Diode across the coil faulty?

Incorrect fuse size (value)?

Coil terminal intermittently touching the metal frame or bracket holding it?

If the diode was open circuit it's possible.

The 'special' solenoids:

Left kicker
Right kicker
Left Jet Bumper
Lower Jet Bumper
Right Jet Bumper

Can activate and hold on until a fuse blows.

Check all the switches here, make sure the switches can't get stuck on, and that they have a good gap when not activated.

When you first turn on the game, do some coils pull in before the game get's booted up?

Play a game or two with the glass off. Can you see the slingshot kickers, holding in? Jet bumpers holding in?

With the glass off I can generally hear if a coil is solidly on and holding in too long. It makes a very distinct buzzing noise.

On most boards of this age there has been work done in the upper right corner where these coils are controlled. Even if the switch isn't holding the coil on, bad parts in the Special Solenoid area can cause problems. If a 7402 chip is already in a socket, make sure it is a 7402, not a 74LS02 or something with letters in the middle of the number. Board problems here that don't immediately lock the coil on and blow the fuse immediately will usually make the coil warm/hot to the touch.

Immediately when the fuse blows, open the playfield and feel all the coils. If anything is hot to the touch, consider checking that coil very carefully for the switch that activates it, and the parts on the board that activate it. Consider replacing the coil if it's hot to the touch.

The coil solenoid is 2 1/2 Amp.

I have had some games that used a fraction more power.

In general, you shouldn't overfuse.

The fuse is there to protect your machine from burning up lots of parts. If you overfuse, you might have a small problem turn into a problem that involves a lot of burnt up parts.

However... I have had a couple of machines that a 3 Amp fuse here saved me having to go out every week or two to replace the coil fuse.

Let us know what you find, and check what pins4u said above, and do that first. Great troubleshooting advice!

Remove the apron. Check the outhole coil. Remove it and see if the wrapper is worn possibly rubbing on the bracket. Do same with knocker coil. Aside from that above comments on special solenoids.

Differentiate "power on" from "game start". Entering diagnostics is equivalent to game start.

• If a solenoid locks (or a fuse blows) on power on then you most likely have a shorted drive transistor.
• If a solenoid locks (or a fuse blows) on game start then you most likely have a stuck special solenoid trigger (playfield switch) or a fault in the special solenoid logic level circuitry.

Then it is not likely to be the drive transistor.

So is there a locked on solenoid or just a fuse blow? If you can hear a solenoid locking on then examine the trigger. If you cannot hear a solenoid locking on then check the resistance of all the special solenoids. If there is a shorted solenoid there will be no magnetic field generated (no audible sound of a plunger) but the current will still flow without any resistance and the fuse will blow.

If you disconnect both the trigger connector (1J18) or the drive connector (1J19) this will deactivate the special solenoids and they just won't work. If they don't work then you won't blow a fuse.

Note that there is no software control for the special solenoid drive. The special solenoids can only be activated by the trigger. Look at the trigger switch not the score switch. The score switch is connected to the switch matrix and does not control special solenoid activation.

With what you've described, everything points to a problem with the triggers but there could be multiple problems masked by the obvious problem. You will only discover if there are multiple problems if you deal with each problem that arises that may be masking the other problems.

While the broken cap doesn't help the sling's performance it being disconnected would not cause the lockon. The cap is there to impart a minimum pulse to the circuit so that even a short hit can fire the sling. With it missing, a longer pulse from the switch will be needed. (The circuit only fires as long as it gets a signal).

Now a defective cap that's shorted might fire once and lockout but since 1/2 of your cap isn't connected....

Whoot!

Good catch!

Congratulations!