Guildline 6634A Resistance Standard, Operator'S Manual

Page: 18 / 22

Section 4
OM6634A-B-02
4 January 2019 4-4
DEVICE VOLTAGE READINGS (Pl-7 Common)
HEATER ON HEATER OFF
E B C E B C
Q101 -3.05 -3.2 -5.2 -3.05 -3.2 -5.2
Q102 -5.4 -5.2 -3.05 -5.4 -5.2 -3.05
Q103 -2.95 -3.05 -5.3 -2.95 -3.05 -5.3
Q104 -1.4 -2.0 -1.45 -----------Variable--------
Q105 -0.75 -1.42 -1.45 -----------Variable--------
Q1 0 -0.75 -0.25 0

-0.25
-12.8
Table 4-2: Transistor Voltages
4.3.3. Over Temperature
If the temperature within the constant temperature chamber exceeds 34 °C

3

C, then
the OVER TEMP indicator will be lit. Allow the enclosure to cool to less than 30 °C.
Check the resistance of R2 (2.2

). Check between P2-F and P2-H to ensure that the
temperature sensitive switch S2 is open. If these conditions are satisfied, then replace
fuse F1 and check that the HEATER indicator is lit. Monitor the increase in temperature
with the PRT. If the lamp does not indicate heater cycling when the temperature
approaches normal, then check the operation of the control circuit as follows:
- Locate pins A and C of P2.
- Short pin A to pin C. The HEATER indicator should go out. If it does, then
check the resistances of RT1 and R1 as detailed in section 4.3.2. Replace them
as a matched pair. If not, then check at TP1 and TP2 with an oscilloscope
(common to P1-7). With P2-A and P2-C shorted, there should be no
oscillation. Check the voltage at TP3. It should be zero. Refer to Table 4-2
for voltage measurements to aid in locating the fault in the heater driver.