Model 11 153A Section V
5-1 7. Most reeds on the ac converter assembly are soldered 5-23. Some reed relay failures will cause little or no
in place, while A7K9, 10, and 11 are inserted into spring noticeable symptoms in ac measurements:
clips. The special reed replacement tool, -hp- Part No.
4040-0720, provided with the 3484A may be used to A7K3: If this reed is shorted, the symptom will be low
remove and replace reed switches which use the spring clips. readings at 100 kHz and higher on the 100 mV and
Use of the tool is illustrated in the 3484A Operating and 1000 mV ranges.
Service Manual.
A7K1, K2, and K1 1 : If any of these reeds are shorted,
51 8. THERMOCOUPLE REPLACEMENT. there will be little, if any, degradation in the
operation of the 3484A in the AC functions. The
When the thermocouple A7TCl requires replacement, symptom will be low input impedance in the DCV
mode. Table 5-5 in the 3484A Operating and
resistors A7R112 and A7R140 must also be replaced. These
resistors are matched and supplied with the replacement Service Manual lists the symptoms and causes of
this type of failure and other failures which will
thermocouple. Check the Thermocouple Protection Circuit
using the procedure outlined in Paragraph 5-26 before primarily affect the DCV mode of operation.
replacing the thermocouple. It will also be necessary to
perform the Adjustment Procedures, Paragraph 5-7, after
524. INPUT AMP. BIAS ADJ. RANGE.
replacing the thermocouple.
5-19. AC CONVERTER ASSEMBLY EXCHANGE. If A7R42 cannot be adjusted to the proper value in
Paragraph 5-10d, and the circuit appears to be operating
correctly in other respects, it may be necessary to readjust
A factory rebuilt and tested converter assembly, -hp- Part the range of A7R42 as follows:
No. 11 153-69501, may be purchased on an exchange basis.
Contact your nearest -hp- Sales and Service Office, listed in
Appendix B, for exchange details. a. Replace jumper wires numbered 1 , 2, and 3 (adjacent
to A7R39,40,41) if cut.
5-20. TROUBLESHOOTING. b. Measure voltage between A7TP1 and input LOW, and
adjust A7R42 for most negative voltmeter reading .
If the True RMS Converter operates incorrectly and the
trouble cannot be corrected by the Adjustment Procedures, c. Cut jumper wires indicated in Table 54 according to
voltage at A7TP1.
Paragraph 5-7, the following troubleshooting information
should be used to locate the source of trouble. Check for
loose'wires or other obvious sources of trouble, such as d. Adjust A7R42 for voltage of 0 k 100 pV.
burned or loose components. Make sure that reed leads are
not shorted to adjacent components, and that the flex cable Table 54. Input Amp. Bias
is properly seated in the connector. Also, be sure the
3484A is operating properly in the DCV mode before I VoltageatA7TPl I Cutjumper:
attempting to troubleshoot the ac converter.
0 to- 7.0mV none
-7.0 to -1 3.0 mV 1
-13.0 to -18.9 mV 2
-18.9 to -24.8 mV 12
-24.8 to -30.6 mV 3
BEFORE WORKING WITHIN THE -30.6 to -36.2 mV 1.3
-36.2 to -41.8 mV 2.3
3484A, REFER TO PARAGRAPH 5-14, 41.8 to -48.0 mV 12.3
CLEAN HANDLING TECHNIQUES.
DIRT OR CONTAMINATION IN THE
INTERIOR OF THE 3484A MAY DE- 525. POST AMP. BIAS ADJ. RANGE.
GRADE PERFORMANCE.
If A7R70 cannot be adjusted to the proper value in
5-21. REED RELAY CHECKS. Paragraph 5-lOf, and the circuit appears to be operating
correctly in other respects, it may be necessary to readjust
5-22. Many cases of reed relay failure will produce notice- the range of A7R70 as follows:
able symptoms in the front panel display, such as very
inaccurate or overload readings on some ranges, no response a. Replace jumper wires numbered 12 and 13 (adjacent
to input, noisy readings, or incorrect response time. Failure to A7R141 and 142) if cut.
of a reed to operate properly may be caused by failure of
the reed switch, the reed coil, or the reed drive circuit. A b. Measure voltage between A7TP2 and input LOW, and
reed relay troubleshooting procedure is given in Table 5-3. adjust A7R70 for most positive voltmeter reading.
5 -7 |
ACEC
