555 astable not going low


I have a 555-time setup in astable mode. R1: 470k R2: 470k C: 10uF

I'm measuring with my multimeter on 20V to see the Voltage rise and drop, but it idles at about 6.7V endlessly. There is a 9V battery powering the Vcc.

Any ideas what could be going wrong with my setup?


Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png or pdf?

Also a picture of how you have set it up.

What configuration, astable, monostable?

What output are you expecting, that is frequency, duty cycle?

Tom..Hope to help but need this information..... :)

Hi, using a calculator program. ASTABLE 0.1Hz at 66% duty, thats a pulse that is ON for 6.6Seconds, then OFF for 3.4Second.

Tom.... :)


This is the schematic I used to connect the 555. I'll post pictures here in a few.

Please see picture.

Please see picture.

Please see picture.

I hope these help diagnose my problem. Is it possible I broke the 555 or something?

Hi, put a 10uf capactor across the supply rails to help with bypassing, have you swaped the 555 for another? Also check that all the pins that are connected to gnd or supply are actually connected by checking at the pins of the chip. The other worriy, I cannot read any numbers on the chip body, are you sure they are LM555?

Tom...... :)

I added the 10uF capacitor to the power rails and it didn't help. I wish I had another 555 to test out. I'll have to buy some more. Would it still run even if I fried it?

The chip reads "TS555CN". I'm guessing my assumption that all 555s are all the same is probably wrong.

Hi, you have the CMOS version TS555CNof the 555, it is configured a little differently due to its construction.


Tom..... :)

Hi, just a suggestion, try using components that will produce a higher frequency,ie use a lower value C1. A combination of high value resistors and an electrolytic cap that has leakage current may be the problem. Even try smaller resistors..

Tom..... :)

I think the supply rails may be split in the middle and some jumpers need to be added.
(See dwg attached.)

(The CMOS are the same as the TTL, but there’s an astable config. possible w/ the CMOS that isn’t so with the TTL.)


I just checked the rails and they are all receiving the power from the 9V. Really confused about this. I've been tinkering with it all day and at some point it was working w/ an led I was using but I haven't been able to replicate it. I'm also unsure if with a very quick on/off cycle my multimeter is sensitive enough to register the changes in voltage. Is an oscilloscope the most sensitive means of tracking the on/off state?

Hi, use components to give you 1Hz, use a 470R resistor in series with a LED connected to pin3 and gnd. Make sure the LED is the right way round, if not then LED will not work, no damage done.

Tom..... :)

So I setup what you described and as I attached the battery for the last step, the light turned on for a second and then turned off again and remains off. Any idea. This was happening earlier too. I even tried disconnecting the battery and connecting again but the LED didn't turn on again this time. I checked the LED afterwards with a continuity test on my multimeter and it still works, so I'm not sure what is going on with this 555.

Hi, it sounds like your 2 to 6 link isn't working ,but you have that connection. Leave the battery disconnected for 15 seconds or so, then try again. If it works then the 2 to 6 is okay. Check that the reset pin is connected correctly, to pin8 or supply. The 555 is not resetting. What value cap on pin 5, try without it.

Tom.... :)

So with the 0.1uF cap from pin 5 to ground, the LED remains lit endlessly. If I remove the cap form pin 5, the LED is endlessly off. In my book it only recommends the cap on pin 5 in monostable, but I’m pretty sure my setup is correct for the astable. I’m thinking this IC is just screwed somehow…

Hi, I'd agree its time to swap it out, if you are going to buy a new one make sure it is a LM555, or NE555 or UA555. That is a plain generic 555, not a CMOS one.

Tom..... :)

Don’t be so quick to throw in the towel.
I’ve attached that alternate, CMOS-version only astable config. I mentioned.
Give it a try first.
Connect the power leads right to the rails of the section that you’re using.
Lower values of R and/or C will make the period shorter (“faster”).

I think it’d all work better with some proper wire (wiring) - as opposed to those 50cm jumper header crap things.

With a 7555, 500 k? and a 10 µF tant - I’m getting about 5 sec HI and 4 sec LO [ :grin: ].
Using two 4.7 µF electrolytics ( in || for 9.4 µF), my time is about 7 1/2 sec [ 8) ]
So, that’s the effect of capacitor (component) tolerance
The datasheet’s formula: f = 1.4 * RC f = 1 / 1.4 * RC [so t = 1.4 * RC]