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I'm trying to build an LED chaser circuit using a 555 timer and a 4017 counter. I've built the circuit successfully on a breadboard, but now that I tried to create a soldered version it just does not work.

On my breadboard version I can observe the clock signal coming out of pin 3 just by measuring the voltage there and I see a proper oscillation. On my soldered circuit there is 0V respective to ground, and no oscillation.

I compared the voltage on all pins of the 555 in my working and my non-working circuit, and the difference I found is that I see no voltage on pins 2,6 and 7 to ground.

How can I identify the problem now? Could I have damaged the resistor, the potentiometer or the capacitors by causing too much heat during soldering (I use sockets for the ICs, so they can't be affected by the soldering)? If that is a possible problem how would I check if a component is damaged?

I checked the soldering joints and resoldered any that looked suspicious. Should I resolder every connection, or is there a way to locate the potential bad soldering joints?

This is the schematic of my circuit, pin 3 goes to the 4017 timer which I omitted from the diagram.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ The voltage on pins 2 and 6 are loosely connected to that on pin 7. Since that should be pulled up to 9V by a hefty 1k resistor, that's where I'd look first. Measure resistance from pin 7 to ground : possibly a short; or to 9V : possibly open circuit. Check the voltage at both ends of the 1K resistor too. \$\endgroup\$ – Brian Drummond Aug 20 '13 at 16:06
  • \$\begingroup\$ Related circuit question: electronics.stackexchange.com/q/79348/2028 \$\endgroup\$ – JYelton Aug 20 '13 at 16:20
  • \$\begingroup\$ @JYelton Probably the same assignment... ;) \$\endgroup\$ – SLaG Aug 20 '13 at 21:32
  • \$\begingroup\$ I built a lot of 555+4017's before I started using AVR microcontrollers. :) I thought it might be useful to link the questions to each other. \$\endgroup\$ – JYelton Aug 20 '13 at 21:44
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How can I debug ... I see no voltage on pins 2,6 and 7 to ground.

If I understand correctly, those are all fed via R1 so I'd look closely for a dry joint at R1. Even if C1 was shorted, I'd expect twiddling R2 would produce something measurable at pin 7.

If you disconnect power and pull the 555 out of the socket, I think you should probably be able to test c1,c2,r1,r2 in-circuit with a multimeter.

For example I'd expect resistance between socket positions 4 and 7 should be 1K

etc.

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    \$\begingroup\$ Thanks! That was the problem, after resoldering the 1k resistor it works correctly now. \$\endgroup\$ – Mad Scientist Aug 20 '13 at 16:54

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