It says 100J and is much bigger than the other components.


It has a resistance of 2ohm when the circuit is without power, and 15 ohm when I attach power to the circuit. It has a 1nf capacitance. So it might be a capacitor, but why is it bigger than the other capacitors, and could it replaced by any 1nf capacitor?

  • \$\begingroup\$ Could be an inductor \$\endgroup\$ – Colin May 2 '19 at 11:04
  • \$\begingroup\$ electronics.stackexchange.com/questions/334128/… \$\endgroup\$ – dim May 2 '19 at 11:08
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    \$\begingroup\$ Possibly a transient suppressor. \$\endgroup\$ – Peter Smith May 2 '19 at 11:11
  • \$\begingroup\$ Thanks for the link 😁 \$\endgroup\$ – user220980 May 2 '19 at 11:11
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    \$\begingroup\$ and 15 ohm when I attach power to the circuit. It has a 1nf capacitance Don't measure resistance in a powered circuit, you can damage your multimeter. Always power off, then measure. The 1 nF means nothing, at this low resistance the capacitance cannot be measured properly. \$\endgroup\$ – Bimpelrekkie May 2 '19 at 11:48

100J and a short circuit would be an inductor.

100J is a 10 microhenry inductor. J means it is accurate to 5%

This site explains how to read inductor codes.

It also lists all the precision codes.

Short form:

First 2 digits is the value. The third digit is how many zeroes to put on the end. Final value is in microhenries.

So, 100 means value 10, add no zeroes to the end. So, final value 10 microhenries.

It seems to be OK. Inductors fail by becoming open circuits.

Don't replace it. Look elsewhere for whatever problem made you suspect it.

Do not replace it with a wire. It appears to be part of an RF amplifier. If you put in a piece of wire, you will kill the output transistor.

Do not replace it with a capacitor. The output amplifier won't work then.

In response to comments:

NEVER try to measure resistance with the power on.

Since you say it is only a short circuit when the power is on, it looks like it is dead after all.

You need a 10 microhenry inductor to replace it.

Be careful when playing with that board. Touching the gray wire to ground will kill the inductor - that shorts the power supply to ground through the inductor.

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  • \$\begingroup\$ This would make sense as it is short circuited. Interestingly it's only short circuited when the power is on. \$\endgroup\$ – user220980 May 2 '19 at 11:44
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    \$\begingroup\$ @user220980 -- measuring resistance with the power on is pretty much meaningless. The meter looks at the voltage drop across the component when it's powered by the meter's battery. Adding another voltage source skews the reading. \$\endgroup\$ – Pete Becker May 2 '19 at 11:47
  • \$\begingroup\$ Thank you. Very good to know! \$\endgroup\$ – user220980 May 2 '19 at 11:55
  • \$\begingroup\$ It's a cheap wireless microphone, which the OP might have been kind enough to mention. I doubt if anything would be damaged by shorting the inductor, but it would eliminate any useful RF output at the antenna. \$\endgroup\$ – Dave Tweed May 2 '19 at 12:31

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