I'm wondering if anyone can help ID the component in the red box as well as the IC right next to it. I suspect that they are a diode (the tapered end might indicate polarity?) and some kind of Opamp respectively. This board is pretty old. It came out of an aircraft radio for a Cessna 150.

I tried googling "National Semiconductor JR56AB" and other variants for the IC but absolutely nothing came out of it.

I haven't physically seen the board yet. My friend just sent me the photo. Otherwise I would be doing some DMM tests on it.


enter image description here

  • \$\begingroup\$ The "JR56AB" looks like a lot code to me. I wonder if it's a 100k series part... \$\endgroup\$ Feb 15, 2014 at 5:40
  • \$\begingroup\$ Everything I'm finding points back to the LM431. \$\endgroup\$
    – Matt Young
    Feb 15, 2014 at 5:47
  • \$\begingroup\$ @IgnacioVazquez-Abrams I think you're right about the code. My searches for "100055" is bringing up aviation results so we may be on the right track... \$\endgroup\$ Feb 15, 2014 at 5:50
  • \$\begingroup\$ I have never seen a 100k series part in a DIP package. The first LCCs (ceramic) I saw (in 1982) were 100k. 10k, sure, they were available in DIP (though not plastic that I ever saw). Plus the PCB doesn't look like a high speed digital layout, so I suspect you have to keep looking... \$\endgroup\$
    – user16324
    Feb 15, 2014 at 11:19

2 Answers 2


That's a tantalum capacitor. It's a fairly common package. Check the markings in person, but the Kemet would be my first guess as the manufacturer.

  • \$\begingroup\$ You're right. I just checked Digikey and that package is popular \$\endgroup\$ Feb 15, 2014 at 5:55
  • \$\begingroup\$ @superkittens Still need to figure out what this IC is, how old is this board? \$\endgroup\$
    – Matt Young
    Feb 15, 2014 at 5:56
  • \$\begingroup\$ I believe the board was made around the late 70s to the 80s. \$\endgroup\$ Feb 15, 2014 at 6:02
  • \$\begingroup\$ @superkittens At that age, I would bet money we are dealing with an obsolete part. TI has been very good about keeping National's documentation up to date and available. I'm not finding any reference to the lot number or part in any of the documentation. \$\endgroup\$
    – Matt Young
    Feb 15, 2014 at 6:05
  • \$\begingroup\$ Yeah it's probably an obsolete part. I guess I could try contacting TI directly or if I could, decap that sucker! If only I had the means... \$\endgroup\$ Feb 15, 2014 at 6:12

it's a jfet op-amp, here's the datasheet https://www.ti.com/lit/ds/symlink/lf411.pdf

enter image description here

  • 2
    \$\begingroup\$ What makes you think it's that part? Assuming you mean the part with the JR56AB marking, the jfet in your datasheet has the marking "LF411CP", so we would need some good evidence that despite the different marking (and manufacturer), it's the same part. \$\endgroup\$
    – nanash1
    Jun 14, 2023 at 8:05
  • 1
    \$\begingroup\$ As nanash1 said, the device markings don't match: i.stack.imgur.com/Lc3X2.png \$\endgroup\$
    – Velvet
    Jun 14, 2023 at 10:09
  • \$\begingroup\$ My parts have the JR56AB mark on the top line and LF411 on the bottom line \$\endgroup\$
    – Rx7man
    Jun 17, 2023 at 0:06

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