U13 on which board? And what problem were you changing it for?

and what game?

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With all you are having issues with, reseat this ribbon cable and be sure that it is not off by one row and you have no bent board pins.

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Its very uncommon to blow a pair of fuses with a single failure; as PinballManiac40 was mentioning, having a data cables hooked up wrong can cause weird problems; however, when I see two HV fuses go at the same time I immediately think that something is mis-wired.

Lets say at some point i the games history, someone accidentally connected one of the high power coils under the playfied to the low power source, or the either way around...it doesn't matter which as in either instance this would create a bridge between the two circuits and half the combined current of the high and low power solenoids would flow through each fuse and everything will operate perfectly...until there is a malfunction which would then cause BOTH fuses to blow.

The check is simple, remove both fuses and check the resistance between the fuse holders on the load side...there should be no continuity between them, if there is then correct this before you continue troubleshooting.

If this checks out AND the ribbon cables are all on correctly, pull your CPU board out, place it on a hard flat surface and press down firmly on the ASIC to make sure its fullt seated in its socket; I personally do not recommend doing this in the machine as the ASIC has no support and the very thin traces on the PCB can crack when the board is flexed.

The side closest to the connectors.

This is correct, all three 50V circuits are derived from the same source.

Yes on the source side as these are physically connected together on the power board

No on the load side, these are the three individual circuits that leave the power driver board and each is independently fused; there should be no connection between these circuits with the fuses removed.

Sometimes you can visually follow the traces to see what connects where. The line side is common and the load sides are separate (or should be).

It is really helpful having a manual with the schematics for helping to understand what goes where.

These are my favorite threads as we have helpful pinsiders with good approaches.

Very true,
This will help:

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Start the machine with the coin door open. Once it boots up, close the coin door. If it doesn’t blow the fuses, it could be a transistor on one of the boards affecting the blanking circuit.

When you power it on, the D19 led on the MPU should illuminate for a few seconds and then go out. If you don’t see D19 light up, that’s the issue you need to start tracing.

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I would try flipping over the small ribbon cable between the CPU and Power board. I've actually never ran into an issue where the blanking signal doesn't do its job.

Do you still have the sound board plugged in with no processor?

I have. My new Rotten Dog auxiliary driver board had a bad transistor that caused the blanking circuit to be inoperable. Powering the machine on caused F103,104 & 105 to blow randomly.

@Biglouie, did you resolve your issues?

What did he do that stopped f104 and f105 from burning up on start up?

Games can have unique occurrences from one to another. Best to start your own repair thread if you have a game with an issue.

I repair my own games, but I like to see every repair thread closed with a resolution.

I had an issue that was nearly identical to this recently with my Fish Tales. After reseating the ASIC chip, the game rom, and 1 other (socketed) chip on the CPU, problems vanished!

I have been working on games for over 10 years. I don't see reseating ICs that wll be a cause for fuses to blow, but rather just plain boot up issues.

Now if you said you reseated ribbon cables, in that case, I can believe that. If you plug in certain ribbon cables one row off that will definitely cause fuses to blow.

I definitely reseated the ribbon cable, in practically all the (6) locations several times even before reseating the IC’s and it never corrected the issues I was having (which was more then just fuses). Maybe I screwed up the ribbon cable over and over, or Wth? Don’t know. All I know is the game has been working no problems and that occurred over a month and about 200 games ago.