Circuit Board testing for dummies...me?

[dan]

I'm currently learning about electronics from a book i bought and the internet. So to try out what I've been reading i bought a kit to assemble. It's a digital clock with a 24 hour relay timer. So I've soldered the thing together and hooked up the power supply and...nothing. A green led on the board lit up but the display did not so now i want to figure out what went wrong. How do i test it? test to see that each part is making contact and working properly. I don't see any shorts on the board. I have a little circuit testing meter but don't really know how to use it. Hope you guys have some suggestions for me, Thank you.

[HardwareHacker]

It's hard to offer specific advice since each electronic circuit has it's own unique structure.

Here's how I would approach this:

Check the instructions that came with the kit to see if there is advice on where to measure voltages on the circuit board. These are often called "test points". Usually this involves placing the black lead of the multimeter on the "ground" portion of the circuit card (you may need an alligator clip to do this) and then touching the red lead of the tester on the test point. The instructions will hopefully tell you what voltage you should read at those points (use the voltage setting on your meter that is appropriate for what you are trying to measure).

If you find a that the test points do not read what they are supposed to, or you have no instructions at all then you need to carefully go through your project and look for common problems:

- bad solder joints. Sometimes it might look connected but it isn't; if any joints look "sloppy" try to carefully reheat them.

- solder "bridges" - these are globs of solder that connect two parts of a circuit together: this creates a short-circuit.

- wrong connections . easy to do.. make sure the wires and components are in thier right places

- wrong orientation - some components can go in several different ways but will only work in the right orientation. Some good examples include transistors, IC's, some capacitors (esp electrolytic types), diodes etc.

- heat damage. Sometimes the soldering process can heat up components too much and burn them out. This might be hard to see; often you need to see if a test point is good on one side but bad on another side of a component to verify. Replacement parts are required if this is the problem. IC's are especially prone to this.

- faulty parts. The parts themselves can sometimes be tested outside of the circuit ie: resistors, diodes, transistors. IC's are difficult to test.

Try contacting the kit supplier if you are stumped and see if they have suggestions.

Good luck!