Reference Voltages; Buzzer Circuit; Reset Rom Circuit (Pcb Version <8 Only) - Fluke ScopeMeter 123 Service Manual

7. Supply a 15.6 kHz square wave of 20V (+10...-10V) to Input A, and Input B.
8. Check:
a. TP308 (TVOUT) for 15.6 kHz, -0.8...+0.6V pulse (square wave) bursts (see
figure below).
If not correct, N301 may be defective.
b. TVSYNC, on R392/R397, for 15.6 kHz, +2.6...+3.3V pulse bursts.
If not correct, V395 may be defective.
c. TP311 (ALLTRIG) for 15.6 kHz, +3.3...0V pulse bursts.
If not correct, N301 may be defective.
d. TP433 (TRIGDT) for 0...+3.3 pulses.
If not correct, TRIGQUAL may be not correct.
e. TP338 (TRIGQUAL) for 0...+0.6V pulses, width 70 µs, frequency about 2 kHz.
If not correct, D471 may be defective.

7.5.9 Reference Voltages

1. Check:
a. TP306 for +3.3V, TP307 for +1.23V
If not correct check/replace V301, R307, C3112, P-ASIC N501.
b. TP301 for +1.6V
TP302 for +0.1V
TP310, see figure below (in ROLL mode TP310 is zero).
If not correct, check/replace REFERENCE GAIN circuit and T-ASIC N301.
TP310

7.5.10 Buzzer Circuit

1. Press
2. Short circuit Input A to COM. The buzzer is activated now.
3. Check TP496 for a 4 kHz, 0...3V square wave during beeping (+3 V if not activated).
4. Check TP495 for a 4 kHz +3...-30V square wave during beeping (TP495 is +3V if
the beeper is not activated).
7.5.11 Reset ROM Circuit
1. Check TP486 for 3V, or ≅+12V if a power adapter input voltage >19V is supplied
15.6 kHz
TP303 for -1.23V
TP304 for +3.3V
≈ 800 ms
and select
MEASURE on A : CONT
(PCB version <8 only
≈600 ms
+1.2V
-1.2V
)
)
)
)
Corrective Maintenance
7.5 Miscellaneous Functions
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