Circuit Operation; Power-Up Sequence - Fluke 39 Service Manual

The power supply voltages for the Tester are derived from four "C" cell batteries. The 4
to 6 volt dc source generates 6 separate voltage sources to power digital, analog, and
display circuitry. The "C" cell batteries typically provide 48 hours of Tester operation.
The Input Conditioning section filters and controls the amplitude of the incoming signals
to the a/d converters. Signal amplitude is adjusted for maximum dynamic range of the
a/d converters. The anti-aliasing filter eliminates any signal components that are more
than one half the sampling frequency. Without this filter, some signals may be
interpreted incorrectly.
There are two a/d converters in the Tester. One for the volts input and the other for the
amps input. These a/d converters quantize the input signals to digital or numeric values,
so the Digital Signal Processor (DSP) in the digital kernel can read and process the
information. Both converters sample the input signals at a 10 kHz rate.
The digital kernel is basically a small but fast computer system. It has three input
sources: sample data from the a/d converters, user input via the keypad, and user input
through the serial optical interface. The display is the primary output device, but the
digital kernel also controls the input conditioning and sends data to a PC or printer
through the optical interface.
The DSP takes the a/d converter samples and stores them in static RAM (SRAM). When
enough data samples have been taken, the DSP calculates the values and waveforms for
display. No matter what screen is presently on the display, the calculations for all display
readings are always performed. The display routines determine which screen the user has
selected and displays the appropriate data for the screen requested. All values and
waveforms are the result of thousands of calculations performed by the DSP.
The optical interface communicates with a PC or printer, and it provides a sufficient
voltage standoff for safety reasons. The Fluke PM9080 interface cable is required to
complete the interface to a PC or printer.

2-3. Circuit Operation

To help you understand the circuit operation, the power-up and normal operation
sequences are explained below.
2-4.

Power-Up Sequence

1. The power button is pressed.
2. The power supply settles to 3.3 volts about 11 ms after the On button is pressed.
3. The reset line (U2-123) changes from high to low about 30 ms after the On button is
pressed.
4. The DSP automatically downloads 512 words (1,536 bytes) of instrument operating
code to instrument RAM from the EPROM (U4) immediately after coming out of
reset.
5. The DSP activates the power-on signal (U2-19) to a high state about 20 ms after
coming out of reset.
6. The remaining instrument operating code (about 14K words or 42K bytes) is
downloaded from the EPROM (U4) to the SRAM (U5,6,7). This should take about
70 ms or be complete about 100 ms after initial power-up.
7. While the code is being downloaded, a checksum is being calculated. If the check-
sum is correct, U2-17 goes high. If there is a problem downloading the program, the
unit powers itself off at this point.
Theory of Operation

Circuit Operation

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