Sect. IV Page 6 Model 412A
lOj Replace lamp in light-beam chopper and re- 2) Remove three leads connected to demodulator.
move upper lamp nearest rear of instrument. This
lamp illuminates rear section of demodulator. 3) Remove nuts from demodulator mounting screws
and remove demodulator from instrument. If you
11 j Connect common ohmmeter lead to demodu- must get at screw heads to remove nuts, remove
lator terminal which has the brown-orange lead four mounting screws from light-beam chopper
connected to it. assembly (Figure 4-8) and let assembly hang by
its leads.
12) Connect other lead from ohmmeter , the
terminal which has the white-orange lead con- Reverse the above procedure to install replacement
nected to it. assembly. Be sure to connect pink-orange lead to
terminal nearest instrument rear, white-orange
13) Plug instrument into power source, turn it lead to center terminal, and brown-orange lead to
ON, and note resistance indicated on ohmmeter. terminal nearest front of instrument.
Typical resistance is bctwecn 1 meg and 2 megs.
14) Turn instrument off; replace lamp and V102.
4-12 CABLE REPLACEMENT
Figure 4-3 is a connection diagram for the VOLTS,
4-11 DEMODULATOR REPLACEMENT MA/OHMS, and COM cables. Replacement of the
VOLTS and MA/OHMS cables is straightforward:
Check with your @ Representativeabout a replace- connect the new ones as indicated in the figure.
ment demodulator. However, be careful when replacing the COM cable.
The position of the leads on terminal post #3 is
1) Turn instrument off. critical. Connect the leads as shown in detail.
DETAIL OF
TERMINAL POST # 3
-ACCESS HOLE
1
MA OHMS COM VOLTS
(3 CONDUCTOR) (2 CONDUCTOR) (2 CONDUCTOR) LD - L - 261
Figure 4-4. Connection Diagram for Volts, MA/OHMS and COM Cables |
ACEC
