HP (Hewlett-Packard) HP 85660B ユーザーズマニュアル

the output of 

 is high, and CR12 is reverse biased. If the dc input voltage to the

 V supply is greater than 

 V, then the voltage at pin 5 of 

 is greater than

 V, and the output of 

 is high. This turns on transistors Q13 and Q7, pulling

the collector of Q7 to about 

 V. This provides the HPUP signal.

If any of the above conditions are not met, HPUP remains low. R59 and Cl4 provide an

additional time delay at turn-on to allow the supplies to settle down.

For location of hardware and cables referred to in this procedure, see Figure 1.

Remove ac line cord from both instruments before proceeding with this
procedure.

1. Position instrument upside-down as show in view A.

2. Remove feet   from rear of RF Section by removing screws   show in view A.

3. Remove bottom cover by loosening screw   and pulling cover toward rear of instrument.

4. Location of fuses is shown in view B.

Figure 1. Internal Fuse Placement

A l 7   3