ECN Forum Forums Photo Discussion Forums Photos for General Discussion Alarm PC board (UK)

Demonstrating one of the perils of being right on the coast, this is the PC board from the outdoor sounder box of an alarm system which has been up for about 6 to 7 years.

It doesn't look too bad from the front:



But looking at the back shows how once the protective screen starts to deteriorate at the edges, the board soon starts to suffer from the weather:



The strobe light had stopped working completely, and the alarm had started to sound randomly, sometimes just a "chirp," sometimes a blast of two or three seconds.

I've taken apart a couple of Ford automotive engine control modules and the circuit board and all the components are invariably covered with some sort of coating that feels like silicone rubber. I suspect this is what is really needed to provide good corrosion protection to the board.

Interestingly, these ECMs are installed in the passenger compartment, not the engine compartment.

That silicon rubber looking stuff is called conformal coating and that is precisely what it is used for. I used to work for a company that built the electronics for VitaSpa hot tubs. We had to cover all of the boards with that messy stuff, so they would survive all of the chlorine/bromine vapors involved with the tubs.

The other use for the conformal coating is to hold components in place as a form of protection from vibration.

Funny story about ECMs in passenger compartments: Years ago the VK Holden Commodores (released in 1984-5) had the ECMs mounted in the passengers footwell behind the kick panel. These were the first model to have an ECM fitted.The prevoius model did not have an ECM fitted so this was the location that the fire extinguishers were fitted.

On the changeover from the VH to VK models, the fire extinguihsers were fitted onto the passengers side kick panel.

All was going quite well until the time came to start the cars to move them out of the shed. Can anyone guess what happened?

The replacement unit I used for this job was a better model with extra internal protection, along with proper plunger-operated tamper switches instead of the spring-to-a-cheap-PCB-mounted-switch type of the original, etc.:







I can take a guess, but I can't think why.

For years, the self drilling screw was the fasted method to fit the brackets for the fire extinguishers which worked well for years until the it was discovered where the ECM was mounted by accident...

Luckily it only happened to one car before it was discovered why it was a task to get the screws to tighten.