Figure 6 Lisa/Mac XL power supplies external views. 1.8-A Lisa 2/10 to Mac XL power supply (left), and 1.2-A Lisa 2/5 power supply (right) are both marked "l 5OW," but the 1.2A model is actually a dual voltage model, and it's 50% stronger!

x 1.8 A = 216 W (44% over specification). Substituting Lisa 2/5 power supply values: 120 V AC x 1.2 A - 144 W (4% under specification).

So how can both models be marked 150 W? The acceptable input voltage specified in the Lisa 2 literature is 90 V AC to 130 V AC. Substituting 90 V AC (the low limit) into the Lisa 2/10 to Mac XL supply's formula (90 V AC x 1.8 A) lowers its relatively high rating to 162 W. Substituting 130 V AC (the high limit) into the Lisa supply's formula (130 V AC x 1.2 A) raises its relatively low rating to 156 W. Since both figures exceed 150 W, that presumably explains the identical ratings. Nevertheless, the Lisa 2/10 to Mac XL supply is notably superior.

When the original 1 .2-A Lisa 2/5 supply is used with an internal hard drive and a Macintosh XL Screen Kit (described at the end of this chapter), audible transformer ringing results, horizontal retrace lines become noticeable, and a slight screen flicker is introduced. Installing the 1 .8-A Lisa 2/10 to Mac XL supply eliminates all of that.

The 1.8-A Lisa 2/10 to MacXL supply is also a dual voltage model. 110 to 220-V AC conversion is made by moving two jumpers at the bottom of the board, as shown in Figure 7.

These differences make a very important point. If you only remember one thing from this: Always confirm specifications by making your own calculations.

Figure 7 Lisa 2/10 to Mac XL power supply-1 10- to 220-V AC conversion (1.8 A model only) is made by moving two jumpers at the bottom of the circuit board.

The card cage is a removable rack for the Lisa's circuit cards. It's also held by tight-fitting tongue and socket connectors. To remove it, disconnect all peripheral cables from the back of the