Fluke PM6690, Service Manual, Page: 78 / 200

On connection of line power, R478 and C389 keep the
RESETN input of the flip-flop U29 low. This sets the QN out-
put of U29 high. Via Q47 (output signal low) and Q58 (output
signal high) the secondary power supply will be set in ON
mode. To switch to the standby mode, the processor sets the
SETN input of U29 low. This results in the QN output being
low and the secondary power supply being set to standby
mode via Q47 (output signal high) and Q58 (output signal
low). In standby mode a bleeder circuit on +5 VU is
connected. It draws approximately 100 mA to stabilize the
AC/DC module. The standby LED on the front panel is
switched on. To switch to ON mode from standby mode, a
negative pulse, generated by pressing the ON/OFF key on the
front panel, is connected to the RESETN input of U29.
Linear regulators are used for some voltages to ensure mini-
mum noise. Check the TPs below:
X12: +3.3 VA (from +5 VU)
X8: -5.2 VA (from -15 VU)
X10: -12 VA (from -15 VU)
X62: -5.2 VI (from -12 VA)
X25: -2.1 V (from -12 VA)
X16: +12 VA (from +15 VD)
X17: +12 VU (from +15 VU) (to oven oscillator, not
switched off in standby mode)
For digital and general use some voltages are generated by
DC/DC converters. Check the following TPs:
X14: +3.3 VD (from +5 VU)
X2: +1.8 V (from +5 VU)
Some voltages derived directly from the AC/DC module are
used as secondary supply voltages without further regulation,
and they have semiconductor switches in series to make it
possible to shut them off in standby mode. Check the TPs be-
low:
X15: +15 VD (from +15 VU)
X11: +5 VD (from +5 VU)
X13: +5 VA (from +5 VD)
These 12 secondary voltages are used all over the instrument.
All secondary supply voltage lines are segmented into
branches with ferrite beads. See the schematics. This makes it
easier to isolate short circuits by removing ferrite beads tem-
porarily.
The microprocessor, U13, has an internal linear regulator that
gen1.8 V from +3.3 V. This voltage is used by the pro-
cessor core and can be checked at X66.
6-34 Troubleshooting
Figure 6-56
PCB1 survey
See Fig. 6-57 See Fig. 6-58