Fluke PM6690, Service Manual, Page: 32 / 200

– Optional main inputs replacing corresponding front
panel inputs
OUTPUTS:
– Internal reference 10 MHz (BNC)
Prescaler Circuit Board
There are several different optional prescalers available with
different frequency ranges. The prescaler is located on a sepa-
rate circuit board that is connected to the main circuit board
with a PCB connector.
A typical prescaler consists of a limiter, an amplifier, a fre-
quency divider, and a detector. The limiter and the amplifier
condition the input signal so that the amplitude to the divider
is constant. The divider scales the input signal so that it can be
handled by the measuring logic on the main circuit board. A
detector switches off the output signal from the divider if the
input level is too low for the divider to work correctly (divid-
ers often oscillate without input signal).
Test Routines
Built-in Test Routines
The test routines are those accessible via the USER OPT key.
– Press USER OPT
®
Test
®
Test Mode
– Choose one of the five alternatives:
1. All - Perform the four basic tests below in sequence
2. Memory - Test RAM and ROM
3. Logic - Test measuring logic circuits
4. Display - Test the graphic LCD display
5. Interface - Test the two standard interfaces, GPIB and
USB
Power-On Tests
Certain tests are automatically performed at power-up. Errors,
if any, are reported on the display.
4-10 Hardware Functional Description
Limiter
Amplifier
1
Amplifier
2&3
Amplifier
4&5
AGC1 AGC2
Voltageregulator
Dividers
Detector
Not C
Test go
Input
Figure 4-6
Typical prescaler option, block diagram