Take the 1.6 amp slo blo fuse out and see what happens

Seems like it! You could also try to remove the 10 amp bridge rectifier fuse in case the bumpers or flippers are involved.

Look for a coil that stays energized but drops out when you cut the power.

You can put the score motor into service position and turn it by hand.

You can also try slo-mo video recording on your phone.

There is a jack you can move so the score motor is in service position.

Page 7 of the instruction manual.

I would look at score motor switches 1b and 2b. When you removed the 1.6 amp slow-blow fuse it should have removed everything from the 110 side. Since it is still blowing, maybe one of the other switches at score motor #1 or #2 are contacting the 110 volt wiring. Sending raw 110 volts into one or more your 25v coils.

A shorted DC bumper rectifier might be the problem. Its fuse is on the DC side, and will not help if rectifier is internally shorted. Try removing one of the AC leads going to rectifier.

Since probably only one of the 4 diodes inside the rectifier is shorted, it will short only one half of the AC sinewave input, causing DC current to flow through transformer 24VAC secondary, saturating the transformer core. That is why the 110V primary fuse blows before the 24V secondary fuse.

Very cool Tuukka . I'd like to understand this a little better so I grabbed the schematic:
Gulfstream rectifier short (resized).jpg
If I understand correctly one of the rectifier diodes has shorted so that it conducts presumably in both directions rather than the single direction it is intended to. If the red diode for example were shorted then the rectified DC output voltage on the -J- or jumper wire would short to the AC input voltage on the -RED- wire and eventually find its way back into the 24 volt secondary transformer winding. The extra DC current apparently isn't enough to blow the 15 amp fuse on the 24 volt circuit.

The steady DC current flowing through the 24 volt secondary winding would create a constant magnetic field in the transformer core that would combine with the normal alternating magnetic field created by the 110 volt AC input current in the core. The combined magnetic fields saturate the transformer core at some point. A saturated core essentially means that the core cannot support any more magnetic field. Once the core is saturated any current applied to the core doesn't go towards increasing the magnetic field but instead gets wasted as heat.

Once the core saturates the input 110 volt current isn't doing the work of creating more magnetic field. Does that make the saturated transformer core look to the 110 volt supply like a lower resistance (or actually lower impedance) load which draws more current which in turn blows the 110 volt 10 amp fuse?

/Mark

Yes Mark, you got it absolutely right!

Normally the transformer core has large inductance, reducing the power it draws from primary input, even though its resistance is low. Inductance causes the primary current and voltage to be in different phase regarding to each other, and thus the apparent power is low. That's why a transformer without load stays cool.

Now, if one diode gets shorted, that means one half of AC input gets shorted via the other diode in series with the shorted one, while the other AC half is still blocked by the other diodes. Because current then flows only during one half, that effectively means that current only flows one way through the transformer secondary. Each half-wave magnetizes the core a little more, and after a while it can't be magnetized any further - it is saturated. Then its inductance drops to much smaller value, allowing primary current to flow almost in phase with the primary voltage, making the power consumed in primary much larger - and blowing the primary fuse.

This is also why a half-wave rectified power supply needs to have a much larger transformer than what would be expected from the load current - it needs to withstand the DC current without getting into saturation.

There is a great online circuit simulator that can demonstrate this better than I can explain it but here are two screen shots:
Rectifier simulation (resized).jpg
On the left is a simplified version of the rectifier circuit with a 60 Hz voltage source representing the transformer and a 100 ohm resistor representing the various coils (e.g. pop bumpers) using the DC supply. Along the bottom you can see that the current through the voltage source is less than an amp and the voltage across the load is fully rectified. (Ignore the 1 ohm resistor on the bottom which was added to avoid a dead short in the simulation.)

On the right side the lower right diode of the rectifier is replaced by a wire to represent the short. In this case the circuit looks like the original circuit half of the time. But the other half of the time all of the current flows through the upper right diode of the rectifier, then down through the short on the lower right and back out to the voltage source. No voltage is generated on the output so the DC is only half rectified. The current through the voltage source is measured in amps, not in milliamps.

To see these animations and experiment with the circuit try these links:

Normal rectifier: https://tinyurl.com/y84jb78b
Damaged rectifier: https://tinyurl.com/y7kbqljs

Then click on the Run/Stop button in the upper right to start or stop the animation.

BTW, I wonder if the topic title could be revised to make the shorted rectifier discussion easier to find in the future.

Both are fine, since the voltage is only 24V, but get the 400V one, so it could be used in higher voltage circuits also if needed.