In the wreckage, you've found a lightsaber that appears to have taken some damage (or perhaps it was just shoddily built to begin with). You turn it on, and it crackles and fizzles but the blade appears. Oh wait... Yep, it's back - there it is. Let's cut up some clankers!

As the GM, I want to represent to the player that there's definitely something wrong with this weapon and that it may not be the most reliable lightsaber around. It also may not be particularly safe... But hey, it was free right?

Should I, as far as mechanics go, simply upgrade some of the difficulty dice to Challenge dice until such time as the lightsaber can be fixed? And if so, upgrade once? Twice?

What seems reasonable for a faulty, and possibly dangerous, lightsaber?

The Cortosos staff has rules for shutting down lightsabers in combat. Just have the faulty lightsaber use those rules on any target.

After some table discussion with my GM when he did the same thing (but his original idea was AWFUL), we settled on the Lightsaber both upgrading the difficulty on attacks once, and it generates an automatic Threat. I'd say that if you are using a saber from F&D that hasn't been upgraded you could skip the auto-Threat--it made more sense when handing out the one from EotE.

You could implement the rules that was used by FFG before.

Essentially after the lightsaber is switched on, you have to roll a force die, when a single Dark side point is rolled it gets reduced stats (from EotE/AoR normal lightsaber stats/fully modded Illum stats to only 7 damage, Crit 3 - no other item qualities like Sunder). And on a double Dark side point roll, it just shuts down for the encounter.

Yeti's idea is also pretty decent.

But regardless, I'd keep the reason the lightsaber is busted is more because of the crystal itself than anything - makes it so it's harder to replace as opposed to just throwing down the 300 credits and doing a mechanics/lightsaber check to repair it like any other normal damaged item.

Narratively for the first one you can say the crystal is just too old and can't focus energy as well anymore, for something like Yeti's you could say it's emitting too much energy and it makes the lightsaber harder to control (for either you could also require credit sinks to up the power the lightsaber hilt pushes through or repair constant damage to the hilt from the crystal).

Add Inferior and/or the Cortosis staff/gauntlet effect as Rakaydos suggested.

There are also existing rules for damaged gear, I don't know the page number in the FaD beta, but in Eote/AoR it's on page 158-159 and 172 respectively.

Jewel of Yavin has an NPC with a faulty lightsaber, requiring them to roll a Force die each round to see if it shorts out.

Easiest method would probably just be to use the rules for "damaged gear" with the PC having to spend time and credits as well as making Mechanics checks to fix the hilt, depending on how damaged it is. And should the player roll a Despair, then the lightsaber shorts out and moves one step down the "damaged item" track until it's destroyed.

Of course, they could always just pop out the focusing crystal and slot it into a brand new hilt, which would cost 300 credits and not require any skill checks beyond the one to track down the new hilt in the first place.

All excellent ideas! Thanks.

Yeti, I'm curious, what was your GM's original idea that was so awful?

I believe I'll go the "damaged gear" method for the hilt itself. It is moderately damaged. So it can be fixed at a price of ~150CR. Replacement parts are Rarity 5. Until it's fixed, as per the maintenance rules, the user can add an extra difficulty die to its use.

Unfortunately, the damage goes a bit deeper than that. The hilt can be maintained (or even replaced), but the crystal is cracked. It cannot be fixed; it has to be replaced. As long as the cracked crystal is being used, difficulty is upgraded once.

With a rolled Despair, I can do a couple different things. I can give it the "refined cortosis staff" treatment and shut the blade off temporarily. I can cause the hilt to become damaged again. I can make the crack worse, causing another difficulty upgrade....

Taking a cue from a long time ago product, an immitation LS, iif the faulty LS comes into contact with a blaster bolt or another lightsaber (via the parry or reflect talent) it also shuts down. The use of Parry/ Reflectr would still be effective, just has an additional complication.

This would be alot in combination with some of the other suggestions, but take what you want. Leave the rest.