Feedback Loop Isolation - HP 6269B Operator’s, Organizational, Direct Support And General Support Maintenance Manua L

TM 11-6625-2958-14&P
5-7, the circuit is checked by starting with the
output waveform and tracing backwards.
5-61 Performing the tests given in Table 5-5, 5-6,
and 5-7 will usually require partial disassembly of
STEP ACTION
NOTE: After each step, crowbar should be reset by turning supply off and then on.
1 Inspect LINE circuit breaker.
2 Inspect overvoltage lamp on
front pane 1.
3 Isolate fault to either series
regulator or preregulator by
using the following steps:
(1) Open the gate lead to
triac A2CR1 by disconnect-
ing either end of resistor
R88 (TP87 or TP88).
(2) Place a small dc pow-
er supply across the input
capacitors (C 101 through
C104). A 0-10V, 2A sup
ply is sufficient.
(3) Set external supply to
ten volts.
(4) Vary front panel volt-
age controls.
the supply in order to gain access to components
(such as the series regulator transistors) that are
not mounted on the main circuit board. If this is
the case, refer as necessary to Paragraphs 5-65
through 5-70 for disassembly procedures.

Feedback Loop Isolation

Table 5-4.
RESPONSE
a. Tripped.
b. Not tripped;
High voltage output.
c. Not tripped;
Low voltage output.
a.
On.
b. Off;
High voltage output.
c.
off;
Low voltage output.
a. Output voltage normal.
Variable from O volts
to about 9 volts.
b. Output voltage high.
Varying controls has
little or no effect.
-
c. Output voltage low,
Varying controls has
little or no effect.
5-12
PROBABLE CAUSE
a. Check rectifier, filter, and
triac for short. Faulty pre-
regulator. Procceed to Step
3.
b. Series regulator loop in
high voltage condition.
Proceed to Step 2.
c. Proceed to Step 2.
a. Check setting of overvolt-
age adjust (A5R125).
Check A4CR110 for short.
Series regulator loop in
high voltage condition.
Proceed to Step 3.
b. Check setting of overvolt-
age adjust (A5R125).
Check A4CR110 for open,
Q91 for open, Q92 for
Series regulator
short.
loop in high voltage con-
dition. Proceed to Step 3.
c.
Check overvoltage adjust
(A5R125). Check A4CR110
for short. Check Q20 for
for short. Proceed to Step
3.
a. Check each series regula-
tor transistor (A4Q103
through A4Q108) for open.
Then check preregulator
by disconnecting source
and proceeding to Table
5-7.
b. High voltage condition in
series regulator.
to Table 5-5. Leave ex-
ternal source connected.
c. Low voltage condition in
series regulator loop.
Proceed to Table 5-6.
Leave external source
connected.
Proceed