Hello everyone. Looking for some feedback on my Last Action Hero problem. Initially got the game with F6 and F9 blowing fuses. Isolated the problem to magnets being locked on. Rebuilt magnet board with IRL540n mosfets, replaced the 74HC273 IC, reflowed all the solder on the header pins.

Now I can not get any magnet activity, in test mode or during game play. At the magnet board, I have 4.69v, which I think is sufficient to operate the ic. I have 74v at the magnets. If i ground the metal tab on the IRL540n with a jumper wire, each magnet works.

Does this suggest the Pia 6821 pins 10-13 are not working? Is there a way to check the pia with a dmm at these pins?

To my surprise I had 2 logic probes in my tool box.

To test Pia 6821 at pins 10-13 this is what I did. (These are the pins I have read about in other threads that control magnets)

I went into test mode to the magnet test. Held down the start button to activate magnets then touched each pin 10-13. I got all low (0) readings. I assume this means that portion of the pia is dead.

I will socket and replace the pia and report back when it is done.

Bit of an update. Borrowed an CPU out of Lethal Weapon. I have pulses at 11b 6821 on pins 10-12 as expected.

Magnets are still not coming on. Grounding tab on IRL540N, do make the magnets come on.

I think this narrows the problem down to signals making it from CPU to magnet board. If they check out the last thing I can possibly see being the problem is that I used a 74HC273 instead of 74HCT273 chip on the magnet board.

That mod is factory.

I have upgraded the 3 transistors to IRL540N. I am thinking these mosfets (I think that’s what they are called) need the 74HCT273. The original board has the 74HC273 but uses transistors P20N10.

I did logic probe testing at the magnet board for all 3 orange wires. I get pulses during magnet test and pressing start button.

Update. Finally got in the 74HCT273 chip. When doing the magnet test in diagnostics you can hear the magnets pulsing but you can’t feel any magnetic pull through the playfield.

I took the magnet board to a GnR machines and it acts the same way. You can hear the magnets pulsing but there is no noticeable magnetism.

When the working magnet board from
GnR is tested, you can hear the exact same pulsing noises but they are louder and you can feel the magnetism.

I will now source some original spec transistors 20p10 and try those instead of the IRL540N

Solved.

It seemed the new IRL540N mosfets that were ordered initially were faulty. Ordered from another vendor and now the magnet board works fine.