HP 400F, Руководство по эксплуатации и обслуживанию, Страница: 26 / 54

Section V 400F/FL
Paragraphs 5-43 to 5-51 and Tables 5-4 to 5-8
Table 5-4. Troubleshooting Guide
MALFUNCTION INDICA TION
Instrument will not operate on line voltage,
and
UNE ON lamp will not light.
Instrument will not uprange above 0. 3 volt, but
works on O. 3 volt range and below .
Instrument will not downrange below 1 volt, but
works on 1 volt range and above.
voltage at A2R8 cannot be properly adjusted.
No voltage at A2Ll.
Power supply output unregulated.
No ae output.
Instrument operates improperly with inputs above
100
KHz,
but works with inputs
of
lower fre-
quencies.
Instrwnent will not operate properly on
O.
1 mv
range.
Meter deflection on all ranges with no input.
Meter remains at zero with any input on any range.
5-43. Refer to Table 5-4 for a Ust
of
possible mal­
functions and their probable causes.
NOTE
All the voltage measurements in this
section should be made with the
400F /FL input shorted and the RANGE
switch set to 1 volt.
5-44. POWER SUPPLY.
5-45. Measure the power supply outputs at Jumper wires
{f1
and N2 for +26 v and -26 v respectively.
If
both
outputs are incorrect. first check the components in
the +26 v section of the power supply. because the
control transistor in the -26 v supply is referenced
to the +26 v output. Consequently,
if
the +26 v be­
comes uru-egulated, the -26
v
wUl also be unregulated.
Refer to Table 5-5 for a list of check point voltages
in the power supply.
Table 5-5. Power Supply Voltages
CHECK POlNT VOLTAGE
Emitter Q4 +26. 0 v ±l v
Collector Q4 +41. 5 v ±5 v
Collector Q6 +27. 5 v ±1 v
Emitter Q8 -26. 0 v ±1 v
Emitter Q9 -43. 5 v ±5 v
5-46. AMPLIFIERS.
5-47. Both the preamplifier and the meter amplifier
are internally dc coupled.
If
the dc voltages anywhere
in the amplifiers are incorrect, the amplifiers will
not operate properly. Measure the dc voltages in the
amplifiers at the check points listed in " Tables 5-6
and 5-7.
5-6
PROBABLE TROUBLE
Fuse FI open.
Relay A2Kl stuck closed. or A2K2 stuck open.
Relay A2Kl stuck open, or A2K2 stuck closed.
Impedance Converter Circuit (A2Ql. A2Q2 and
A2Q3).
Jumper wire Itl broken.
A2Q6, A2Q7 or Zener diode A2CR12.
A2R33 shorted.
Filter switch 82.
Range switch SI, wafer D.
A2Q15. A2Q16. A2Q17.
A2C38. A2C39, A2C40.
Diode A2CRl shorted (400F only).
or capacitor
A2Cl shorted (400FL only).
Table 5-6 Preamplifier Voltages
CHECK POlNT VOLTAGE
Source Q l
-
2. 3 v
±Q.
5
v
Drain Q l -17. 0 v :t2. 0 v
Collector Q2 - 7. 5 v ±Q. 5 v
Collector Q3 -21. 4 v :t1 . 0 v
Table 5-7 Meter Amplifier Voltages
CHECK POINT VOLTAGE
Emitter QI0
-
0. 64 v
:to.
1 v
Collector QI0
+
9. 20 v ±1. 0 v
Collector Qll
+
0. 97 v :to. 2 v
Collector Q12 +22.00 v :tL O v
Collector Q13 +11. 00 v :to. 5 v
Collector Q15
+
2. 30 v
±C .
5 v
5-48. METER BRIDGE.
5-49. Measure the dc voltages on the transistors in
the meter bridge and compare the readings with those
given
in
Table 5-8. Also measure the voltages at the
meter terminals. The meter should he floating at
approximately -9 volts ±1 volt with respect to circuit
ground.
Table 5-8 Meter Bridge Voltages
CHECK POlNT VOLTAGE
Collector Q16 - 9 v ±1 v
Base Q17 -17 v ±l v
5-50.
E T C H E D C I R C U I T B O A R D R E P A I R .
5-51. TheModel 400F/FLuses plated-lhrough. double­
sided, etched circuit I:x>ards. To prevent damage to
01795-1