I created the PCB based on the schematic shown below. I ordered the PCB shown below that I designed and I connected up. After I soldered all my parts into it and connected a 9V battery, nothing happened. The battery just got very hot. Any ideas where I went wrong?

Parts included are:

  • 1 NE555P (555 timer IC)
  • 1 CD4026BE (IC)
  • 3 10K resistors
  • 1 100k resistor
  • 1 22uf capacitor
  • 1 1uf capacitor
  • 2 FSM2JH (push buttons)
  • 1 232 Keystone 9V Battery Snaps & Contacts
  • 1 SC39-11GWA (seven segment LED)

On PCB design U5 = 555 timer, U3= CD4026BE (IC), seven segment led is below U3

PCB design of circuit

Circuit schematic based PCB off of

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    \$\begingroup\$ Are you sure the battery was connected with correct polarity? What is the purpose of C2? Please show us photos of both sides of the PCB with all components and tracks clearly visible. \$\endgroup\$ Oct 12, 2021 at 4:12
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    \$\begingroup\$ Did this design work when you breadboarded it??? My money is with Bruce above though, you connected the battery backwards.... Check it with your voltmeter. \$\endgroup\$
    – Kyle B
    Oct 12, 2021 at 4:20
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    \$\begingroup\$ for reliable operation, you need power supply bypass capacitors - 0.1 uF or so, between the Vcc and Ground pins of the ICs (but omitting them won't cause the battery to overheat.) Why are the ICs U1 and U2 on the schematis, but U3 and U5 on the board? \$\endgroup\$ Oct 12, 2021 at 5:10
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    \$\begingroup\$ picture of the real board as-built (both sides) would help determine whether there are any construction/assembly issues, like cold solder joints or stray wires \$\endgroup\$
    – MarkU
    Oct 12, 2021 at 6:55
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    \$\begingroup\$ It seems like the shown schematics is not the schematics linked with the PCB layout because the identifiers doesn't match. Could you include the one you entered in your CAD software ? Maybe you thought you have routed your board like the provided schematics, but you made a mistake and it's not the case. I think no one will take the time to check that every single track of your layout picture corresponds to a wire on the provided schematics. This is usually done automatically by your CAD software. \$\endgroup\$
    – Blup1980
    Oct 12, 2021 at 8:17

1 Answer 1


I figured it out. I had it grounded out because on the seven segment pins 3 and 8 are connected. I did not know this and connected pin 3 to vcc and pin 8 to ground. After cutting the connection of pin 3 to vcc the pcb worked as needed!

  • 1
    \$\begingroup\$ Good work. I think you can accept your own answer after some delay. This will mark the question as solved and the system won't keep popping it up on the front page looking for an answer. \$\endgroup\$
    – Transistor
    Oct 12, 2021 at 20:56

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