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 Bridge Rectifier test



Bridge rectifiers are actually 4 diodes sometimes in a pastic package or sometimes actually 4 actual diodes (see pic)
Their purpose is to convert the mains AC to DC which is then smoothed my the mains smoothing capacitor (47uf to 400uf at 385v to 400v) in UK the mains peak voltage is usually about 310v to 320v on my meter


Find the bridge rectifier :-
Look for the mains input lead, follow it from the power on/off switch to the PCB (printed circuit board)
On the pcb look for 4 diodes or a block of plastic with 4 legs (usually with + ~ ~ - marked on it, see picture below).
If its 4 separate diodes and your meter has a diode test function (beep),

I have No diode test meter
test each diode (power off and unplugged) by connecting a prod to each end of the diode and then reverse the prods
One way should give a short beep and read about 0.35 to 0.7 and the other way it should read 1.5 or more.
test all diodes in the area (the bridge 4 are normally identical).

If its a block type then connect meter red lead to one of the ~ legs and the black lead to the + leg its should read 0.6, move the red lead to the other ~ leg and the reading should be the same.
Now do the same test with the test prods reversed and the reading should be high.
Now connect the red prod to the leg marked -
and the black prod to one of the ~ legs again 0.6 to both the ~ legs and when you reverse the prods the reading should be high.

300v ok now


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