I would swing that board open and see if all the non-functioning lamps are on the same wire, then look for a break in that wire.

I still have a similar problem on my Pinbot. I don't have a solution, but it was tied to adding LEDs. I /did/ cut the resistors for what it's worth to put the other LEDs in.

When you checked these 4 fuses, did you pull them out to test? They will always test good while in the holder even when burnt.

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You can fix this problem in about 2 minutes without messing with boards or fuses. If you already switched the bulbs to LEDs, they take much less power, like 80% less power. This means that you can run many more lights over an existing circuit. If you were to simply jump the grounding wire between the working and non working light stream with a replacement wire of virtually any type, to include speaker wire, the lights will instantly come on and be just fine. When I (briefly) had my pinbot I got the lights working on the right side of my machine by jumping the ground wire between them. Note this will ONLY work if you have switched out incandescent to LEDs. Doing this with incandescent WILL blow a fuse. You want to jump the lines stapled to the backbox as depicted in the image.

Edit: This of course assumes that checking the fuse, and the connector to the power board does not work.
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There are 3 different voltage type bulbs in Pinbot. You are working on the 6 volt bulbs which need no modifications. If you decide on replacing the #1251 and #89 flash bulbs just ask and l will show you how. Thank you very much for the donation.

Playball!

Ok, for #89 bulbs (12 volts) there is a resistor board in series with a single bulb or a pair of parallel bulbs to drop the voltage from 24 volts to 12 volts with a large resistor (red arrow). Picture of resistor board below. The resistor board also has another resistor (warming resistor marked with a green arrows) in it's circuit to run a small amount of current thru the bulb to preheat the filament so that the bulbs flash brighter and last longer. Since Leds require only a small amount of current to light, the current going thru the warming resistor will be enough to light the Led bulb constantly. So to address this issue there are 3 different ways to correct this, first is that you can unsolder the black wire from the resistor board and add a small wire nut to insulate it. This will cut the current path to ground. Second is that you can find the pair of bulbs that flash together and replace only one of the pair with an Led bulb, the other bulb will dissipate the warming current and keep both bulbs off. The third method is to unsolder one lead of the warming resistors and lift it away from the board thus breaking the circuit stopping current flow. Each resistor board is 2 separate circuits and can control 2 pairs of flash bulbs. Let me know if you have any questions so far.

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If you have 2 black wires on the resistor board, make sure that you twist them back together after removing them and then install a wire nut. This must be done to all resistor boards. Then you are ready for #89 LEDs.

Pinbot has resistor boards in the back box and under the playfield.

Now if my memory serves me correct there are 8 #1251 bulbs in Pinbot. There are 2 in the insert board 2 on top of the playfield and 4 under the playfield. #1251 bulbs are 24 volt bulbs and don't have any voltage dropping resistors in series with them. Your options for using Leds are, buy 24 volt Led bulbs, add a dropping resistor in series and use a #89 bulb instead of the #1251 bulb. Or rewire them from parallel to series and use #89 bulbs. If you can solder ok then I would recommend rewiring them in series because there are more colors and styles of #89 12 volt bulbs then #1251 bulbs, and there are cheaper to buy. Let me know which way you want to go.

So when you turned on the machine you heard a louder then normal hum. This was a short on the GI circuit that blew the fuse. You are using #44 LEDs in the insert board. Either one of the LEDs is bad or when you installed one of the bulbs into the socket it caused a short. In the future look into the socket for strands of wire, solder or small nuts and screws before installing the new bulb. I have seen about everything in my time working on machines. Shorted sockets don't happen much on #555 bulb sockets but #44 can sometimes be a pain. Anyway try installing them again and see what happens. The 2 #89 bulbs are on a different fuse so it didn't have anything to do with them.

I think you are referring to the computer controlled lamps. I don't like to make this type of call because either work fine. It's a matter of taste. Now for the GI lamps it reduces the power which will make the connectors last longer. A very good idea. Lamp sockets generally don't give any problems until you mess with them. LEDs will last a lot longer so you don't have to do as much maintenance in the future. But it's your call on what looks good to you.