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LC100A LC Meter Fix

Turn a cheap LC meter into a highly accurate device!

nqtronixnqtronix
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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.

3_LC100a_schematic_upscale.png

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

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4_User-manual-of-LC100A.doc

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

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5_comment_aliexpress.PNG

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

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MURATA_2200R.pdf

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

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WIMA_MKP4.pdf

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

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View all 6 files

  • 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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briker.fm2019 wrote 04/04/2022 at 21:16 • point

i have this kits but ic stm broken. can you share firmware for replace new ic stm to me?

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nqtronix wrote 05/28/2022 at 20:03 • point

Sorry, I don't have a programmer or the required software to read it, and even if I could, I'm certain it will be locked.

Sorry for the late reply, hackaday.io's notification system is broken and I didn't get an email.

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paulandreasen wrote 01/09/2022 at 00:59 • point

Mine was 4-6% off on lo caps, 20-40% off on high caps. After your mod, I get 40-300% off on lo caps, 1-4% on high caps. Duh! Used your exact parts. Replaced caps with Vishay 1%'ers and samo-samo. Any guesses?

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nqtronix wrote 05/28/2022 at 19:59 • point

Did you remember to zero before the measurement? This LC meter measures the DUT with an LC oscillator, and I replaced the critical parts with parts which are stable across a wide frequency range. If you have exactly the same parts, I have no idea that the issue could be.

Sorry for the late reply, hackaday.io's notification system is broken and I didn't get an email.

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paulandreasen wrote 05/29/2022 at 02:41 • point

Yes, I did zero it out. Weird. I cannot find any problems with the board or wiring, and replaced the parts (I had ordered a few of each - cheaper) I got a friend who works on Vandenberg Space Force Base nearby, in their PMEL shop, to check all he components. All were within a couple % of ratings. Just my luck I guess. Good thing I am getting too old to do much now!

Thanks for the reply tho!

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anthonyfu wrote 11/24/2021 at 13:01 • point

is it possible to modify to measure inductance as low as 1nH, capacitance as low as 1pF?

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nqtronix wrote 05/28/2022 at 20:02 • point

With such small values the parasitic inductance/capacitance will dominate and you'd need a much better setup overall. You'd be better of buying a suitable device in the first place.

Sorry for the late reply, hackaday.io's notification system is broken and I didn't get an email.

  Are you sure? yes | no

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