Heathkit ID 4850 Operation Service Manual

Page 1

OPERATION /$ERVICE
MANUAL

HEATH-
| 11-w-

Page 7

Some of the outetandlnggfeetures when you use the
DMO with a computer tn¢lude=

0 Control over longldistences via RS.232.

0 Control via a modem.
0 Signal averaging.
Inversion of eithei' channel.

Hard copy outputbf the screen display.

Cursor measurement of voltage and differen-
tial voltage.

Cursor measurement of frequency, time. and
time difference.

0 Waveform storage on disk.

This DMO is a lsboretorymde ten instrument that
is ideal for a wide range of measurements used in
electronic development, education, production
lines. and scientific research.

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12.

13.

14.

15.

TIME BASE RATE '- Push this pushbutton
to decrease the time base rate. The LEDs to
the left of this pushbutton (9) show the time
base that has been selected. The display out-
put is calibrated in; TIME/DIV for a display
oscilloscope that has a graticule which con-
tains ro horizontalvdivisions. When a time
base between 500 rue/DIV and 20 leIV is
selected. the trigger channel is shown on the
display oscilloscope as it is being sampled
[trigger view). NOTE: If the NOW-
BRATE jumper on the main circuit board is
at NORMAL. the DMO will automatically re-
zero the vertical amplifiers when you change
the time base rate.

This indicator (not labeled) lights when you
press the SAVE pushbutton to indicate that
a waveform has been stored in auxiliary mem-
ory.

SAVE - If the LED to the left of this pushbut-
ton is off, push this pushbutton to save the
waveforms that are currently being displayed
in auxiliary memory. The LED lights and the
saved" waveforms are displayed continu-
ously. All functions of the input channels re
main active. This feature allows you to com-
pare live waveforms with the "saved"
waveforms. If you push this pushbutton while
the LED is lit. the auxiliary memory is erased
and the LED is turned off.

+ 0 - indicators - These indicators show
you whether the trigger level is above ground
(+ ), at ground (0). orbelow ground (- ).

TRIGGER LEVEL :- Push this pushbutton
to increase the trigger level. Simultaneously
press both the A and V pushbuttons to set
the trigger level to ground [0 indicator will
light). This allows you to quickly return the
trigger level to ground. NOTE: If the NOR-
MAL/CALIBRATE jumper on the main circuit
board is at NORMAL, the DMD will automati-
cally more the vertical amplifiers when you
change the trigger level.

16.

17.

18.

Whenever you push this pushbutton. the
channel selected as the trigger source and a
line that represents the trigger level are shown
on the display oscilloscope. If you have used
the position controls to raise or lower the
channel you selected as the trigger source. the
line that represents the trigger level will be
raised or lowered by the same amount. This
allows you to easily set the trigger level so
that the DMO triggers on a specific portion
ofthe waveform.

TRIGGER LEVEL V -- Push this pushbutton
to decrease the trigger level. Simultaneously
press both the A and V pushbuttons to set
the trigger level to ground (0 indicator will
light). This allows you to quickly return the
trigger level to ground. NOTE: If the NOR-
MAUCAUBRATE jumper on the main circuit
board is at NORMAL, the DMO will automati-
cally rezero the vertical amplifiers when you
change the trigger level.

Whenever you push this pushhutton. the
channel selected as the trigger source and a
line that represents the trigger level are shown
on the display oscilloscope. If you have used
the position controls to raise or lower the
channel you selected as the trigger source, the
line that represents the trigger level will be
raised or lowered by the same amount. This
allows you to easily set the trigger level so
that the DMO triggers on a specific portion
of the waveform.

AUTO-NORM-SINGLE indicators. These in-
dicators show you which nigger mode has
been selected.

TRIGGER MODE - Push this pushhutton to
select the trigger mode you desire (auto. nor-
mal, or Single Sweep). The LEDs to the left
of this puahbutton (17) indicate which trigger
mode has been selected. NOTE: If the NOR-
MAL/CALIBRATE jumper on the main circuit
board is at NORMAL. the DMO will automati-
cally rezero the vertical amplifiers when you
change the trigger mode.

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EXAMPLE 5 - VOLTAGE MEASUREMENTS

Peak-to-Peak Voltage Measurement:

To measure the peak-to-peak voltage of a signal,
count the number of divisions from the top of the
waveform to the bottom of the waveform. Then mul-
tiply the number of divisions by the VOLTS/DIV set-
ting of the appropriate channeL (It may be easier
to count the number of divisions if you first use the
vertical position controls to place either the top or
the bottom of the waveform on one of the graticule
lines.)

The waveform in Pictorial 1-20 should closely re-
semble the waveform on your display. The
waveform in the Pictorial is four divisions from peak
to peak. Assuming that the Y1 vertical channel sen-
sitivity is set to 100 mV/div, the peak-to-peak
amplitude of the signal is:

4 divisions x 100 mV/div = 400 mV

You could also use the cursors to make this measure-
ment. Example 8 shows you'how to use the cursors.

Ground-Referenced Voltage Measurements

To make a ground-referenced voltage measurement,
first make sure you use the vertical position controls
to center the channel you are using. When you have
the channel centered, the mound reference is the
center of the display. Count; the number of divisions
from the center of the displhy to the point you wish
to measure. As before, multiply this number by the
VOLTS/DIV setting of the channel you are using.

