Telequipment DM64, Manual

Page: 18 / 63

4.1.1 The entire solid-state design of the instrument should
render frequent re-adjustment of the internal preset controls
unnecessary; however, to ensure full measurement accuracy,
it is desirable to make an occasional check, reference 4.3.2,
4.3.3. on the vertical amplifier sensitivity and timebase sweep
speed. The internally generated 500 mV peak to peak calibra-
tion waveform may conveniently be used for these checks.
4.1.2 Should a more complete calibration be required, such as in
the event of transistor replacement, reference should be made
to the appropriate procedure in the Calibration paragraph of
this Chapter.
Before it is assumed that a fault condition exists, control
settings should be verified with reference to the Pre-Operation-
al checks,paragraph 2.2.
Attenuator trimmers are accessible from the left hand side,
front, after the covers havebeen removed. PC.110 and PC.111
which carry the circuits for the timebase, power supplies and
storage are situated on the right hand side; PC.115, the
vertical amplifier
is on the left hand side and PC.123, the
E.H.T. is below the rear of the CRT. The boards are marked
with a legend to facilitate component identification.
The cabinet sides are removed as follows:
1. Disconnect the power supply.
2. Loosen the two handle-clamp securing ~cre.·'s.
3. Easethe top of each .:::ie outwarrls.
4. Unhook the bottom
of e?'"h siti.: fro
1""1
the locating
slots. The chassis base cover plate is secured by six
fixing screws, one at each corner and one half-way
along each side.
1. Remove both cabinet sides, as described above.
2. Remove the rear cover (four screws).
3. Unplug the 14 pin CRT baseconnector.
4. Unplug the five pin connectors (top, rear PC.111).
5. Remove the three screws holding the mumetal screen.
6. Unplug the trace rotation coil connector (rear PC.115L
7. Remove the CRT and screen from the instrument by
moving them towards the rear to clear the front panel;
moving the forward end of the CRT to the left. The
CRT and screen may be removed with the cableform
attached.
8. Remove adhesivetape and rear location moulding from
the CRT.
9. Remove the CRT from the screen.
4.2.4 CRT FITTING
Reversethe order detailed above 4.2.3. Ensure that the CRT
forward end is located in the rubber moulding behind the
front panel. If the trace rotation control does not provide an
adequate range of adjustment reversethe trace rotation plug.
4.3.1 The following procedure enables a full calibration of the
instrument to be accomplished. If any operations are carried
out in isolation, regard should be paid to the risk of inter-
action with
other adjustments also to control settings and
waveforms applied in earlier steps.
The following tools and equipment shall be required:
1. Calibrator, Telequipment Type C1A or Item 2.
2. Time Marker Generator and an accurate voltage source.
3. Signal Generator.
4. Terminator,
50~. If alternative to 1 above is used, a
suitable matching terminator should be used.
5. Variac with a
±
10% facility.
6. Avometer.
7. Oscilloscope with 100 mV/Div sensitivity.
8. Voltmeter with range ;;"3.5 kV.
9. X1 Probe.
10. X10 Probe.
11. Non capacitive trimming tool.
12. Screwdrivers with various width blades.
4.3.2 SWEEP SPEED CHECK
1. Switch CH1 and CH2 on.
2. Set VOL TS/DIV to 100 mV.
3. Turn VARIABLE
fully clockwise and releasefor
XL
4. Set DC·GND-AC to DC.
5. PushFINEforX1.
6. Set TIME/DIV
to 10 ms.
7. Turn VARIABLE (speed) fully clockwise.
8. Connect INPUT 1 & 2 to CAL.
9. Adjust STABILITY
for locked display.
10. Check Sweep Speed = 1 cycle/2 divs. for 50 Hz supply
3 cycles/5 divs. for 60 Hz supply
for 400 Hz supply set TIME/DIV to 1 ms
check Sweep Speed
=
2 cycles/5 divs.
4.3.3 GAIN CHECK
1. Repeat 1 through 5 above.
2. Connect CAL to INPUT 1.
3. Adjust CH 1 POSITION, Trigger and Sweep controls for
convenient display.
4. Check amplitude
=
5 divs. if incorrect adjust R617.
5. Connect CAL to INPUT 2.
6. Adjust CH2 POSITION,
Trigger and Sweep controls
for convenient display.
7. Check amplitude = 5 divs., if incorrect adjust R691.
NOTE: VARIABLES must remain fully clockwise.