I noticed an odd 'event' on an MK-168 that I recently aquired.
While testing a capacitor the tester produced a screenfull of repeating characters.
The capacitor was 2u2, and had a fairly high esr, and I wondered if this 'bug' was peculiar to the MK-168 or maybe other testers/firmwares exhibit the same flaw.
In the process of trying out some comparison tests I came across other limitations (some may already be known about, but I thought I would add them for completeness of the report.
As a reference device I used an LCR-300 from Voltcraft. The $20 testers included an MTester with V2.07 firmware, an MK-168 with V1.07K firmware, and a Fish4480 with V2.2 firmware.
Using a 2u2 capacitor with a 1k Ohm preset in series I obtained the following results:
Preset @ zero Ohms >>> LCR-300 ESR 2.1R, MTester ESR 2.4R, MK-168 ESR 2.5R, Fish4480 ESR 2.5R
Preset @ 102.26 Ohms >>> LCR-300 ESR 104.3R, MTester ESR 16R, MK-168 ESR 93R, Fish4480 ESR 95R
Preset @ 151.17 Ohms >>> LCR-300 ESR 152.8R, MTester EST 17R, MK-168 ESR 130R, Fish4480 ESR 130R
Preset @ 198.35 Ohms >>> LCR-300 ESR 200R, MTester ESR 17R, MK-168 ESR 140R*, Fish4480 ESR 140R
Even when higher values were tried the MTester never read more than 17R max ESR. The MK-168 and the Fish4480 seemed to top-out at 140R. Only the Voltcraft instrument continued to give accurate readings even when the preset was set at its maximum, but then you would expect that due to it being a 'professional' instrument.
It was at settings above approx 160R that the MK-168 started to show a screenfull of rubbish.
Now, I accept that these units are cheap hobby-class devices, and for such basic hardware I think they do a tremendous job. I also accept that if a capacitor has a highish ESR these units would highlight that fact sufficiently to cause the person concerned to replace/reject the capacitor concerned.
My two 'puzzles' are:
1) Has the MTester been limited to show a maximum ESR of 17R for any technical reason,
2) How come the MK-168 goes crazy when presented with high ESRs?
Just curious!