add-on fuse protection for locked coils. Anyone do it?

shardian

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add-on fuse protection for locked coils. Anyone do it?

A few weeks ago I had a spare rev. 2 board in my Lethal Weapon pin to test it out. I had a coil lock on, and it doesn't seem the game has any kind of protection to shut the circuit down. The transistor almost melted through the board, and I have a quarter sized burn mark on the metal back box mounting panel. My existing rev. 3 board apparently suffered the same fate at some point, and has been a major repair effort to get it back to working condition. Not to mention it apparently damaged the coil PIA - which has been an intermittent failure.

I shudder to think what would have happened if I wasn't there to turn off the game! Much worse, what happened when a coil locked on a route game back in the day!

As such, I would like to investigate add-on fuse protection for locked on coils. Has anyone ever done this? I know there is a kit for The Addams family and the locking on magnets issue.
 
As such, I would like to investigate add-on fuse protection for locked on coils. Has anyone ever done this? I know there is a kit for The Addams family and the locking on magnets issue.

There are lots of pins that came out of the factory with fuses on every coil. Atari comes to mind.

It wouldn't be hard to splice into the harness coming from the driver board to add fuses or add them under the playfield at each coil. I've added fuses to coils before and I always add them under the playfield.
 
There are lots of pins that came out of the factory with fuses on every coil. Atari comes to mind.

It wouldn't be hard to splice into the harness coming from the driver board to add fuses or add them under the playfield at each coil. I've added fuses to coils before and I always add them under the playfield.

Do you have a guide for what amperage Slo-Blow to use? I assume it would vary based on the size of each coil.
 
Hardy har har....

That's fine and all, but don't coils have spikes when first applied? Then of course fuses have amps they can take 100% of the time, amps they can handle for 30 seconds, and amps they can handle for a few seconds.

I would assume that this stuff would have to be taken into account based on what the coil does along with its resistance.
 
That's fine and all, but don't coils have spikes when first applied?

That's why you use slow blow fuses.

Then of course fuses have amps they can take 100% of the time, amps they can handle for 30 seconds, and amps they can handle for a few seconds.

Again... slow blow fuses are what you want to use. You could analyze the data sheets of various fuses to find the most ideal option but I would just use basic slow blow fuses and not worry about it. I'm sure you would find that in practice there's really not going to be much difference from one slow blow to another. You're protecting against shorts so you have a lot of margin for error.

I would assume that this stuff would have to be taken into account based on what the coil does along with its resistance.

It's just basic circuit protection. There's no reason to over think it. I would just use ohms law and double or triple the expected amperage. Actually I would probably just put in 2A slow blows and be done with it. TIP 102s are rated for 8A and most coils will never blow a 2A slow blow unless shorted. Obviously there are exceptions but like I said... there is a large margin for error here.

Also make sure you've got the right amperage solenoid fuse(s) in the game. In theory the solenoid fuse should blow before a shorted transistor will melt the driver board.
 
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