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I am trying to understand the NE555 IC in astable mode, I prototyped a circuit using "Circuit Wizard" student edition as shown in this video http://www.youtube.com/watch?v=SX01x1z7fTY at 05:36 (screenshot below) but strangely my version doesn't go in astable mode but only flashes once.

It seems like pin 7 never discharges the condensator (I tried varying the resistance but it has no effect, what is strange is that my circuit is identical to the one on the video).

Below the youtube version and mine, one flashes the other not. Do I have to set some weird setting in Circuit Wizard or is it some bug in my version?

astable ne555 non working astable ne555

EDIT: the dots in red, blue, green and purple is where I have put the probes and the logical levels are superimposed below the circuit.

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  • \$\begingroup\$ Is there a way to check the voltages on all nodes? \$\endgroup\$
    – jippie
    Jan 24 '14 at 18:42
  • \$\begingroup\$ I have added the levels of the nodes which I think might be of interest, the blue one which stays at 9 volts for me is the culpript. But in the video the same circuit works! \$\endgroup\$
    – dendini
    Jan 24 '14 at 18:53
  • \$\begingroup\$ What happens if you change the 1k resistor to 10k ? \$\endgroup\$
    – W5VO
    Jan 24 '14 at 19:03
  • \$\begingroup\$ Pin 7 (discharge) should pull to ground, but in your traces it only manages to pull to maybe 8V. Try to find out why tat happens. Eg. put a series 100E resistor in series with pin 7, then check the voltages on both sides. Does it manage to pull to ground in that case? \$\endgroup\$
    – jippie
    Jan 24 '14 at 19:10
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    \$\begingroup\$ It looks like you have a dead short across R2 -- the connection "dots" at either end are a giveaway. Remove the extraneous wire, and it should start working. \$\endgroup\$
    – Dave Tweed
    Jan 24 '14 at 19:23
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It looks like you have a dead short across R2 — the connection "dots" at either end are a giveaway. Remove the extraneous wire, and it should start working.

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