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LC100A LC Meter Fix

Turn a cheap LC meter into a highly accurate device!

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The LC100A is a fairly popular and cheap LC meter available on aliexpress and similiar sites. It is advertised as an up to 1% accurate device (depends on range) with a resolution of up to 0.01pF and 0.001uH. Unfortunatly he device I received had errors up to 50% and was thus not usable at all.

Thanks to a comment on aliexpress I found out that the issue was low quality components for the LC resonance circuit, likely the manufacture substituted them because they were cheaper. I think the main issue was that the max frequency was well above the rating of the inductor, so it's effective inductance dropped and threw off the measurements.

I replaced the parts with the best I could find (part names below) and the performance is within spec now. During my research I found a manual and a low-res schematic; I've up-scaled the latter manually and have both files attached below. The pictures are watermarked to prevent the seller from using my pictures.

Portable Network Graphics (PNG) - 848.15 kB - 12/21/2020 at 13:24

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msword - 181.00 kB - 12/21/2020 at 13:24

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Portable Network Graphics (PNG) - 963.97 kB - 12/21/2020 at 13:24

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Adobe Portable Document Format - 156.24 kB - 12/21/2020 at 13:32

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Adobe Portable Document Format - 477.61 kB - 12/21/2020 at 13:32

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  • 1 × MURATA 22R104C inductor, 100uF 10%, self resonance 7MHz, high Q>90
  • 1 × WIMA MKP4F031003C00JF00 capacitor - PP film, 100nF 5%
  • 1 × WIMA FKP2J011001D00HI00 capacitor - PP film 1nF 2.5%

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