Sect.IV Page 2 Model 405C
B. EXTERNAL TRIGGER CHECK 4-5 POWER SUPPLIES
1) Set SAMPLING control to EXT. Check power supply voltages and regulation as part
of routine maintenance and as a first trouble-
2) Connect trigger generator to EXT TRIG con- shooting step. If the voltages are essentially cor-
nector on rear of 405C. rect and properly regulated (the +300 and +120
supplies are not regulated), the supplies are oper-
3) Adjust trigger generator output for positive ating properly.
pulse (square wave will do) 20volts peak. Set trig-
ger repetition rate to 5 per second and observe You can check regulation of the power supplies by
405C readout. If it is not apparent that 405C
is sampling five times per second, vary voltage monitoring their voltages while varying line voltage
between 103 and 127 volts. The regulated voltages
applied to INPUT connector and watch rateat which should vary only slightly, if at all, from the value
readout changes.
measured at a 115-volt line. Figure 4-5 shows
convenient points to measure the voltages.
C. CALIBRATION STANDARD CHECK
(Instrument must have 15 minutes warm up The 250-volt supply is the only adjustable supply,
before you make this check.) and it should seldom require resetting. If you do
adjust it, use a voltmeter accurate within 3% of
1) Set SAMPLING control to maximum (clockwise) full scale and following the adjustment checkampli-
but not to EXT, and set RANGE switch to AUTO. fier balance (paragraph 4-6) and neutralization
(paragraph 4-7).
2) Connect calibration generator to 405C INPUT
connector and adjust generator output to + 0.8 volt.
3) Adjust 405C CALIBRATE control to produce
readout of +.800. 4-6 BALANCING THE AMPLlFlER
4) Press CALIBRATE switch; readout should 1) Remove top dust cover.
agree with voltage stamped on tag under CALI-
BRATE engraving on front panel. 2) Set line voltage to 115 volts, turn instrument
on and allow 5-minutes warm up.
D. MANUAL RANGING CHECK
1) Set RANGE switch to HOLD. Range should re- 3) Set RANGE switch to AUTO and SAMPLING
control to maximum (clockwise) but not to EXT.
main constant regardless of voltage applied.
2) Set RANGE switch to STEP and release. In-
4) Connect calibration generator to 405C INPUT
strument should step to next more positive range connector and set generator output to+0.8 volt (any
except that three blank positions occur between
convenient voltage will do provided you can change
+9.99 and +99.9 volt ranges. The decimal point its polarity without changing its amplitude).
is not lighted on the blank ranges.
5) Adjust CALIBRATE control until voltmeter
4-4 CABINET REMOVAL
reads +.800.
The 405C has top and bottom dust covers. Each
cover is held by two screws in the rear. When
6) Change calibration generator output to -0.8 volt.
sliding either cover off, you may have to lift the
front edge of the cover to clear internal components.
7) Adjust Coarse Bal R14 until 405C reads -.800.
NOTE
Turn the 405C off before removing or replacing
the dust covers. 8) Repeat steps 4 through 7 until 405Creads +.800
----------------- and -.800 without adjustment.
00518-1 |
ACEC
