45
If the unit has failed selftest by reporting an error 105-108 at turn-on and no problem can be found using S.A., the IMON
adjustment may be at fault. Refer to ''POST REPAIR CALIBRATION" and perform the IMON Adjustment.
Also, check if the switches in U309 are operating properly. Turn off the S.A. mode by removing the jumpers. Now check
test points
,
and
using the measurement conditions specified in Table 3-3. A switch should close when the
applicable test point is a Low level. If the switches are operating properly, check test points
( - IMON),
(-10V),
and
( - VMON)
If all signatures and test points check out, the DAC or amplifier that is generating the incorrect waveform is probably faulty.
Slew Circuit Troubleshooting (Figure 3-4)
This circuit consists primarily of three operational amplifier stages (U306 and U307) and four analog switches (U317). The
four switches determine the slew rate by selecting loop gain and response time combinations. The switches are controlled
by the SLW1-SLW4 signals to provide 12 slew rates.
To troubleshoot the slew circuit, place the Electronic Load in the S.A. mode by connecting the jumpers in test headers
TP201 and TP301 in the S.A. mode positions (see Figure 3-2). The S.A. waveforms at the top of Figure 3-4 can only be
generated when the S.A. mode is on. If the S.A. waveforms are incorrect, check the SDB0-7 data inputs to U305 and the
SLW signal outputs from U305 using S.A. Table 3-13. If the signatures are correct, an amplifier or switch is probably
defective.
The waveforms at the bottom of Figure 3-4 are generated when various slew rates are programmed. These waveforms
check the operation of the slew circuit switches (U317). They are not generated in the S.A. mode. To generate these
waveforms, turn the S.A. mode off (remove jumpers) and program 3 different slew rates ( .001, 0.5 and 2.5 A/
µs) from the
front panel as shown in the following sequence. Use a scope with delayed sweep to verify the waveforms shown for slew
rate in Figure 3-4.
MODE = CURR
CURR = 5
Tran Level = 10
Freq = 80
Dcycle = 50
Tran on/off = on
Slew = .001 (Slew Rate #1)
Slew = .5 (Slew Rate #9)
Slew = 2.5 (Slew Rate #11)
}
6060B
only
The three slew rates programmed from the front panel toggle all four switches in the slew circuit. Refer to the following
table if you need to check the state of the switches for a specific slew rate. Remember that the front panel is programmed in
microseconds. Note that when the SLW signal is LO, the switch is closed; when the SLW signal is HI, the switch is open.
If the slew rate tests check out, and a problem still exists, troubleshoot the CC/CV control circuits as described in the next
section.
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