Tektronix 2445, Instruction Manual

Page: 36 / 351

Operating Information—2445 Service
The locations and types o f information displayed under
normal operating modes are illustrated in Figure 2-8.
NOTE
Other inform ation is displayed when the instrument
is in a diagnostic mode or has experienced a fault.
The diagnostic displays are explained in the "M ain­
tenance" section o f this manual.
i f the bottom row o f the readout contains dots in
the norm ally blank spaces, a wrong calibration
constant has been encountered. The instrument must
be readjusted to remove the incorrect calibration
constant from the EA ROM.
Each of the scale-factor displays appears when the
respective vertical channel or sweep is displayed. When X-Y
mode is selected, the Channel 1 scale factor is displayed,
and CH 1 X appears in place of the A Sweep scale factor.
Special characters or abbreviations are displayed to
indicate GND or AC coupling of Channel 1 or Channel 2
signals, ADD, CH 2 INVERT, Vertical bandwidth limited,
or HOLDOFF not set to minimum.
The Trigger-Level readout shows the signal voltage
(at the probe tip o f encoded probes) that w ill initiate
the sweep. The readout appears only if the following con­
ditions exist: a single vertical channel is selected as the
trigger source, the vertical input coupling is not AC, the
VO LTS/DIV VAR control of the source channel is in the
calibrated detent, and trigger coupling is either DC or
NOISE REJ.
A question mark may appear in a DLY (delay time), a
A t (delta time), or a 1 /A t readout when the SEC/DIV
knobs are unlocked (not w ith cursors). This indicates that
either the delay time (or one o f the two delay times) is set
at less than 0.5% of the maximum delay or the B TR IG ­
GER MODE is set to TRIG AFT DLY. A question mark
w ill also appear in a 1/At display readout when the
difference between the two delays (or the distance between
the tw o cursors displayed when the A and B SEC/DIV
knobs are locked together) is less than 1% of full scale.
The 50 £2 OVERLOAD display appears if excessive signal
is applied to either the CH 1 or the CH 2 input connector
while 50 £2 DC input coupling is selected. The readout w ill
return to the normal display when the input coupling of the
overloaded channel is switched.
T R IG G E R LEVE L IND IC A TO R 50 ft O VE R LO A D SWEEP D E L A Y T IM E
38 3 2 -1 0
2 -1 4
Figure 2-8. Readout display locations