Varies (see Description)
BattleMech Manual (p. 87)
An energy weapon is insufficiently shielded and causes interference with other delicate electronics. The turn after the weapon has been fired, the following equipment aboard the íMech will not function: any ECM, any Active Probe, Artemis IV FCS, Artemis V FCS, Blue Shield PFD, any C3, Chameleon LPS, Cockpit Command Console, Electronic Warfare Equipment, MASC, MRM FCS, NARC, Null Signature System, Stealth Armor, Streak Launchers, Supercharger, Targeting Computer, and Void Signature System.
Alternatively, this quirk can be purchased for the íMech itself, in which case the problem occurs whenever any energy weapon on the íMech is fired. The cost for this version of the quirk is 2 points, but can only be purchased if the íMech has more than one energy weapon.