Fluke 39 - Watts Measurements (Volt-Amps); Harmonics Measurement Accuracy (Cursor Data); Frequency Measurement Accuracy

39/41B
Service Manual
5-8
• SRD (U2-38) labeled ‘DOUT’ - serial data received from the MUX in U3.
When the instrument is collecting data in normal operation mode, the above four
waveforms can be observed with the following timing.
SCK
CS2
SRD
SC0
111098765432101110987654321
AMPSVOLTS
When SC0 is low, SRD is the output of the volts a/d converter and amps when high.
241,824 Hz
426.62 ns
4.135 ns
10,072 Hz
t18i.eps
Note
When the instrument is in normal operation, it will collect data for about
234.6 ms when the input frequency is >
≈ 10Hz, then process data for ≈ 80
ms with the process repeating. With an input frequency <
≈ 10Hz, it will
collect data for 469.2 ms, then process data for
≈ 80 ms with the process
repeating.
If SC0, SC2, and SCK are not present and the Tester is collecting data in normal
operation (not in HOLD or memory mode), powering on properly, responding to key
presses properly, and displaying the correct screen, the DSP (U2) may be defective.
If SRD is not correct, either the A/D converters may not be generating DOUT or U3 may
not be producing the SRD signal correctly.
2. Check for proper communication between U3 and the A/Ds (U14 and U15). U3 has
four control lines to the a/d converters:
SCK*
DOUT_VOLTS
DOUT_AMPS
CS_AD*
NN9876543210123456789NNN
NN9876543210123456789NNN
241,824 Hz
r19i.eps