Fixes for Glitches

Reverse Video Display

The most common indicator of a failed tuning procedure is the reverse video display of a receiver parameter on the Display monitor. In such cases the actual value will be shown in reverse video underneath the demand value. Most commonly this happens with the mixer currents. Occasionally the Gunn fails to lock.

The usual remedy is the ICL command

ICL>rxb_auto

which simply tells the computer to try tuning again using all of the present demand values. It is not necessary to do a be] DAS setup after the auto command.

"Receiver is not fully tuned"

Occasionally a message appears on the TSS's VAX screen stating "Gunn is locked, but receiver is not fully tuned". This may be a valid message, and the state of the receiver should be checked by referring to the Display screen(s). Often the last three of the eight debug indicators are set to "F" in this situation, and it appears that the receiver is in fact fully tuned, but the information has failed to reach the micro. At such times, the message appears when, in fact, the Display terminal indicates that all parameters are otherwise at their nominal values - i.e. there are no reverse video displays. In such cases, you may ignore the message and continue, or to be sure that you haven't missed a real fault on the Display terminal, the rxb_auto command should quickly remove this message.

Incorrect Demand Values

The demand values to which the computer sets parameters can be incorrect or inaccurate. This can happen in a number of ways. The original LUT values may have been overidden by manual adjustments in the receiver cabin or by entries from the Display terminal menu. In any case, if you suspect this to have happened, type

ICL>rxb_retune

This command refreshes the LUT values and restarts the automatic tuning without changing the frequency or configuration. Unlike the fe] command it does not require a be] command to set up the DAS.

Failure to set Mixer Current for Single Polarity Chan A Tuning

At present, due to a bug we have been unable to trace, mixer A cannot be tuned single polarity in fully remote mode. In single polarity mode, the computer does not correctly set the Channel Mode switch on the Modulator Module. Attempts to do this will result in an incorrect (i.e.reverse video) mixer current (usually 40 instead of 20 microamps). For this tuning to succeed the Modulator module must be put into Local mode and the Channel mode switch toggled up to the A position.

Irrational Performance

If the computer control of the receiver is tangled, locked up or otherwise irrationally unsatisfactory, there are several approaches. Experience has shown that the simplest fix is to issue a fe] command at a distinctly different frequency. Then, when the ICL prompt reappears a second fe] back to the desired frequency.

Alternatively it may be necessary to reboot the microcomputer, kill and reload the RxB I-Task. The command

ICL>rxb_reboot

is intended to do this. Alternatively, it may help to reset the microcomputer in the receiver cabin. Note that either of these rebooting procedures will cause both arms of the DBI to home and then reposition. This procedure takes a few minutes and the receiver cannot be tuned while it is occurring. Progress of the positioning can be monitored on the PF2 screen of the Display terminal or by watching the process in the cabin.

Failure of Auto-Tuning

If the auto-tuning procedure fails, it will be necessary to manually tune the receiver. This is most likely to happen near the limits of the tuning range where parameter settings are critical. For the recommended procedure, please refer to the section on Manual Tuning.