I own a LAH as well. That game is a mechanical nightmare.
FIRST THING ENSURE PROPER FUSES ARE USED
Here's what I would bet money on that you'l find.
If all some or all magnets don't work or blows fuse F9 or fuses on magnet power board:
Disconnect the aux driver board found mounted underneath the pf.
Manually engage the switch in front of the ripper coil. If F9 blows
don't automatically replace the TIP122, pre driver or coil for that
matter. Meter out the associated TIP36C @ Q1 on the PPB board and then
meter out the 2n4401 pre driver @Q7 and TIP122 @ Q13. Typically when
the coil locks on it blows F9 fuse on the PPB board so fast no damage
to the coil (or aforemetioned parts) occurs. Chances are that if the
TIP122 and pre driver check out good, it's simply the fuse and TIP36C
that needs to be replaced. I was pissed to find out I replaced the
"normal" components for nothing.
Replace fuse and test RIPPER coil again. If the fuse doesn't blow then
reconnect your magnet aux driver board. Keep playing (invoke as many M-
BALLs as you can.) If F9 EVENTUALLY blows ONLY when having the aux
driver board installed then use the capacitor fix mentioned above. If
the fuse DOES blow (immediately when RIPPER coil activated) then most
likely you'll find that the TIP122 transistor and pre driver are
damaged, replace TIP122 @ Q13 with a more robust TIP102 and replace
the pre driver (2n4401) @ Q7, Ohm out your RIPPER coil. If it falls
under spec (which this particular coils spec is 3.8) cut one leg of
the diode off and re-check it. If it meters out at ~3.8 replace the
diode on the coil. If it still meters under install a new coil.
Magnet controller board under PF most if not all of the 3 fuses will be blown. If the person you just bought it from just dropped in new fuses you'll get a handful of games in and POOF. Magnets no longer work and the RIPPER coil won't fire. You'll find 2 fuses on the power board (I think F5 and F9) will be blown as well. You can unhook the magnet power board and have the ripper coil work consistently or you can REBUILD the magnet board with 3 new with IRL540 MosFETs not to mention you need to add a .22uf capacitor across the clock signal and ground on the ICL chip on the magnet power board (known as auxillary power board).