HP 712B Operating And Servicing Manual page 20

TROUBLE SHOOTING CHART
The following information is designed to aid in trouble shooting a defective instrument:
SYMPTOMS
Instrument NOT
operating, pilot
light NOT on.
Instrument NOT
operating, pilot
light ON.
POSSIBLE CAUSE
Line fuse Fl blown
due to defective fuse
or overload in either
power supply.
Defective tube or
component causing
improper operation.
TEST PROCEDURE
Replace fuse.
If this fuse blows, re-
move tubes VI, V2, and V7, and again
replace fuse Fl. If this fuse blows,
it indicate s:
1. Short circuit in wiring associated
with power transformer T2 or T3.
2. Short circuit in filament wiring.
3. Transformer T2 or T3 is defective.
If fuse does not blow when rectifying
tubes are removed, it indicates:
1. Defective filter capacitor.
2. Short circuit in a tube.
3. Short circuit in the direct current
wiring.
To localis e the circuit in trouble,
measure the DC resistance across the
output from each of the three recti-
fiers. Disconnect the instrument from
the power line before making the mea-
surements.
Normal DC Resistances Across Power
Supply Circuits:
Recti- Connect Ohm- Approx.Normal
fier
meter Across Resist. (Ohms)
VI, V2 Socket pin 8, 50K
VI or V2, and
term. COM
V7 Socket pin 8 2M
V7, and term.
-300V 50 MA
SRI Terms. of 1.5M
capacitor C9
(connect meter
neg. lead to
junction of C 9
and R13)
Set METER RANGE switch at 0-150V
-BIAS and turn -BIAS CONTROL to its
maximum clockwise position. If volt-
meter on control panel does not deflect;
or reads les s than 150 volts, trouble is
in bias supply circuit. Check bias sup-
ply DC voltages against those indicated
on schematic diagr am (should agr ee
within ±10%).
4-8
REMEDIES
1. Locate and clear
short circuit.
2. Locate and clear
short circuit.
3. Replace defective
transformer.
1. Locate and replace
defective capacitor.
2. Locate and replace
defective tube.
3. Locate and clear
short circuit.
Locate defective com-
ponent, and replace.