Troubleshooting Tree - HP 5334B Service Manual

WARNING
DO NOT OPERATE THE OVEN CIRCUITS WHEN THE OVEN MASS IS
OUTSIDE OF THE OSCILLATOR INSULATED HOUSING. DOING SO
WlLL OVERHEAT THE OSCILLATOR CIRCUITS INSIDE THE OVEN
MASS AND CAUSE PERMANENT DAMAGE. ALL OVEN TEST POINTS
ARE AVAILABLE WITH THE OVEN MASS AND OVEN CONTROLLER
CIRCUIT INSIDE THE HOUSING.
WHEN OSCILLATOR COVER AND INSULATOR ARE REMOVED, THE
THERMAL FUSE WlLL NOT PROTECT CIRCUIT FROM OVERHEATING.
APPLY OVEN POWER ONLY WHEN ACTUALLY MAKING MEASURE-
MENTS FOR TROUBLESHOOTING OR AS DIRECTED IN
TROUBLESHOOTING TREE, FIGURE
8-10.
8-407.
Troubleshooting Tree
8-408. Figure 8-10 is a troubleshooting tree for the oven circuits. The troubleshooting procedure separates the
different functional circuits by monitoring the oven supply current during different operating conditions. For ex-
ample, if the warm-up current is excessive, this indicates a problem in the warm-up current limit circuit, or the
current control and heater circuit. If shorting the thermistor reduces the current being drawn from the power
supply, this indicates the current control circuit is operating and the problem is most likely in the warm-up cur-
rent limit circuit.
8-409. As with most troubleshooting trees, this is intended to be a guide to the trouble area. It is not a sub-
stitute for technical skill in isolating the faulty components.
8-410. Table 8-11, Oven Circuit Voltages, gives normal circuit voltages during warm-up, operation, and when
thermister RT1 is shorted to ground. Use this table during troubleshooting.
8-41 1.
Troubleshooting Cautions
8-412. When oven current is excessive, turn on the power supply only long enough to make the necessary
measurements. Do not leave power on if the oven is drawing excessive current. With the housing cover and foam
insulator removed, the thermal fuse, F1, cannot protect the circuits in the oven mass from overheating and
damage.
8-413. When power is applied to the oven controller circuit, it will go into its full warm-up mode. In this mode,
the maximum heating power is applied to the oven mass. The oven mass is a metal casting surrounding the oscil-
lator circuits and crystal. The OVEN MONITOR output will be approximately 1.5 volts below the oven power
supply voltage. In about 10 minutes, the oven will have heated to the proper temperature. The oven contoller will
begin to regulate at this temperature and the OVEN MONITOR will drop to approximately 3.5 volts. It is nor-
mal for the oven temperature to drop momentarily to a low value when the temperature first reaches maximum.
This lasts less than a second and is a typical circuit action.
HP 5334B
-
Service
Manual
8-60