Section V Model 11 153A
c. Cut jumper wires indicated in Table 5-5 according to h. Observe waveform at A7TP2 while changing 3484A
voltage at A7TP2. RANGE to 1000 mV. When range is changed to
1000 mV, waveform should be clipped at about 5 V
d. Adjust A7R70 for voltage of 0 f 500 pV.
peak-to-peak for approximately 1 second, then re-
Table 5-5. Post Amp. Bias. duce gradually to about 4 V peak-to-peak. A correct
waveform indicates that protection circuits respond
in the proper length of time.
0 to + 57.8 mV none 5-27. 1/10 SCALE ADJUSTMENT RANGE.
+57.8 to +108.3 mV 12
+I 08.3 to +I 56.5 mV 13 5-28, If the correct adjustment of A7R98 cannot be made
+I 56.5 to +206.0 mV 12.1 3 in Paragraph 5-1 1, Step d, it may be necessary to remove or
replace one or more of jumper wires A through G. These
526. THERMOCOUPLE PROTECTION CIRCUIT. jumpers are in the 14-pin IC socket as shown in the
component location drawing accompanying the schematic
Before replacing a damaged thermocouple (A7TC1), the diagram, Figure 7-2. Jumper A has the least effect on the
Thermocouple Protection circuit should be checked, using Converter Amplifier output and Jumper G has the greatest
the following procedure, which requires a test oscillator and effect, with the progression being approximately binary.
an oscilloscope. Removing a jumper decreases the output voltage, and
replacing a jumper increases the output. If all or most of
a. With the thermocouple A7TC1 removed from the the jumpers are removed, the amplifier output may go to
instrument, set 3484A FUNCTION to VAC(AC),
RANGE to 1000 mV. zero with 1 /lo scale input.
b. Adjust test oscillator output to 2.8 V at I kHz. 5-29. If either the Converter Amplifier A7IC1 or the
Thermocouple A7TCI has been replaced, it may be
c. Connect oscilloscope to A7TP2 and observe wave- necessary to perform the following procedure in order to
form. If waveform is a clipped wave approximately bring the adjustment into the proper range. An ac calibrator
5 V peak- to- peak, A7IC2 comparator circuit is is required for this procedure.
operating correctly under constant input condi-
a. Set 3484A FUNCTION to VAC(AC), RANGE to
tions. If not, troubleshoot A7IC2, its associated input 10 v.
circuit, and A7Q28, 29.
b. Adjust A7W8 and A7R123 fully clockwise.
d. If waveform in Step c is correct, install the thermo-
couple and A7R112, A7R140. (See Paragraph 5-18.) c. Remove jumper wires A through F from 14-pin IC
socket. (See component location drawing with sche-
e. Adjust test oscillator output level to 1.8 V. If matic diagram, Figure 7-2.) Place jumper in position
waveform at A7TP2 is a clipped wave approximately G.
4 V peak-to-peak, A7IC3 comparator is operating d. Connect ac calibrator to 3484A input and adjust
correctly with a constant input signal. If not, trouble-
shoot A7IC3 and its associated input circuit. output frequency to 100 kHz.
e. Follow the procedure in Figure 5-5, repeating until
f. If waveform in Step e is correct, set 3484A A7W8 can be adjusted properly (Step 3).
FUNCTION to VAC(DC), RANGE to 10 V.
f. Perform Adjustment Procedures outlined in Para-
g. Adjust test oscillator output level to 3 V. graph 5-7.
1. Set ac calibrator output to 10 V and
record 3480AlB display.
I
2. Reduce calibrator output to 1 V. Is
3480AlB display greater than 1/10
the reading recorded in Step I?
YeS No
I I
3. If display is less than 150 counts 4. If display is ,150 counts or more 5. Leave jumper in position and insert
greater, adjust A7R98 for display of above 1/10 of reading recorded in another jumper in next lower position
1/10 that recorded in Step 1. Step 1, remove last jumper installed (progressing from G to A). Return to
and insert in next lower position Step 1 and repeat.
(progressing from G to A). Return to
Step 1 and repeat.
Figure 5-5. 1/10 Scale Coarse Adjustment.
5-8 |
ACEC
