![Tektronix 485 Instruction Manual Download Page 65](http://html1.mh-extra.com/html/tektronix/485/485_instruction-manual_1078906065.webp)
Calibration-485/R485 Service
72. O P TIO N A L - CHECK C A L IB R A T O R O V E R
SHOOT, R IN G IN G , and R IS E TIM E
NOTE
These characteristics have been factory verified to
specifications. Due to their long term sta b ility (failure
to perform is m ost lik e ly the result o f catastrophic
failure) o n ly a qualitative check is done here. The
Calibrator overshoot and ringing on the 485 is
compared to th a t observed from the Tunnel Diode
Pulser.
a.
Set CH 1 input to 50 S2, DC coupled; TIM E/D IV to
1 ns; VOLTS/DIV to 20 mV.
b. Connect the Type 106/Tunnel Diode Pulser through
a 2X BNC attenuator to the CH 1 input (approximately
5div step). Observe the reference " f la t" portion following
the positive step.
c. Connect a 5X BNC attenuator to the CAL 5 V output
and connect this signal to CH 1 input (5 div step). Again,
observe the " fla t" portion following the positive step. This
response should be within ±0.1 div (±2%) of the reference
" fla t" portion observed in b.
d. Check positive edge risetime of the Calibrator as
observed on the 485. Should be less than 1.4 ns.
73. ADJUST A T R IG G E R (Board N ext to Atten
Shield on Bottom of Oscilloscope)
a. Set HORIZ DISPLAY to A; A TIM E/D IV to 10
ps/
div; A COUPLING to AC; A TRIG HOLDOFF to NORM;
A SOURCE to INT; A SLOPE to +; SWEEP MODE to
NORM.
b. Set LEV CTR, R725 (R1025)1, to midrange; A TRIG
SENS, R755 (R1055), CCW; ARM TD, R765 (R1075), CW;
OUT TD, R775 (R1065), CW; LEVEL, R720, (R1020) CW.
Apply one division of 50 kHz reference signal from the
Type 191 Signal Generator to the CH 1 input.
c. Turn ARM TD CCW until trace disappears. Note
position of pot.
d. Adjust LEVEL for a stable display.
e. Turn ARM TD further CCW until trace disappears.
Note position of pot.
f. Adjust ARM TD pot halfway between positions noted
in steps c and e.
g. Disconnect coax from J763 (J1063 for B trigger).
J763 is rear white and brown coax on A trigger board
(J1063 is rear white and brown coax on B trigger board).
1 Circuit numbers in parenthesis pertain to B trigger adjustments, see
step 74B.
h. Monitor the voltage at the OUT TD test point
(located near the OUT TD control) and adjust the OUT TD
control R775 (R1065) until the trace just disappears.
Record this voltage.
i. Reconnect the coax to J763 (J1063).
j. Adjust the OUT TD control CCW until the trace just
disappears again. Record this voltage.
k. Subtract the voltage in part j from the voltage
recorded in part h. M ultiply the result by 0.8 and add this
quantity to the voltage recorded in part j.
l
. Adjust the OUT TD control to produce a reading that
equals the final amount calculated in part k.
m. Adjust TRIGGER SENS, R755 (R1055) until display
cannot be triggered on 0.15 div of signal by rotating the
LEVEL control, but can be triggered on 0.18 div of signal
by rotating the LEVEL control, (to set signal amplitude to
0.15 or 0.18 div, first adjust the generator amplitude for a
display of 1.5 or 1.8 divisions, then increase the VOLTS/
DIV setting by a factor of 10). Increase generator signal to
produce a two division display.
n. Adjust LEV CTR for a stable display with LEVEL
knob dot positioned at top center (12:00 o'clock).
o. Switch trigger COUPLING to DC, adjust INT TRIG
DC BAL, R560 (located on Vertical Amplifier board), for
stable triggering with display vertically centered on grati
cule.
p. Apply signal to CH 2 input. Check for triggering
within 0.5 divisions of graticule center with SLOPE in +
and — positions when VERTICAL MODE is set to CH 1
and CH 2; and within one division of graticule center when
VERTICAL MODE is set to ADD. Disconnect signal from
485.
74A. ADJUST E X T E R N A L TR IG G E R LEVEL
C E N TE R IN G
a. Set A trigger SOURCE to EXT; A LEVEL knob dot
to 12:00 o'clock.
b. Connect the Type 191 Signal Generator to the
A EXT TRIG connector. Hold the A EXT TRIG button in,
and adjust the Type 191 for a 2 division display of 50 kHz
signal.
c. Adjust R830 (IDENT) while depressing the A EXT
TRIG button, so the trace starts at an equal distance above
and below graticule center when switching the A Trigger
SLOPE switch from + to —. Release the A EXT TRIG
button.
d. Remove the signal from the A EXT TRIG connector,
and apply it to the CH 1 input.
REV. D, AUG. 1975
5-21
Summary of Contents for 485
Page 3: ...485 R485 rviice T h 5 0 Oscil oscope ...
Page 74: ...Rackmounting 485 R485 Service 6 6 ...
Page 128: ...485 R485 Service MAR 1979 5 m V B A L ADJ ...
Page 152: ... 0 iT s i ...
Page 164: ...2S2 n eKn s e s 5 4 85 Os c illo sc o p e REV F A U S 1 9 7 7 I 1 9 3 5B POWER SUPPLY 773 ...
Page 178: ......
Page 179: ...485 R485 OSCILLOSCOPE REV D MAR 1977 ...
Page 184: ...REV C MAR 1976 485 R485 OSCILLOSCOPE ...
Page 197: ......