Troubleshooting - 555 Servo Sig Trig
Kevin Koster 2014
Firstly, in case of trouble consult the manual - perhaps you just missed something.
If your reaction to that statement is "thanks, that's what lead me here!", when we can progress to further diagnosis.
First take a close look over the board to make sure there isn't anything quite noticeably amiss. eg. Incorrect jumper placement, bridged solder joints or components installed the wrong way around.
If there is no sign of life from the circuit, disconnect it and use a multimeter to check that there is good conductivity from the ground pin of the receiver connection to pin one of the 555 IC, and between the positive connection and pin 8. Failing that, check the Bridge Rectivier and Relay, ensure C7 is installed with the negative side facing the relay. If you find you've made a major bo bo, check none of the traces have burnt out, and consider components that may have been fried.
If the circuit is showing signs of life, but not the sort of life you were after, then the course of action depends on whether you're using it in Latching or Non-Latching mode...
If it won't go off and adjustment of trimpot VR1 to its minimum position (full clockwise) does not help, even with VR2 at maximum, first disconnect the circuit and check Q2, VR1, R1, R2, VR2, C1, C2, R7 and R8. Apply power with Servo and Recevier removed and connect the signal connection to the Receiver to positive, this should make pin b of J3 high - showing that Q2 is working (if not, check Q1 to isolate fault). If so, check there are no shorts to ground between J3a and J2c. Failing this, check that J4 has a jumper installed and D3 is conducting from pin 3 to J4a. If you have an Oscilloscope, a triangle waveform should be seen at J1a with the period set to 2ms/div.
If it won't turn on after turning off, check R2, VR2, R5, R8 and C2. Check J1a isn't high (indicating Q4 is on when it shouldn't be, check R11, D2 and C5).
If the output flickers momentarally on or off when the trigger presed, making it difficult to set the relevent mode, check the delay networks of Q3 and Q4. Make sure there is a jumper between J1a nd J1b. Ensure diodes and transistors are positioned the correct way around and that transistors are of the BC5xxB type (see "Component Notes" in instructions).
If it won't go off, first disconnect the circuit and check Q2, R3, R4, R7 and C1. With power applied and the receiver signal input connected to positive, J3b should be high (if not, check Q1 to isolate fault). Failing that, check that C2 isn't shorted to ground.
If it won't turn on with VR2 adjusted to minimum resistance (full clockwise), check R2, VR2, R8 and C2.