Fluke 123B/S Service Manual - Page 126

Trigger Functions, CAP ., VDC .

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123/124 Service Manual 2. Press and select MEASURE on A: I CAP . Verify TP156 for +0.3 ... 0V pulses (repetition rate 100...200 ms): Zero scale (open input): pulse width approximately 30 µs. Full scale (for example 500 nF): pulse width approximately 25 ms. If not correct, most probably the C-ASIC N101 is defective. If correct, continue at Section 7.5.8 Trigger functions (pulse width is measured via the T-ASIC). 7.5.8 Trigger Functions 1. Press and select MEASURE on A: I VDC . 2. Press and select INPUT A: I DC | NORMAL | INPUT B: I DC | NORMAL 3. Press to select the SCOPE INPUTS menu. Press to select the TRIGGER menu, and select: INPUT: I A or B | SCREEN UPDATE: I FREE RUN | AUTO RANGE: . I >15HZ Press to open the SCOPE INPUTS menu. Press to open the SCOPE OPTIONS ... menu, and select: SCOPE MODE: I NORMAL | WAVEFORM MODE: I NORMAL. 4. Supply a 1 kHz sine wave of +/- 3 divisions to Input A, and Input B. 5. Check: a. TP156, TP256 for a 600 mV (6 div. x 100 mV/div), 1 kHz, sine wave; the DC level depends on the trace position. If not correct, C-ASIC N101/N102 is probably defective. b. TP321, TP322 for 1.1...1.9V DC (move the trigger level from top to bottom). If not correct check the PWM circuit, see Section 7.5.8. c. TP311for a 0...+3.3V, 1 kHz square wave when the trigger level is at the middle of the trace). Change the trigger level, and verify that the duty cycle of the square wave changes. If not correct T-ASIC N301 may be defective. d. TP433 (TRIGDT) for 0...+3.3V pulses. Pulse width: 4...10 µs for time base 2 µs/div and faster; >40 µs for time base 5 µs/div and slower; pulse width increases with time base. e. TP336 for +0.6...0V pulses, TP436 for +3.3...0V pulses; the pulse width is about 40 µs...10 ms. If not correct, check the RANDOMIZE circuit, see Section 7.5.15. f. SMPCLK_B (N301/38) for a 5 MHz (time base ≥ 10 ms/div) or 25 MHz (time base < 10 ms/div) clock signal (3.3V). Check SMPCLK_B on both sides of R339. 6. To test video trigger press to select the SCOPE INPUTS menu. Press to select the TRIGGER menu, and select INPUT: I VIDEO on A... From the VIDEO TRIGGER submenu select: SYSTEM: I PAL | LINE: I RANDOM | POLARITY: I POSITIVE Press to open the SCOPE INPUTS menu. 7-14

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123/124
Service Manual
7-14
2.
Press
and select
MEASURE on A:
■
CAP .
Verify TP156 for +0.3 ... 0V pulses (repetition rate 100...200 ms):
Zero scale (open input):
pulse width approximately 30
µ
s.
Full scale (for example 500 nF):
pulse width approximately 25 ms.
If not correct, most probably the C-ASIC N101 is defective.
If correct, continue at Section 7.5.8 Trigger functions (pulse width is measured via
the T-ASIC).
7.5.8 Trigger Functions
1.
Press
and select
MEASURE on A:
■
VDC .
2.
Press
and select
INPUT A:
■
DC | NORMAL | INPUT B:
■
DC | NORMAL
3.
Press
to select the
SCOPE INPUTS
menu.
Press
to select the
TRIGGER
menu, and select:
INPUT:
■
A
or
B
|
SCREEN UPDATE:
■
FREE RUN | AUTO RANGE: .
■
>15HZ
Press
to open the
SCOPE INPUTS
menu.
Press
to open the
SCOPE OPTIONS ...
menu, and select:
SCOPE MODE:
■
NORMAL | WAVEFORM MODE:
■
NORMAL
.
4.
Supply a 1 kHz sine wave of +/- 3 divisions to Input A, and Input B.
5.
Check:
a.
TP156, TP256 for a 600 mV (6 div. x 100 mV/div), 1 kHz, sine wave; the DC
level depends on the trace position.
If not correct, C-ASIC N101/N102 is probably defective.
b.
TP321, TP322 for 1.1...1.9V DC (move the trigger level from top to bottom).
If not correct check the PWM circuit, see Section 7.5.8.
c.
TP311for a 0...+3.3V, 1 kHz square wave when the trigger level is at the middle
of the trace).
Change the trigger level, and verify that the duty cycle of the
square wave changes.
If not correct T-ASIC N301 may be defective.
d.
TP433 (TRIGDT) for 0...+3.3V pulses.
Pulse width:
4...10
µ
s for time base 2
µ
s/div and faster;
>40
µ
s for time base 5
µ
s/div and slower; pulse width increases with time base.
e.
TP336 for +0.6...0V pulses, TP436 for +3.3...0V pulses; the pulse width is about
40
µ
s...10 ms.
If not correct, check the RANDOMIZE circuit, see Section 7.5.15.
f.
SMPCLK_B (N301/38) for a 5 MHz (time base
≥
10 ms/div) or 25 MHz (time
base < 10 ms/div) clock signal (3.3V).
Check SMPCLK_B on both sides of
R339.
6.
To test video trigger press
to select the
SCOPE INPUTS
menu.
Press
to select the
TRIGGER
menu, and select
INPUT:
■
VIDEO on A...
From the
VIDEO TRIGGER
sub
menu select:
SYSTEM:
■
PAL | LINE:
■
RANDOM | POLARITY:
■
POSITIVE
Press
to open the
SCOPE INPUTS
menu.