HP 3000 III Series Manual page 341

HP 3242lA Series III Power Supplies
screws, or other metal objects onto con-
ductors. Remove power and recover dropped
objects at once; if forgotten, damage
could result later.
Ac
power line vol tage and 130 vol ts dc are
exposed when covers are removed. Exercise
extreme caution when working in the power
supply with covers removed, and never work
under this condition unless another person
is nearby and within sight. Also, remem-
ber that the test equipment is floating
with respect to earth ground, so the cases
can be at the same line voltage a~ the
point being measured in the power supply.
Thus, test equipment must be temporarily
enclosed and marked dangerous to alert all
personnel of unsa fe condi tions.
If feasible, be fore per form ing any wor k
inside the power supply, unplug the ac
power cable and wait three minutes for
f il te r capacitor s to discharge. To p re-
vent explosion resulting from internal
heating, always be sure to replace filter
capacitors properly with respect to
polarity.
The highest ac voltage in the power supply is the ac line voltage
(250 volts rms, 350 volts peak). The highest dc voltage in the
power supply is 130 volts. The ac line voltage is exposed at the
input circuits of the power supply and at filter choke Ll. The
130 volts dc is exposed at the preregulator filter circuit and
the inverter assembly A7. Additionally, ac voltages of 240 -volts
peak are exposed at transformers Tl and T2.
If the test equipment has a metal case, the negative test lead
should not be connected to the case. Also, the negative lead
should not be connected to digital voltmeters that have floating
(guarded) inputs, to mul timeters, nor to power supply chassis.
Instead, the test equipment chassis should be connected to the
computer system cabinet earth ground through the test equipment
power cable. Consequently, the oscilloscope case will "float"
with respect to earth ground. All test equipment should be plug-
ged into the ac power convenience outlets provided in the comput-
er system bay
cabinets~
All measurements and connections to the power supply must be ref-
erenced to the appropriate common circuit. There are four such
circuits within the HP 303l0A Power Supply:
common~, comrnon~,
commonW" and common
W.
In subsequent paragraphs, all test and
adjustment procedures specify the particular common circuit to be
used.
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