VERTICAL TROUBLESHOOTING HINTS
HORIZONTAL TROUBLESHOOTING HINTS
HOW TO VERIFY THE CONTROL DATA
AND CONTROL CLOCK LINES
With no signals connected to the four Vertical input connec-
tors,
select each channel for display and rotate its POSITION
con-
trol through its entire range.
If possible, set the instruments TRIGGER controls so the
TRIG'D LED remains illuminated (triggered sweep is running). Set-
ting the TRIGGER MODE to AUTO LVL will usually do this.
1.
Power up the instrument under test.
If one or more of the four Vertical channels properly
responds to its POSITION control, the problem is in the
preamp circuit of the defective channel or in the Vertical
Channel Switch circuit. If none of them respond prop-
erly, the Channel Switch, Delay Line, Vertical Output
Amplifier, and the Hybrid power supplies should
be suspect.
Check the range of the input positioning voltage for a
faulty channel. Channel 1 and 2 positioning inputs (pin
17 of U100 and U200) should vary between -4.6 volts
and -5.26 volts. Channel 3 and 4 positioning voltages
(to pins 29 and 32 of U300) should vary between
ground potential and -
5
volts.
If the faulty channel's input positioning range is okay,
check the positioning effect at the outputs of the Chan-
nel Switch (connect a DMM across the Delay Line).
When the CH 1 or CH 2 POSITION control is rotated
through its range, the DMM reading should vary from
approximately +700 mV to -700 mV; for Channels 3
and 4, it should vary approximately from +350 mV
to -350 mV.
4.
If the range at the Delay Line is okay, connect the
DMM across the vertical outputs to the CRT (between
L628 and L633). Range should vary approximately
from +11.5 volts to -11.5 volts as the POSITION
control of the displayed channel is rotated through its
range.
1.
Check that the horizontal positioning input (pin 22 of
U800) of Output IC varies approximately from -1.25
volts to +1.25 volts as the Horizontal POSITION
con-
trol is rotated through its range. If it does not, repair
the position circuit.
2.
Check that the A Sweep Ramp at pin 18 of U800 is
ramping from -1.25 volts to +1.25 volts. If it is not,
check the buffer amplifier made up of U735 and its
associated components. When operating properly, the
voltages and waveforms at pins 3 and 9 of U735 will
be nearly identical.
3. Check for proper select signals (TTL levels) at the HSA
and HSB inputs of U800.
4.
Check the power supply levels to U800.
5. Check the voltage on pin 6 of U800. If it is not > +80
volts,
check the +OUT and —OUT pins for shorts.
See the "Theory of Operation" for further information.
2.
Move the NORM/DIAG jumper (P503 on the
scope under test) to the DIAG position. This
forces the processor into a NOP loop and exer-
cises the Address Decode circuitry.
Trigger the test scope on the PORT 4 INH at pin
15 of U2550 (on the Control Board). Use NORM
TRIGGER and - SLOPE. Set TRIGGER LEVEL
to +1.4 volts.
4.
Verify that sixteen bursts of sixteen pulses each
occurring at 52 ms to 53 ms intervals.
5. Check that each of the outputs of U2550 has
similar signals present (diagram 2).
6. Check that each output of U2650 and U2660
(diagram 2) has sixteen bursts of one pulses
each occurring at 52 ms to 53 ms intervals.
7. Turn instrument power off and restore P503 to
the NORM position.
8. Power up the instrument again.
5. If the output voltages to the CRT are okay, check that
the voltage between the CRT termination resistors
(LR1513 and LR1514) varies approximately from
+ 11.5 volts to -11.5 volts as the POSITION control is
rotated through its range.
See the "Theory of Operation" for further information.
9. Set the instrument's CH 1 and CH 2 input
cou-
pling to 1 Mfi DC and TRIGGER MODE
to NORM.
10.
Hold in the upper TRIGGER COUPLING switch.
11.
Trigger the test oscilloscope on the DISP SEQ
CLK (pin 7 of U2650 or pin 10 of P512).
12.
With the test scope still triggered on the DISP
SEQ CLK, verify that the ATTN STRB at pin 2 of
P512 is eight positive-going strobes. Verify that
the control data on pin 1 of P512 is toggling at
TTL levels.
To Next Page
Loading...
