HP Lab Series - Page 42

Table
5-3.
O~·erall
Troubleshooting
SYMPTOM
CHECKS
AND
PROBABLE
CAUSES
•
High
Output
Voltage
a.
Check
series
regulator
·feedback
loop
or
prer.-egulator
feed-
back
loop.
Refer
to
Paragraph
5-62
and
then
Table
5-4
or
5-6
as
instructed.
Low
or
No
Output
Voltage
a.
If
output
is
zero,
check
fuse.
b.
Check
series
regulator
feedback
or
preregulator
feedback
loop.
Refer
to
Paragraph
5-62
and
then
Table
5-5
or
5-6
as
instructed.
High Ripple
a.
Check
operating
setup
for
ground
loops.
b.
If
output
floating,
connect
Iµf
capacitor
between
output
and
ground.
c.
Ensure
that
supply
is
not
crossing
over
to
constant
cur-
rent
mode
under
loaded
conditions.
d.
Check
for
low
voltage
across
Cl4
or
Q6.
e.
Check
for
excessive
ripple
on
reference
voltages.
(Table
5-2)
Poor
Line
Regulation
a.
Check
reference
circuit.
(Paragraph
5-59).
b.
Supply
current
limiting.
c.
Check
reference
circuit
adjustment
(Paragraph
5-8
3).
Poor
Load
Regulation
a.
Measurement
technique
(Paragraph
5-11).
••
(Constant Voltage)
b
•
Check
reference
circuit
(Paragraph
5~59,
VRl).
c.
Ensure
that
supply
is
not
going
into
current
limit.
Check
constant
current
input
circuit.
Poor
Load
Regulation
a.
Check
reference
circuit
(Paragraph
5-59,
VR2)
and
adjust-
(Constant Current}
ment (Paragraph
S-83).
b.
Cl9,
C20,
and
CR34
leaky.
c.
Check
clamp
circuit
QlO,
CR30,
VRS,
and
CR32.
d.
Ensure
that
supply
is
not
crossing
over
to
constant
volt-
age
operation.
Check
constant
voltage
comparator
circuit.
Oscillates
a.
Check
CS
for
open,
adjustment
of
R30 (Paragraph
5-86}.
(Constant
Voltage
I
Constant
Current)
b.
Check
R20, C3
in
constant
current
comparator
circuit.
c.
Check
CR19
and
C26
in
SCR control
circuit.
Poor
Stability
a.
Check=
6.2Vdc
reference
voltages
(Paragraph
5-60).
(VRI
(Constant
Voltage)
and
VR2.)
b.
Noisy
programming
resistor
RIO.
c.
CRl,
CR2
leaky.
d.
Check
Rl,
Rl2, Rl3,
C2
for
noise
or
drift.
e.
Stage
Ql
defective.
Poor
Stability
a.
Check
:6.2Vdc
reference
voltages
(Paragraph
5-60).
(VRl
(Constant
Current)
and
VR2.)
•
5-11