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I am trying to repair mainboards with VI component tester. (Such as this device and that device.)

I check the characteristic VI curves of the components on the card and identify the defective parts which is diode, condenser, mosfet, IGBT...

In general, these devices do the measurement correctly, but especially in circuits such as diode and condenser parallel.

enter image description here

The VI curve of the capacitor is shown on the display when measured at the end of the diode.

enter image description here

Is it posible to measure the diode VI curves, even though a capacitor is in parallel to it?

Is there a way to look at the parts without disassembling them?

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  • \$\begingroup\$ A diode in parallel with a capacitor will produce a unique pattern. Take a diode and capacitor outside of the circuit and try the parallel combination with your tester. If you are going to be successful with this troubleshooting technique, you will need to remember various patterns, you won't always have isolated components. The pattern in-circuit will look somewhat similar, but other parts may affect it. And of course, if one if bad, you won't necessarily be able to tell which one, but you may have narrowed it down. \$\endgroup\$
    – Mattman944
    Commented May 26, 2019 at 12:31

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So how should the tester know you're testing the diode but not the capacitor?

Remember what inductivity and capacity do: they introduce a lag between current and voltage (or vice versa).

So, no, if you have a capacitor in parallel to your device under test, you can't get a correct V/I curve for that device if you excite it with an alternating current.

What you can do is do a really slow increase in current, wait until the steady, DC case has settled in, and then move on to the next higher current.

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If you know how read schematics, understand what impedance a node should be , recognize XY trace characteristics, know how to damage parts, and understand the importance of source impedance that must be high for testing CMOS and low for big DC caps then the Huntron Tracker is an excellent tool.

This schematic tells me a 48V transformer with 120VA is converted to DC with a 4700uF cap. That means it must supply 3Adc a the cap must be able to absorb current with f*C and have a low ESR in the 30m Ohm or less range.

So here the source needs to be low Z. 1 Ohm at the most enter image description here

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  • \$\begingroup\$ Thanks for reply but your image link not showing (I think its about our country has problem with imgur) can send a new link \$\endgroup\$
    – mehmet
    Commented May 27, 2019 at 9:49

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