Testing the +5 Volt Supply
Set your voltmeter to measure DC voltages up to 20 volts, and connect the black (Common or Ground) lead to the negative lead of the 1000µf capacitor. Connect the red lead to the upper end of the 0.3″ red jumper wire. Turn on your voltmeter, then turn on power to your transformer and power supply circuit.
You should measure a steady +5 volts (+4.75 to +5.25) here, at the power supply output, and the red pilot LED should turn on. If you get these results, move your red voltmeter lead to the positive lead of the 1000µf reservoir capacitor. You should see about +17 volts here, possibly higher.
If you get the correct results, turn off your power supply and voltmeter, and skip down to the Discussion below. If your results are different, quickly note the results you did obtain; then turn power off and look through the following troubleshooting chart.
Output voltage is steady at +5, but LED remains off.
LED is reversed. Remove it and re-insert it in the opposite direction. Then try the power supply again.
Resistor is the wrong value or connected incorrectly. Make sure it is a 1K resistor (brown-black-red) and is connected fron the lower end of the red jumper to the left (anode) end of the LED. Then try the power supply again.
Output voltage rises to +5 volts, but then declines steadily.
One or both electrolytic capacitors is reversed. The reversed one will be warm or hot to the touch. If you leave power on too long, it will explode and leave a large mess to be cleaned up. Check and correct capacitor orientation, and then try the power supply again.
Output voltage is negative.
Your main rectifier diodes are installed backwards. Refer back to the assembly diagram and install them correctly.
Output voltage is incorrect.
7805 voltage regulator is installed incorrectly or is defective. Verify correct installation and replace if necessary.
Once you are sure that your power supply is working correctly in all respects, turn off power to your circuit and your voltmeter. Then move down to the concluding discussion below.