Must be pilot error. I tried the AAC calculator and it gave 1.396e+4mS.

The calculations for the timer in question were so simple that I could do it without a calculator (i.e. in my head). 20 * .7 = 14

 

My bad. But it should be around ground once the timing cap gets to 10V...

Agreed, but that doesn't seem to be happening.

 

connection between pin 2 and 6 good.

OK, can you try a 10uF timing capacitor? Perhaps pinching the one from pin 5?
The leakage of the 1000uF may be too great.
If that doesn't give you flashing then please post a good picture of your circuit that will let us follow the connections.

 

The leakage of the 1000uF may be too great.

Granted the labeling in the picture wasn't that great, but I read 100uF...

 

Check the connection between pins 2 and 6.

Problem solved. Rebuilt the circuit using a new capacitor and a new 555 chip from a different package. LED flashed, however slowly, about 6 seconds. Flashing rate increased be changing capacitor. Apparently capacitor or chip were shorted. Thanks for your help.
George

 

Apparently capacitor or chip were shorted.

Couldn't have been a shorted capacitor because it was charging to 10V. Also couldn't have been a shorted timer; whatever that means in your context.

 

Is there to test a 555 to determine if working correctly. Made a circuit, worked. Tried to change flashing rate by changing R3. Burned out LED. Changed LED. Only lights, does not flash.

 

Is there to test a 555 to determine if working correctly.

You build a test circuit; just like the manufacturer would do.

If you make an astable, the only other function to test is reset. If you want to do parametric testing; that would be more involved.

 

You build a test circuit; just like the manufacturer would do.

If you make an astable, the only other function to test is reset. If you want to do parametric testing; that would be more involved.

The circuit flashed. I changed value of R3. The flashing rate changed. Went to a lower value of and burned out LED. Changed LED and made R3 bigger. LED lights but does not flash. What changed? The only thing I see is something changed in 555. Why dose't it flash?

 

The circuit flashed. I changed value of R3. The flashing rate changed. Went to a lower value of and burned out LED.

Changing R3 would not change the flashing rate.

What did you change R3 to?

To see if the timer is working, you can measure the capacitor voltage to see if it's changing and alternately charges to 2/3VCC and discharges to 1/3VCC. You can also monitor the output to see if it's changing; it should alternate from near ground to near VCC.

The output can source 200mA (assuming you're using a bipolar timer), and it should have been able to destroy an LED without being damaged.

Changed LED and made R3 bigger.

Are you certain the replacement LED is functional and connected correctly?

 

Changing R3 would not change the flashing rate.

What did you change R3 to?

To see if the timer is working, you can measure the capacitor voltage to see if it's changing and alternately charges to 2/3VCC and discharges to 1/3VCC. You can also monitor the output to see if it's changing; it should alternate from near ground to near VCC.

The output can source 200mA (assuming you're using a bipolar timer), and it should have been able to destroy an LED without being damaged.
Are you certain the replacement LED is functional and connected correctly?

Which R changes the rate?
I reduced R3 to 100 ohms. Still flashed. rate a little quicker. R3 10 ohm burned LED. Tested LED with battery and resistor. No good.
Cap measured at 94uf. Input V and V across cap same. Cap not charging but measures OK.

 

Changed LED. LED lights but does not flash.

 

Which R changes the rate?

R1 or R2. R1 would affect charge, R2 would affect both charging and discharging.

I reduced R3 to 100 ohms. Still flashed. rate a little quicker. R3 10 ohm burned LED.

What is the supply voltage?

Cap measured at 94uf. Input V and V across cap same. Cap not charging but measures OK.

What is the voltage on pin 7?

 

Supply V 21 V DC pin 7 21V

 

Absolute maximum supply voltage for the LM555 is 18V.

 

You're risking the life of 555...


Datasheet says the Max Vcc for Bipolar 555 is 18V and cmos is 16V.

The NE555 is about the same... See datasheet attached

 

Absolute maximum supply voltage for the LM555 is 18V.

Circuit worked for a day until changed R3. ??? Does that mean I blew part of the 555?

 

Possibly but it's impossible to tell from here. It has certainly been over-stressed.

 

Possibly but it's impossible to tell from here. It has certainly been over-stressed.

Checked with another meter. 16V. output of source should be 16V

 

Why would the circuit flash for a day or so and the failed when I changed the value of R3? I thought RC was the time. Does R2C change rate? Which way? Increase R2 lower rate or increase rate? I am trying to understand this circuit.