HP A Series User Manual

covered under the sympton "Oscillation" in Table 5-2.
Random frequency noise is most often caused by a
defective reference diode, VR2. A defective I.C.
(U1 or U2) can also cause this problem.
5-49 If a line frequency ripple problem exists, check
the ripple at the dc input to the reference supply across
test points B and N. It should be less than 600mV p-p.
If it is significantly greater than 600mV, check C1, CR1,
and CR2. If it is less than 600mV, check the ripple
between test point R and -i-S (+6.2V). The ripple at
T.P. R should be less than 1mV p-p. If it is greater
than 1mV, check VR2, Q1, and U1, in that order.
5'50 If the ripple is not excessive in the reference
supply, check the ripple across the main filter capac¬
itor (T.P. F to +S}. It should be less than 200mV p-p
at no load or less than 3V p-p at full load. If the ripple
here is significantly larger, check C9, CR3-CR6 (or U4),
and C4, in that order.
5-51 Spikes occurring at a 120Hz rate can be caused
by an open C4 (or C5) if included. Try repositioning
the leads in the rectifier area (CR3-CR6, or U4) if the
spike problem persists.
5-52 Crowbar Troubleshooting
(Units with Option 011 or 104 Only)
5-53 The following table provides continued trouble¬
shooting information for both option 011 and 104.
Operating instructions, circuit descriptions and
schematics for both crowbars are contained in the
applicable Appendix; A or B.
5-54 REPAIR AND REPLACEMENT
5-55 Cover Removal
5-56 A Suffix Supplies. To remove the wrap-around
cover on "A" series supplies, remove two screws each
from the front and rear of the package and lift cover
away from unit. If unit is equipped with an optional
crowbar, sufficient lead length is provided so that the
cover can be placed beside the unit,
5-57 C and E Suffix Supplies. To remove the covers
for both the "C" and "E" series supplies, proceed as
follows:
a. O n right side of package, remove two screws
approximately 5 inches to rear of the front edge of
package. This loosens top and bottom L-shaped covers.
b. To remove top-front cover remove four screws
on front of unit; one per corner.
c. To remove bottom-rear cover, remove four
screws at rear of unit; one per corner.
5-58 Main P.C. Board Removal
5-59 A Suffix Boards. To remove the main P.C. board
in "A" series supplies, proceed as follows:
a. Remove cover (previously describedK
b. Remove two screws about 1/2-inch from rear
edge holding terminal strip bracket.
c. Remove two screws about 3-inches from rear
edge holding P.C. board.
d. Push P.C. board toward bottom of unit until
top edge clears top slot in side cover.
e. Pull board from top slot then out of bottom
slot and rotate for access to circuit side.
f. Ensure that leads are not pinched when re¬
assembling.
5-60 C and E Suffix Boards. To remove P.C. board for
these supplies, proceed as follows:
a. Loosen right cover and remove top-front cover
(previously described).
b. Remove bottom-rear cover.
c. Remove left side cover by removing two screws
about 5 inches back from front edge and two screws
holding terminal strip bracket.
d. Board and series regulating transistor{s) are
now exposed for servicing or removal.
5-61 Series Regulator Replacement
5-62 To remove and replace a series regulating tran¬
sistor, proceed as follows:
a. Remove covers (previously described),
b. Remove collector screws and unsolder base
and emitter leads.
c. To replace transistor, follow the below re¬
assembly order, as viewed from bottom of heat sink:
Collector screw, flat washer, shoulder washer, heat
sink, silicon grease (Dow DC-3, HP 6040-0209, or
HP 8500-0059), mica insulator, more silicon grease,
transistor, electrical lug (on one collector screw), lock-
washer and nut. (On "A" series transistors, the base
and emitter pins have associated insultor bushings.)
5-63 Capacitor Replacement (A Suffix Supplies)
5-64 Due to space limitations in "A" series supplies,
some of the filter and output capacitors (C9 and Cl 1)
5-11

HP A Series Specifications

General

Brand	HP
Model	A Series
Category	Power Supply
Language	English