HP 182C - Page 94

Table 8-8.
CRT Intensity
Troubleshooting
Tips
1
Symptom
!
Suggested
Checks
Low intensity
*Most
common fault.
Check Intensity
Limit Adj.
Check low voltage supplies.
Check High Voltage Supply.
Check Gate Amplifier and gate connection
to
H.V.
Oscillator
& Rectifier assembly.
•Check CRT.
(See Notes
for
additional tips.)
High intensity
Make checks listed for low intensity.
'Check
H.V. power supply diodes.
Check CRT for grid-cathode
leakage.
Check CRT for open grid
circuit.
(See Notes for additional tips.)
Flickering intensity
Check High Voltage supply for arcing.
Check High Voltage leads for arcing.
Check CRT for loose connections
to pins.
Check CRT for possible intermittent
internal
connection.
Check High Voltage regulator for
intermittent
components or
connections.
Check High Voltage
Supply
for
intermittent
components
or connections.
Check oscillator
connections.
(See Notes for additional tips.)
NOTE 1
When troubleshooting
the High Voltage Power
Supply or CRT it is helpful
to isolate the
CRT.
Do this
by
disconnecting
CRT base socket and
Post Accelerator High
Voltage connection.
With CRT disconnected, the
High Voltage circuit is not loaded
by the CRT if
it is at
fault,
and
the CRT is protected if the
High Voltage supply is faulty.
NOTE
2
The
CRT may be checked
to determine if grid-cathode
voltage is correct.
Use a high-impedance
voltmeter
(VTVM) which has isolated
input terminals to measure grid-cathode
voltage.
(Voltmeter input terminals must
be isolated from ground,
i.e.: floating, since
grid and cathode
are at high voltage in relation to ground.)
With INTENSITY
control set for maximum intensity
(fully
cw). grid should be more negative
than cathode by about 20V. With
control set for
minimum intensity (fully
CCW) grid
should be more negative
than cathode by about 60V.
NOTE 3
In checking for cause of excessive
high voltage, remember
that increased resistance
in the
feedback regulator
loop will result
in
increasing
the H. V. oscillator output.
High Voltage
output from the
supply will
therefore
be increased. Conversely,
low
output
from
the High
Voltage supply will result
if the feedback loop resistance
is lower than normal.
Low voltage
can also be the result of
Increased loading.