12v at the motherboard connector and it was way high.
I swapped out all the caps, the 7812 and 7912 regulators, but I am measuring over 17 volts out of the 7812 on the pin.. the voltage in is around 19.5v
I have swapped out the 7812 again and it's still about the same. It is a 7812CT and the original one is in the trash so I couldn't tell you the numbers on that...
The fuse that is missing in the pic was at some point in time been "fixed" with aluminium foil by the previous owner :(
What should I try to get this fixed? Please treat me as a total noobie because, you know, I am! :-+
Excuse the fuzzy pics.
mikerj:
Measure between the centre pin and output pin of the 7812. There may be something that lifts the center pin voltage above ground, either accidentally or deliberately.
wraper:
There might be resistor in parallel to it. Probably R8. In that case increased voltage without load present is normal.
Zuul:
Thanks for replying
OK, it measures steady 17.03v on the pins
Zuul:
Right, is it safe to plug it in? Where should I measure next? At the connector?
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