Again look at Pictorial 1-20 and note that the peak
of waveform 2 is two divisions above the center of
the graticule. The voltage at this point, therefore, is
(assuming the vertical sensitivity is still 100 mV/
div):

2 divisions x 100 mV/div = 200 mV

You could also use the cursors to make this measure-
ment as described in Example 8.

EXAMPLE 6 - TIME DURATION AND
FREQUENCY MEASUREMENTS

NOTE: If you are using your DMO with a display
oscilloscope, the front panel time base ranges as-
sume that the display oscilloscope has to horizontal
divisions. If your display oscilloscope has a different
number of horizontal divisions, you will have to
read your display as if it had 10 divisions to make
accurate measurements.

To find the time duration between two points on
a waveform, multiply the horizontal distance be.
tween the two points (in divisions) by the setting
of the TWASE. Frequency is the reciprocal of the
time duration of one cycle of a waveform.

increase the 'l'lMEBASE until two cycles of the sine
wave are displayed. [If you are using a 1000 Hz
sinewave. the TIMEBASE setting should be 200 as!
div.) Your display should be similar to the one
shown in Pictorial 1-21.

In Pictorial 1-22. one cycle of the sine wave is 5
divisions. One cycle, or the period. of the sine wave
is therefore:
5 divisions x 200 uddiv = 1000 res = 1 ms
The frequency is the reciprocal of the period or:
1 + 1 ms = 1000Hz

Return the 'l'lMEBASE to 500 its/div.

EXAMPLE V-MSETMMEASUREMENTS

NOTE: Refer to Pictorial 1-22 as you study this ex-
ample. Do not change any of the DMO's controls
yet.

Rise time measurements are a form of the time dura-
tion measurement. These measurements are made
between the 10% and 90% points on the edge of
a square wave transition. Use the following proce-
dare:

1. Adjust the controls of the DMO so that the
edge you want to measure fills as much of

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OSCILLOSCOPE SETUP

( ) Connect a suitable cable from the VERTICAL
OUTPUT of the DMO to the vertical input of
an oscilloscope.

( ) Connect the TRIGGER OUTPUT of the DMO
to the external trigger input of the oscillo-

scope.
( ) Preset the controls of the oscilloscope (not the
DMD) as follows:
Vertical Input Coupling DC
Vertical Position Center
Vertical Input Sensitivity .5 Voltsldiv
Sweep Speed 1 ms/div
Trigger Source Ext
Trigger Slope +
Trigger Mode Auto
Trigger Level Center

NOTE: If you obtain the horizontal traces but no
message. in the next step. change the TRIGGER
LEVEL control on the DME) either direction [+ or
-) until you have both the message and the trace.
If the message is off the top of the screen, adjust
OUTPUT CAL control R506 (on the display logic
circuit board) until it is onscreen. If you are using
a display oscilloscope that does not have eight verti-
cal divisions. adjust its Vertical Position until the
message is near the top of the screen.

( ) You should now see a display similar to the
one shown in Pictorial 2-4. Change the Trigger
Mode on the oscilloscope to Norm [no automa-
tic baseline) and adjust the Trigger Level for
a stable display. The trace should blank out
momentarily approximately once each second.
The exact position vertically oi the two hori-
zontal lines and the no trigger" message is
not important at this time.

( ) Adjust RT Zero controls R169 [for Y1) and
R269(for Y2) on the DMO main circuit board
until the traces are near the center of the
screen.

( ) Push the SAVE pushbutton on the front of the
DMD. The indicator just to the left of this
pushbutton should light.

( ) Separately push the Y1 and Y2 POSITION
pushbuttons to move the traces. There should
now be four traces.

NOTE: In the next step you will adjust the holdoff
for the shortest amount that will still display the
message and four horizontal traces.

( ) Refer to Pictorial 2-5 and, starting from the 10
ms setting (both W404 and IP405 at 1), move
the jumpers to the 7.5 ms setting. followed by
the 5 ms setting, and finally the 2.5 ms setting.
Madjust the Trigger Level control on your os-
ciiloscope after you make each change and
check for the proper display. Leave the jum-
pers in the fastest (shortest time) position that
will still display the "No Trigger" message and
four horizontal traces.

( ) Push the SAVE pushbutton. The indicator just
to the left of this pushbutton should go out.

NOTE: The DMO produces a very accurate display.
Your display oscilloscope may have a nonlinear dis-
play [such as raster distortion, etc), especially near
the edges and corners. If necessary, compromise dur-
ing the following adjustments to produce a best fit"
display.

( ) Use the Vertical Position control on your oscil-
loscope to center the trace by placing the refer-
ence center line (.8 division after the word
Trigger" in the center of the screen) so it is
on the center graticule line. If the line preced-
ing the "No Trigger message does not lay on
the top graticule line. adjust Output Cal con-
trol R506 on the display logic circuit board
of the DMO until it does. NOTE: If you are
using an oscilloscope that does not have an
8 x 10 graticule, use its position controls to
shift the display the proper number of divi-
sions on the screen. If you have a 6 x 10 divi~
sion oscilloscope, for example. move the refer-
ence line down so it is one division below cen-
ter. Then position the line preceding the No
Trigger" message on the top graticule line.
When you recenter the reference line and per-
form the remainder of the adjustments, the
DMO will be properly calibrated. The mes-
sage, however. will be off screen.