HP 54121A Service Manual page 255

PrOCBdure Part l: Determining R in the ohm's law formula I = E -i- R
1. Turn mainframe's front-panel power switch to STBY.
2. Place DMM in four-wire resistance measurement mode.
3. Connect one end of alligator clip lead to (A3) TP2.
4. Connect both positive DMM leads to other end of alligator clip lead.
5. Connect both negative DMM leads to ground point TP3.
Top-Rear Comer of Horizontal Control Assembly (A3) Top View of Mainframe's Card Cage
Front of Card Cage Assembly
6. Record resistance readii^ in steps 12 and 14 (2 places after the decimal are
required).
Example: 200.06 ft. Leave DMM connected across A3R46.
Part 2: Determining E in the ohm's law formula I = E 4- R
7. Disconnect the ribbon cables which attach to the rear of the horizontal control
and ADC assemblies.
8. Change DMM to make voltage measurements.
9. Short Horizontal Control assembly (A3) test point TPl to TP2.
10. Turn mainframe power on, and set timebase delay to 16 ns.
11. Record DMM voltage reading in step 12 (5 places after the decimal are
required).
Example: -1.00039 V.
HP 54120B
Service Manual
Adjustments
4-5