HP 5890 SERIES II Service Manual page 171

13. At the rear of the instrument, disconnect the two heater element leads at the AC power supply
PCB.
14. From inside the oven, draw the heater leads through the opening in the rear of the oven.
15. Remove the old heater element from the oven.
16. To prepare a new heater, note that it must be matched to a specific line voltage. From Table
4- 1, verify the unstretched length of the replacement heater element, according to the line volt-
age of the instrument. Stretch the wire EVENLY to the indicated length and allow it to contract
back to an approximate 720 mm length.
Table 4- 1. Preparing Replacement Oven Heater Element
INSTRUMENT RESISTANCE
VOLTAGE (ohms)
120(1) 9.05(+/- 0.05)
220(2) 30.42(+/- 0.17)
240(3) 36.20(+/- 0.20)
17. Route the new heater through insulators so that its ends terminate at the connection locations
on the power supply PCB.
CERAMIC OVEN HEATER STANDOFFS ARE FRAGILE.
SCREWS WILL CAUSE BREAKAGE.
18. Secure the heater to its standoffs with two screws.
19. Secure the two heater standoffs to the shroud with screws.
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HEATER ELEMENT
CONNECTION TERMINALS
UNSTRETCHED STRETCHED
LENGTH (mm) LENGTH (mm)
136 975
180 1110
214 1185
OVER- TIGHTENING OF
SVC 5- 9
CONTRACTED
LENGTH (mm)
720
720
720