HP SCR-1P Series Operating And Service Manual page 31

Table 5-3. Overall Troubleshooting
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SYMPTOM
P~OBABLE CAUSE
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tow or no output voltage a., ' Front panel meter defectlve.
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b. Serles regulator loop defective, : Refer to Para- ·
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graph 5-57, then. Table 5-4. ,
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Hlgh output voaage a. Front panel meter defective,
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Serles regulator feedback' loop ,
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b.
defective. ·Refer to Paragraph 5-57, then ''
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Table 5-5.
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Check operatlng ~etup for ground loops;
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H!gh rlpple a.
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b, Check reference and blas voltages (Table 5.,-2) for:
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excesslve rlpple.
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c: Supply crossing over to constant current opera-
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tlon under loaded condltlons, Check current
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limit setting or constan~ current comparator ~Lr-
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cult.
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Impro~er measurement technique (Paragraph 5~8). · Poor line regulation
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a.
b. Check ref:.rence voltages (Table 5-2).
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Poor load regu latlon
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a. Measurement technique (Paragraph 5-B).
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(Constant Voltage)
b. Check reference voltages (Table 5-2).
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c.' Check the regulatlon characteristics of zener
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diode VRl as follows:
(1) Connect dlfferentlal voltmeter across VRl.
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(2) Connect appropriate load reslstor (RL), given
ln Figure, 5-3, across (+) and
H
output terminals.
(3) Perform steps b through f of Paragraph 5-13.
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(4), If the d!fferentlal wltmeter reading varies by
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more than l0mV, replace VRl.
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d. Ensure that ~upply Is not ,current limiting. Check·
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constant current comparator circuit.
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Poor load regulatlon a. Check referenr.e voltag'ls (Table 5-2).
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(Constant Current)
b. Cl5, Cl6, CR21, CR22 leaky.
c. Ensure that supply Is not voltage llml\lng. Check
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constant voltage comparator circuit,
Oscillates (Constant
a, Selection of Rl3 (l'.aragraph 5-73),
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Voltage/Constant Current)
b. Check C4 and Rl4.
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C,·
Open sensing lead (tS).
Instability (Constant
a. Reference clrcult (Table 5-2).
Volta'le/Constant Current)
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b. Noisy voltage or current controls, (R2 or R9). ·
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' c, Stage Ql or QB defective.
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d. CRl leaky.
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e., Rl, RS, R42, R40, R41, Cl noisy or drifting.
5-10