Teledyne 4020 - Hydrocarbon analyzer - Manual (Page 15)

Total Hydrocarbon Analyzer
Teledyne Analytical Instruments xv
3. External hazardous voltages which may be
connected to the Model 4020 alarm relay
connections.
Procedure for Removal of Internal Inaccessible
Shock Hazards
CAUTION: SERVICING OR MAINTENANCE OF THE 4020
SHOULD ONLY BE DONE BY SUITABLE TRAINED
PERSONNEL. TO AVOID THESE INACCESSIBLE
HAZARDOUS VOLTAGES WHEN SERVICING THE
4020, PERFORM EACH OF THE FOLLOWING STEPS,
IN THE ORDER GIVEN, BEFORE SERVICING
BEGINS:
1. Switch off the power to the 4020 and remove the mains (line)
power cord from the 4020.
2. Remove all external voltages from the connections to the
alarm contacts.
3. Wait one minute.
4. Discharge the anode supply voltage.
a. Connect one end of an insulated (to 1000 VDC or more)
clip lead to 4020 chassis ground (the standoff for the
upper right corner of the mother PCB).
b. Put one end of a 500V rated 1000 ohm resistor in the
other end of the clip lead.
c. Check the voltage between chassis ground (the standoff
for the upper right corner of the mother PCB) and the top
side of R2 at PCB number B74671. It should be between
-5VDC and +5VDC. If is in that range, the inaccessible
hazardous voltage removal procedure is completed, if not
repeat steps 4.a and 4.b.
If it is absolutely necessary to work inside the instrument with power
on, use the ONE HAND RULE:
Work with one hand only.
Keep the other hand free without contacting any other object. This
reduces the possibility of a ground path through the body in case of
accidental contact with hazardous voltages.