Troubleshooting; General - Fluke PM6685 Service Manual

General

Quick Troubleshooting
The PM6685 is a highly integrated Frequency counter with dedicated
LSI counter circuits and microcontrollers that control the complete
units. The microcontroller can help you locate faulty parts by run -
ning test programs and generating stable signal patterns on t
he bus. If the microcontroller does not work or the fault is in a part of
the counter that cannot be accessed by the microcontroller, tradi -
tional troubleshooting must be performed.
Where to Start
After reading the safety instructions, continue with this chapter for
troubleshooting and repair instructions. When you have fixed the in -
strument, always do the Safety Inspection and Test after Repair, as
described later in this Chapter. Then do the checks in Chapter 2, Per -
formance Check. Recalibrate if required by following the adjustment
instructions in chapter 6, Calibration Adjustments.
Logic Levels
The PM6685 contains logic of four families. The levels for these
families are listed in the following table.
Positive
ECL
Supply voltage
Signal ground
Input voltage
High, V >+3.9 V
IH
Low, V <+3.5 V
IL
Output voltage
High, V >+4 V
OH
Low, V <+3.3 V
OL
Bias ref. voltage, V +3.7 V
BB
Table 5-2
Logic levels.

5-4 Troubleshooting

Troubleshooting
Negative CMOS
ECL
+5 V -5.2 V +5 V
0 V 0 V 0 V
>-1.1 V >+4 V
<-1.5 V <+1 V <+0.8 V
>-1 V >+4.9 V >+2.7 V
<-1.7 V <+0.05 V <+0.4 V
-1.3 V -
Required Test Equipment
To test the instrument properly using this manual, you will need the
equipment listed below. The list contains specifications for the criti -
cal parameters.
DMM
Oscilloscope
Signal generator
Power supply
BNC-BNC 50 W cables
Table 5-3
PROM Identification
There are two different PROMs in the PM6685, one on the main
PCB containing the instrument firmware, the other on the optional
GPIB board, containing the interface bus firmware.
They have labels with version designation of the traditional form
Vx.yz, where x, y, and z are digits. The last digit can be followed by a
single letter. The version numbers do not have to coincide, except for
the last letter. So the combination Vr.stE and Vu.vwE is valid,
whereas Vr.stE and Vu.vwF is not.
TTL
Operating Conditions
+5 V
Power voltage must be in the range of 90 to 260 VAC.
0 V
Introduction
>+2 V
-
Fig. 5-1
The troubleshooting strategy for the PM6685 is an integrated part of
the overall service strategy for the instrument. This instrument is hi -
Type
300 MHz 2-channel
Required test equipment.
GPIB(Level 10 )
INPUT AMPL IFIER(Le ve l 9)
D/A CONVERT E RS (Le ve l 8)
MEASURI NG L OGIC(Level7)
KEY BOARD (Level6)
INTE RNAL CONTROLS IGNALS & DIS PL A Y (Le ve l 5)
M ICROC O MPU T ER KERNEL (Level 4)
M ICROCONTROLLER (Level 3)
OSC ILL ATOR(Level 2 )
POW E RSUPPLY (L evel 1 )
Functional levels.
Performance
3.5 digits
3300 MHz
12 V/2 A
RG-58