HP A Series User Manual

are secured with nylon cable ties. These ties must be
cut to remove C9 or C11. Replacement capacitors in¬
clude these ties when ordered from Hewlett-Packard.
Cable ties can also be ordered separately. Both C9 and
C11 require Panduit type SST-2, or HP 1400-0265,
cable ties. The ties can be installed with a special
tool, such as a Panduit GS-2B, or with a pair of long
nose pliers.
5-65 To replace the capacitor, proceed as follows:
a. Thread pointed end of tie through holes in
P.C. board from top. Ensure that gripping teeth are on
inside of loop being formed.
b. Insert capacitor in proper position on board.
Head of cable tie should face inside of unit.
c. Tighten cable tie with tool or pliers. Cut ex¬
cess about 1/4-inch from head.
d. Soider and trim capacitor leads.
5-66 Crowbar Board Removal
5-67 A Suffix Supplies. To remove the crowbar board
(optional) on "A" series supplies, first remove the
cover. Next, remove one number six and one number
eight screw holding the crowbar board, if the SCR is
replaced, use the same silicon grease recommended for
the series regulating transistor.
5-68 C and E Suffix Supplies. For "C” and "E" series
supplies, the crowbar board is removed as follows:
a. Loosen right side cover.
b. Remove top-front cover.
c. Remove one seif-tapping screw from center
of bottom-rear cover.
d. Loosen other seif-tapping screw and rotate
board upward to gain access to components.
e. To remove board, remove second self-tapping
screw completely.
f. If SCR is replaced, use silicon grease recom¬
mended previously for series regulator.
5-69 Semiconductor Replacement
5-70 Table 5-7 contains replacement data for the semi¬
conductors used in the modular supplies described by
this manual. When replacing a semiconductor, use a
Hewlett-Packard part or an exact commercial replace¬
ment part, if applicable. In cases where neither of
these parts are immediately available and a part is
needed for emergency operation or troubleshooting
verification, the first or second alternate part (see
Table 5-7) can be tried with at least a 90% probability
of success. Also, the user has the option of hand select¬
ing the alternate part by using the device characteristics
listed in Table 5-7.
5-71 Notice that these alternate replacements apply
only to the HP modular power supplies and their use
in any other Hewlett-Packard instrument is not
authorized because of inclusion in this table.
5-72 Current Limit Adjustment
5-73 The current limiting point for the supply is fac¬
tory set to 104 ± 1% of the current rating with the out¬
put voltage set at nominal. As described in Paragraph
3-8, the current limit may require readjustment at out¬
put voltages other than nominal. The current limit
should also be checked and adjusted, if necessary,
after replacement of R15, R17 (if used), R18, or
R19. Proceed as follows to check and adjust the cur¬
rent limit:
a. Connect setup shown in Figure 5-6,
b. With Rl at maximum, set output voltage to
desired value.
c. Decrease R[_ until current limit is reached
(substantial increase in 120Hz ripple observed on
scope). Reading on voltmeter is equivalent to current
limit point.
d. If current limit of Step c is not 104 ± 1% of
maximum current rating, change current limit by
first increasing Ri_.
e. Next, use insulated tool to increase current
limit setting (turn R18 clockwise).
f. Again decrease Ri_ until voltmeter reads
value equivalent to 104 ±1% of maximum output
current.
g. Decrease current limit setting (R18 ccw) until
supply current limits (ripple increases on scope).
Figure 5-6. Current Limit Adjustment Setup
5-12

HP A Series Specifications

General

Brand	HP
Model	A Series
Category	Power Supply
Language	English