Troubleshooting, Communication Problems

HYDRA

Service Manual

7-12. Troubleshooting

7-13. Power-Up Problems

The following discussion identifies probable fault areas if the installation of an IEEE- 488 Option causes power-up failure for the instrument. The problem is probably a short on A5J1; the Microprocessor on the Main Assembly is prevented from accessing ROM and RAM correctly.

∙First check if VCC is shorted to GND on the IEEE Assembly.

∙The short may also be caused by an interface signal to either VCC, GND, or another interface signal. The logical signals to check are D7 .. D0, A2 .. A0, RD*, IEEE*, WR*, E, RESET*, and IRQ2*.

∙The short may be due to a CMOS input that has been damaged due to static discharge; the short is then detectable only when the circuit is powered up. Use an oscilloscope to check activity on each of the interface signals. Verify that signals are able to transition normally between 0 and 5V dc.

7-14. Communication Problems

7-15. Failure to Select IEEE-488 Option

IEEE-488 Interface selection procedures are described in Section 3 of the Hydra User Manual.

If the IEEE-488 option is not detected by instrument software, there may be a problem with the OPS* signal. The IEEE option grounds the OPS* signal (A5J1-22), which is normally pulled up to VCC on the instrument Main PCA. The Microprocessor determines that the IEEE-488 option is not installed if OPS* (A1U4-29) is high during the power-up option detection.

7-16. Failure to Handshake on IEEE-488 Bus

After power-up or when the active computer interface is changed from RS-232 to IEEE- 488, the Microprocessor sends six write cycles to initialize A5U1. The IRQ2* interrupt is then enabled, and the serial poll status byte is initialized. At this point, the IEEE-488 option is ready to respond to transactions on the IEEE-488 bus.

7-17. Failure to Enter Remote

If the IEEE-488 option does not enter remote, check that the remote/local control circuit is operating properly. When the IEEE-488 option is the active instrument interface, the remote/local control state is polled by the Microprocessor approximately every 400 ms. Normally, A5U1-4 goes low for approximately 800 ns during the read cycle that checks the state of A5U1. If D(0) (A5U1-11) is low during the read cycle, A5U1 is in the local state. If A5U1-11 is high during the read cycle, A5U1 is in the remote state. When A5U1 indicates that it is in remote, the REM indicator on the display is turned on.

7-8

2635A, 2625A specifications

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Fluke 2635A, 2625A Troubleshooting, Communication Problems, Failure to Select IEEE-488 Option

Models: 2635A 2625A