Fluke NetDAQ 2640A, Service Manual

Page: 191 / 260

Diagnostic Testing and Troubleshooting
Troubleshooting the Instrument
5
5-27
A1 Main PCA Troubleshooting 5-21.
The following paragraphs provide troubleshooting hints for the A1 Main PCA. Use this
material in conjunction with Chapter 2, “Theory of Operation.”
WARNING
To avoid electric shock, disconnect all channel inputs from the
instrument before performing any troubleshooting operations.
Troubleshooting the A1 Main PCA Digital Kernel 5-22.
When the instrument is first powered, the resident RAM portion of the A1U1
microprocessor begins to initialize the digital kernel. This activity may be monitored at
one of the A1U1 microprocessor chip select outputs, for example, FLSH* at A1U1-128,
or RAM* at A1U1-127. (It might be easier to measure signals at places other than the
pins of the A1U1 microprocessor; for example, measure A1U1-128 at resistor A1R144.)
If there is brief chip-select activity and then the activity stops, this indicates that the
A1U1 microprocessor tried to start operation, but one or more of the outboard devices
did not respond and the A1U1 microprocessor was unable to continue initialization. If
there is no chip-select activity when power is first applied to the instrument, then the
A1U1 microprocessor may have been damaged by static electricity.
If the problem seems to be in the outboard devices, then probe them with a logic
analyzer or oscilloscope looking for missing signals or dc power, or by touch to find a
device that is excessively warm. (Be careful to touch only the case of the device and not
the pins.) These devices include A1U21 Flash Memory, A1U20, A1U30, A1U34,
A1U35 Static RAM, A1U11 Real-Time Clock, A1U10 Power Monitor, A1U12 Flash
Programming Power Supply, and related logic devices such as AND gates, OR gates,
and inverters.
Check the A1U1 crystal frequency at A1TP11 to make sure there is a clock input to the
A1U1 microprocessor. The crystal frequency should measure 15.36 MHz.
Check the jumper A1W3 near A1U21 Flash Memory and make sure it is in place. If this
jumper is missing, the instrument will appear completely dead. Check all the jumper
positions, as shown in Table 5-12.
Table 5-12. A1 Main PCA Jumper Positions
Jumper If Missing If in Place
W1 A1U1-109 enable PB1/disable
IACK6* A1U1-109 disable PB1/enable
IACK6*
W2 A1U21 programming power via
Vpp A1U21 programming power via
Vcc
W3 Flash disabled (dead Instrument)
Flash enabled
W4 Boot Baud rate 19.2k Boot Baud rate 38.4k
W5 A1U1-108 enable PB0/disable
IACK7* A1U1-108 disable PB0/enable
IACK7*
Normal jumper position is shown in bold.