HP A Series - Page 25

Table 5-3. Low Output Voltage Troubleshooting (Continued)
STEP
ACTION
RESPONSE
PROBABLE CAUSE
7
NOTE: Q3 not included on
Check conduction of
drive Q3 by shorting
collector of Q2 (T.P. D)
to terminal
62048A. To check serie
a. Output voltage
increases.
b. Output voltage
remains low.
s regulator, perform action of Step 7.
a. Proceed to Step 8.
b. Driver transistor Q3 open.
8
Check conduction of
Q2 by shorting T.P. D
to +S.
a. Output voltage
increases
b. Output voltage
remains low.
a. Proceed to Step 9.
b. DriverQ2 open.
9
Check turn-up capa¬
bility of U2 by shorting
pin 2 of U2 to +S.
a. Output voltage
increases
b. Output voltage
remains low.
a. U2 is good. Check for defective
input circuit component; R5, R7,
R8, R11,CR11,orCR12.
b. Check for open CR13, or de¬
fective feedback capacitor Cl 3 or
C14. If these components are good,
replace defective U2.
Table 5-4. High Output Voltage Troubleshooting
STEP
ACTION
RESPONSE
PROBABLE CAUSE
1
Check turn-off of series
regulator by shorting
base-to-emitter of Q4
(shortcut R30).
a. Output voltage
decreases.
b. Output voltage
remains high.
a. Proceed to Step 2.
b. Series regulator transistor(s) Q4
(05) shorted. Protection diode (CR8
or U5) shorted.
2
Check turn-off of dri¬
vers Q2 and Q3 by
shorting base of Q2
(T.P.G) to +S.
a. Output voltage
decreases
b. Output voltage
remains high.
a. Proceed'to Step 3.
b. Driver transistor Q2 or Q3 shorted.
C18 or C19 shorted.
3
Check turn-off capa¬
bility of U2 by short¬
ing summing point (at
pad W1) of U2 to -
output terminal.
a. Output voltage
decreases
b. Output voltage
remains high
a. U2 is good. Check for defective
input circuit component; R5, R7, or
R8.
b. Check VR1 for—7.5V bias. If OK,
check for open CR13 or shorted Cl3,
Cl 4, C R11 or C R12. If these compo¬
nents are good, replace defective U2.
5-9