LCR Meter for In-Circuit Testing

[mapleLC]

I was wondering what the characteristic/feature of this meter is called that allows for in-circuit testing as you see here in this video:

https://youtu.be/mxz3-fGs1Lk?t=1160

My impression was that you had to pull caps to test them, so I would like to be able to repeat this with a bench meter.

[Kleinstein]

A in circuit test is not 100% reliable, and it depends on the circuit. The relatively large electrolytics at the supplies are usually OK to test unless there are several in parallel. A common and relatively reliable in circuit test is to check the ESR of large electrolytics - when showing to high an ESR the capacitor is usually bad. However there is a chance to have a parallel capacitor that is not obvious and may result on low ESR even if the capacitor one thinks to check is bad. In theory an inductor can cause a resonance and this way get a wrong result, but this is rare.

There is always a chance to have a parallel path and thus read a higher capacitance than the part one is measuring at. So to low a capacitance reading is usually a sign of a bad part.

Ideally an in circuit test would run with different frequencies and check for a consistant result. This way one could detect things like a resonance.

As a common failure mode, that is reasonable measurable in circuit is high ESR, it would make sense to have a meter that also shows ESR.

For in circuit tests it helps if the test runs with a relatively small voltage, like < 400 mV peak. This way diodes and similar junctions are usually off and there is little chance to damage the circuit. A test with higher voltage is more likely to get effected from other circuit parts.

The low test voltage would be the main point on how well a meter is suitable for in circuit measurements.
Having a somewhat higher test frequency (e.g. >= 10 kHz) also helps as this reduces the effect of parallel resistive paths.

[coromonadalix]

+1


Some tests who are done with an meter may not be good at all,  an good lcr meter will have an serial and or an parallel mode  to test ''in circuit'' capacitor or inductances,  sure it can measure an resistor too

it can help pinpoint a few things BUT  for better results, you alway have to remove the part from the board, many things can affect the ''read'' values



EX: working in smps psu's, they are design to work with frequencies, not in pure DC / linear mode,   sometimes you tests a few things and they appear as shorts,  but when under a normal functionning mode  they are okay ....

Same for other electronic equipment,  it can vary a lot

[Grandchuck]

[ve7vie]

MrCarlson likes his Circuit-test for that: https://www.eevblog.com/forum/testgear/lcr-meter-for-in-circuit-testing/

Circuit-test still has a similar model......https://www.circuittest.com/dlm-260-digital-lcr-meter.html