Where are these Diodes on my board ?(monitor power supply board)

Thread Starter

UnnamedUser159

Joined May 3, 2016
501
Last edited:

AlbertHall

Joined Jun 4, 2014
9,826
Where exactly are the meter leads connected?
The diodes have an AC voltage coming in and a DC voltage coming out. Your meter is set to a DC voltage range and if it is connected so that the meter sees an AC component in the voltage then you might well get that sort of response from the meter.
 

Thread Starter

UnnamedUser159

Joined May 3, 2016
501
yes. i have measured now these :
the common cathode(the middle pin) of the both secondary diodes and the max value shown on the DMM is on one 0.6 on the other one 0.8 on range 20V
So the both are dead ?
 
Last edited:

Thread Starter

UnnamedUser159

Joined May 3, 2016
501
so. i have new one analogue meter since today.

The both diodes :
x1 ohm check - low ohms reading, oposite probes - no reading
x10k full scale(let`s say) and with oposite probes absolutely no reading

My Esr meter does show:
IMG_20180320_153533.jpg

So where should be the truth and why?!
 

DickCappels

Joined Aug 21, 2008
6,381
Does your meter have a diode test mode? Use that if you have it.

Otherwise, you can use the AC voltage range to measure the inputs (the anodes) of the rectifiers to see whether there is a large signal on the diode. If there is, and there is very little DC output that points to a diode problem.

If the AC side of the diode shows a very small signal then you should look upstream for the problem since you have shown that your diodes are not shorted.
 

Thread Starter

UnnamedUser159

Joined May 3, 2016
501
obviously i have shorted STK0765 which is power mosfet - i hear beep when check drain to source with curcuit check mode.

I will look for one new and then put it on board and the other desoldered elements too and will see what will be.
 

AlbertHall

Joined Jun 4, 2014
9,826
Otherwise, you can use the AC voltage range to measure the inputs (the anodes) of the rectifiers to see whether there is a large signal on the diode. If there is, and there is very little DC output that points to a diode problem.
I think this is a switch mode supply so the AC may be too high frequency for good readings on a standard multimeter.
The diode test range is a much better bet.
 
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