I'm building a circuit from a schematic - K6BEZ Antenna analyser enter image description here

Note there is no connection to pin 8 or 4 (Vss and Vdd) on the uppermost op-amp - as there is in the bottom one.

The circuit is not working - there is never any voltage at A0 - leading me to think there is something wrong with the top "half" of the circuit.

I have not used op amps before. It strikes me as odd there is no ground connection and no voltage supply to the op amp in this half of the circuit.

Is it likely just an omission in the schematic (i.e. should I connect up pin 4 and 8 as in the bottom op-amp), or is this a valid application for an op-amp, and I have some other issue?

Cheers in advance.


As JRE says, the MCP6002 is a dual op-amp - you only need one MCP6002 to build this circuit. Both op-amps in the package get their power and ground from the same pins.

If you are using two MCP6002 packages, then both packages need power and ground connections (but then you're wasting two op-amps.)

  • \$\begingroup\$ Ah- THAT'S why the two op amps are both labelled U2. It's the same chip. I did wonder why half a dual op amp chip had been used twice over. I figured it was a typo. I'll patch in power and ground and report back. \$\endgroup\$ – tomfanning Jun 25 '17 at 5:40

The MCP6002 (link to datasheet) contains two opamps.

They share the powersupply pins. The second opamp doesn't need to have a power connection shown because the power pins are shown on the first opamp.

If the circuit doesn't work, the problem lies elsewhere.

Check that you have placed U2 properly - if you got it rotated by 180 degrees it won't work.

Follow all of the notes in the assembly guide. I see that at least some versions had incorrect silk screening that could lead you to place parts incorrectly.

  • \$\begingroup\$ Thanks- I've not clocked that there is only one dual op amp chip in the design- repeated on the schematic. Easiest fix for me is to patch in power and ground to the second chip- and learn from the mistake to reduce costs for the next iteration :) \$\endgroup\$ – tomfanning Jun 25 '17 at 5:43

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