Where's the Bug?

[seanchan00]

Hi Guys,

I carefully followed advice from all of your inputs and replaced the FET. Still the same so I rang up an engineer for help. It seems I had interpreted the schematics wrong at the FET area. I connected both the Gate and Drain to the negative thick wire. After correcting it I saw the amber lED come on together with the load then the amber LED flicker out but the load is still conducting. Adjusting the 1 K pot did not make a difference. Have I burned the FET again? Measurement with the ohm meter show conduction between drain and source even with circuit off the battery.

SeanChan (:<)

Why open a fresh story on this?

Please continue it in the original story because spreading it out all over the board makes it impossible to track what you are doing.

COmments disabled to encourage you to follow through on the original.

Editor

[Flux]

Yes I think you have killed the fet again by connecting it wrongly. If the led is switching on and off it is likely that the rest of the circuit is working.

I am not quite sure what you did with the fet, but they don't like wrong connections.

If you sit the fet on the bench with its plastic side up and the leads towards you, gate is on the left, source is on the right and the drain is in the middle.

Drain goes to your dump load, source goes to the circuit ground and the gate goes to the 100 ohm resistor to pin 3 of 555 and also to your led.

If you are using something other than the IRFZ40 then it must be a N channel fet.

Flux