Circuit Board

ey_up

Hi guys

I didnt know whether to post this is technology or here but here goes. Its christmas time and my low voltage lights blew. I am probably wasting my time but would anyone be willing to identify each of the components on the below circuit board. Ultimately I would like to work out which bit component has failed and try to replace (more out of hobby / interest that any real need - i will probably buy new anyway). I have tried searching the numbers with mixed success.

The circuit controls flashing lights with in/out power "A" & "C" and 1, 2, 3, 4 being to the lights. The speed is controlled by component marked 104. The circuit failed by my error upon reconnecting after I had cut the cables to put them through the wall. The power was still connected (remember low voltage) and something blew. If I bridge the circuit with my fingers the lights all work so I suspect one component failed.

Any pointers appreciated. Thank you

stator

Looks like you've got one variable potentiometer on the bottom left. One capacitor to the right of that (lower). 4 diodes at the top. In center is one resistor. Q2 - Q4 are transistors.

Not sure what this is sticking out of the board on the left side.

Blown capacitor is a common fault

http://www.electronicsandyou.com/electronic-components-parts/electronic_component_name_abbreviations.html

zax47

The bit we can't see is a small daughter board with encapsulated IC on, probably a timer circuit (555 type) that's doing the mark/space for the flashing, controlled by the potentiometer. I see empty spaces for at least 1 fuse (top, 2Amp?) and something (4K7 resistor? 4.7uF cap?) between the diodes (which are arranged as a common bridge-rectifier, turning AC to DC). Resistor & cap down the middle are trying to keep the power to the IC clean and limited, amongst other things.

As there's little reverse-current protection (well, none) on the outputs I'd guess you've fried one or more of the output transistors and probably whatever is encapsulated on that daughter board.

Rubidium

It won't be the capacitor or other power supply components. Capacitors dry up or leak electrolyte due to age, not fail suddenly when live wires are cut.

The 'missing fuse' mentioned above is actually a thin track on the PCB. The other missing components are due to this PCB being used for different applications.

You say that "If I bridge the circuit with my fingers the lights all work so I suspect one component failed"

Where are you bridging the circuit board as that will give a good indication to what has failed.

I suspect that your fingers are providing enough leakage current into the base of transistors Q3 - Q4 causing them to turn on, driving the lights (LED's?)

Therefore the most likely component that has failed is the 8 pin sequencer chip. If this has failed you would likely find it hard to source a replacement.

ey_up

Thank you for the replies. Its interesting to learn what each bit does as last time I did anything remotely like this was at school. I am going to use your pointers and see if I can learn a bit more and identify the problem after borrowing a multimeter to see if I can understand which bits are working when I bridge the connections with a finger.

Not expecting much luck but we will see....

Le_Kirk

You won't fault find a faulty IC (chip) with a multi-meter as you need to know what the IC is designed to do upon receipt of signals (voltage) from other parts of the circuit.

Mankysteve

The board that is sticking out looks like a die on board with the black blob of epoxy. Most likely it will be the bit that has blown, it will be custom micro processor jobby and there will be no way of getting a replacement. Someone with the time could swap it out for something else but it would take a bit of work.

My advice would be to take it too ypu local tip recycling point.