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Three fives 555 issues

edited February 2015 in General
Please help, I just finished assembly of the 555 timer kit.  I had a problem getting solder to stick on three of the legs.  I don't understand since the other hundred went fine.  But does anyone have the test parameters to test the unit.  I am looking for voltages, ohms or whatever should be arriving at certain pins.  Thank You in advance. 


  • On the pins that haven't soldered well, is there solder stuck to those pins already, or is there just bare flux? If there is solder there on one of the pins, try heating the pin for a few seconds, to see if the existing solder melts. You can check (for example) with the tip of a hobby knife or wire, to see if the solder is molten. If there is no solder wet to the pins, but just flux, you might consider scraping at the flux on the pins with a hobby knife to expose some metal. Make sure to hold your soldering iron against both the plated hole on the circuit board and against the pin of the component. Make sure the plated rings on the circuit board around the component pins are still in place. Excessive heating or pressure can damage the board and cause these to delaminate.

    Once you finish soldering, I'd advise first testing with a standard test circuit, such as the LED blinker. If you can't get that to work, double-check your soldering. If things still aren't working, please read the documentation for the kit, which is extensive, and available here:

    Using that documentation, you should be able to trace through the entire circuit to figure out exactly what is and is not working, assuming that you have a voltage source and a multimeter.
  • I need help,  it's been about a week and I still can't get my 555 to work,  I am unable to get the simple LED blinker to work.  Does anyone know of any means to troubleshoot the board.  I am looking for values at certain points on the board that I can test with my multimeeter. I did  have some trouble with a few leads not letting the solder adhere. So I have no way of knowing if I am doing something wrong in setting up the LED blinker, or did I do something wrong building the kit.  Thank you in advance
  • Kid3471,
    Once again, please read the documentation. You can test the board at every single intersection between the components, to determine exactly where the error or errors are occurring.

    If you are not sure that the solder adhered, then you should probably test that first, before trying to hook it up. 
  • Windell, thanks for the reply.  can you please tell me if I should be looking at the Schematic Diagram to get the answers that I am looking for as far as trouble shooting my problems.  when you say read the documentation can you be a little more specific. There is a lot of information to support your kit.  But as a novice all this information is a bit over whelming right now. Thank You in advance.
  • You might not believe me but I did fix something, not sure what but I did manage to get a led to light.  My only problem is I can't get the LED to flash.. does anyone have a suggestion on how to trouble shoot this issue.  Thank You in advance. 
  • The Principles of Operation guide (available on the kit's documentation page: ), walks through how the 555 works in detail, and says what every component does. Without this detailed guide, you'll likely find the schematic alone nearly useless for debugging.  

    Figure 1, the block diagram, shows the major parts of the 555 and how they are connected. Look further in for what constitutes each of those parts, and where their outputs are. Can you see a change in the output of the threshold comparator when you change the voltage on the threshold pin? Can you see a change in the output of the value of the trigger comparator when you change the voltage on the trigger pin? By asking these sorts of questions, you can narrow down exactly what parts of the circuit are working, and which are not. If you can't get the LED to flash, then it sounds like the final output (at pin 3) is not working-- but is it just the output circuit that is damaged (or not connected), or something before it?
  • Windell, is there any other means of support for the 555 timer?  other then this forum.  If so please let me know.
  • These forums and email are the support methods we offer. We do try our best to respond personally and quickly to posts or messages. I'll be following up to your most recent email messages shortly.
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