Motorcycle Flasher Circuit validation

[Joe_echo]

I have an unforeseen issue. My 555 timer is now not pulsing now the pcbs have been made. Instead I'm getting a solid 12v on the output.

[floobydust]

I told you it wouldn't work and you're not listening, never mind how many different forums you've put this on.

[Joe_echo]

The circuit was breadboarded and worked as expected with the values posted. Calculations for the 555 cap and resistor combos give a frequency of around 1.5hz However on bench testing the pcb I get a solid 12v from the 555 output, instead of the pulsed signal expected. Nothing to do with your comments on transients etc.

[Zero999]

The circuit was breadboarded and worked as expected with the values posted. Calculations for the 555 cap and resistor combos give a frequency of around 1.5hz However on bench testing the pcb I get a solid 12v from the 555 output, instead of the pulsed signal expected. Nothing to do with your comments on transients etc.

Then it's:

• A mistake you made when designing the PCB.
• A PCB manufacturing fault.
• An error made when populating and soldering the components.

[floobydust]

The circuit was breadboarded and worked as expected with the values posted. Calculations for the 555 cap and resistor combos give a frequency of around 1.5hz However on bench testing the pcb I get a solid 12v from the 555 output, instead of the pulsed signal expected. Nothing to do with your comments on transients etc.

Logic then dictates your PCB has an error somewhere. Post pics so we can help.

[Joe_echo]

Completely possible.

[floobydust]

C3 is backwards, the notched end is (+).
Pin 3 goes through two resistors to Q1? You don't need R1, the cap charge/discharge is done by R2.
R3? can't be too big because you need lots of base drive for Q1 or it will roast.
The TVS will die because it's somehow protecting the entire motorcycle.
A few observations.

[Joe_echo]

C3 is indeed backwards, the footprint in altium is wrong, this awkward to be the issue causing it to not oscillate.

Pin 3 goes through 1 (750ohm) resistor to Q1 base. R3 is a pull up resistor that may not be required. R1 I couldn't comment on.

The TVS is protecting just this board and attached components, which are led lights and a few accessories. The board is fed from the battery and is grounded back to the battery. I'm not sure where you have got the whole bike is protected by this one TVS from. There is also a fuse coming from that battery to this board and the rest of the bike is protected by the factory fuse box.

The bike in question is a honda crf450x enduro bike, it doesn't come with lights as standard.