Far as I know, it should be a fast blow ...

SloBlo could require up to twice the current flow before it fails, and those are really teeny tiny traces ...

There is a problem in this area as the Williams repair manual http://www.planetarypinball.com/reference/partsmanuals/WMS_Parts_Green_16-9932/index.html#/38/ clearly lists this as a slow blow, but there are many operator manuals that say it's a fast blow. I would say put in a fast blow and run display test, if it doesn't blow you are golden. If it blows during test, consider changing it to a slow blow. Eventually you are going to have to replace the original plasma display, likely with a newer low voltage display like a color DMD or LED display; after you do that, just pull 601 and 602 off the board and throw them away since the HV section of this board will no longer be needed.

If you do pull the fuses, you want to also tag the board to say why there are no fuses as a reminder to yourself, or for the next guy if you decide to sell the pin.

If fast-blow do not blow, leave 'em.

The thing about plasma displays is that when they degrade their resistance goes up and the current drawn out of the supply goes up too. That can damage the drivers. You can tell when it's happening if you're paying attention but a lot of people don't......

If you're going to pull the DMD and replace it with a LED or panel then you might not care, but if not, well.....

FWIW I have two games here that are both Williams DMD units with OEM displays and a third that's a Sega. All three are fine and within tolerance and one was a commercial game before it wound up here. I'm rather surprised, honestly, but pleasantly so that the displays have held up as well as they have.

The plasma displays are all going to fail sooner or later ... that's just entropy at work.

That being said, there are displays 20+ years old that work just fine, and may continue for years to come.

But NEW ones? the lead in the glass will eventually cause production to cease forever.

In my case, I keep the displays removed for ColorDMD replacements, and they're spares for my other games now.

The most important thing, however, is to make sure your power supplies are in good shape. A properly functioning power supply will keep a display running for a good long time.

A malfunctioning power supply will destroy a perfectly good display in a very short amount of time.

Check your DMD boards for signs of burning, etc ... if you've never done a DMD kit, it's probably time to do so.

Always mount the parts about 1/8" off the surface of the PCB when doing a kit, to ensure airflow above and below for proper cooling.

Either work fine. The specification was changed somewhere along the line. Throw in fast blow if you are concerned - they will blow sooner if there is a problem.