Hi all. The magnet board in LAH is giving me nightmares. I'm hoping someone can give me another perspective on troubleshooting this as I'm not sure where to go from here.
I have read over a lot of magnet board threads on Pinside and have read Clay's guide, and everyone suggests rebuilding the magnet board as a first step, so I did. I installed three new IRL540N MOSFETs, as well as a new 74LS273 chip. I added the suggested capacitor across the clock and ground circuits on the chip. I also installed three new fuses under the playfield.
The problem is that, whenever the magnets are activated (i.e. multiball), two of the FETs fail, causing the magnets to lock on, and blow their associated fuse under the playfield. I replaced the FETs, double checked my other work, installed new fuses, but the same thing happened again. The same two FETs keep shorting. Strangely, the third magnet works just fine. All of the magnets have the same resistance and there is nothing wrong with them visually.
I'm not really sure where to go from here. I have rebuilt the magnet board a few times, but something is causing the FETs to short and I'm not really sure what there is to look at further up the chain. Any ideas are appreciated!