Can't figure out why my 555 IC isn't working anymore

I have a 555 IC set up in astable mode with R1=100KΩ, R2=1MΩ, and C1=1uF on a breadboard powered by a 9V battery.

This gives me roughly 1.4Hz which is fine. I've actually reused this particular breadboard/555IC setup to power rough clock cycles for a few projects, but it suddenly stopped working. I figured I had accidentally pulled a wire or something, but I've rebuilt it 10 times now, replaced the wires, replaced the IC, replaced the capacitor, measured the resistors, and I just can't get it to work properly again.

When I connect power to the circuit the output on pin 3 turns on the resistor/LED combo that I have on pin 3 briefly, but then stays off instead of cycling. When I disconnect and reconnect the power, same symptoms. With the power attached I measure a 9V drop between the two leads of R1. Does that make any sense? R2 has almost no drop.

I'm at a loss. How else can I troubleshoot/measure this to figure out why it's not working?

I can post a photo/schematic if it would help, but it can't get more basic. I'm not using a capacitor on pin 5 but I don't think that matters. Certainly didn't before.

Post the circuit

Here's the schematic

krjhitch said:

Here's the schematic

Click to expand...

Pin 5 CV should not be grounded, either a cap to 0V or left floating.

It shouldn't matter if you are using a standard or low-power 555 IC. It has many varieties - LM555, UA555, MC1455, etc..
This circuit should also work with a 556 and a switch-selectable timebase.

ericgibbs said:

Pin 5 CV should not be grounded, either a cap to 0V or left floating.

Click to expand...

This was exactly the problem. I'm not sure what happened, I think I must have accidently put a ground symbol on it while doing the schematic, and then remembered that 'you don't need to use pin 5' so I remembered not having a capacitor, but then I forgot that it was supposed to be unconnected.

Much appreciated.