Purpose

Basic steps to starting up B3

	Actions taken	Notes
	Start up the B3 monitor. Open up a new DECterm, identify yourself, and at system prompt type the command @rxb_screen	The screen will appear corrupted for a while until the B3 task is fully loaded. This is normal. The B3 task should be killed first if it's already running.
	If you plan to proceed with a reboot of B3, first issue smu_kill from ICL in your main DECterm window.	If you don't, the SMU task will fall over.
	Check in the cabin that B3 is in a normal state	Make sure all 5 local/remote switches on the electronic modules are in the remote position, especially. Check that the inner shield temp is around 17 K. Do visual check in cabin for loose items.
	Reboot B3 and wait for it to finish.	It is important to make sure that the reboot works. Within a few seconds the DBI arms should start to move; wait until all the DBI lights are green; this will take a couple of minutes.
	Back downstairs, send the DBI to the correct position.	Use the B3 PF2 (DBI) screen and set the correct position using the commands at the bottom. Arm 1 should be set to 13.5 for SSB operation and 3.5 for DSB. This should avoid DBI timeouts and incorrect positioning of the DBI when the first tuning command is issued.
	Start up the B3 VAX software: from another decterm window, at the ICL> prompt enter fe] and provide tuning parameters as prompted.	Supply desired sky frequency, velocity, sideband, dual/single channel and single/double sideband operation
	From the B3 monitor screen choose "debug" mode to watch progress of tuning.	A string of 8 characters in the lower left of the screen will indicate progress; "N" means "new" value supplied, "S" means succeeded, "T" means "tuning", and "F" indicates failure.
	Check important parameters are correct, especially Gunn Voltage (6.0 volts) and DBI arm 1 position (~13.5 for SSB, ~3.5 for DSB operation, +/- a few tenths.)	The Gunn voltage can be found on screen 1 (use PF1) and the DBI on screen 2 (PF2).
	After every major tuning, check demanded vs actual LO frequency.	Compare LO frequency shown by EIP counter in cabin with demanded value on screen 1 of monitor.
	Load CBE, set SMU to sensible values. Point and focus on a spectral line standard source.	Check IF power LED's for obvious instability in either or both channels.
	Load DAS backend with, say, 250 or 500 MHz b/w.	Wait for autolevelling to be complete; adjust IF2 if necessary.
	Do calibration and check results are sensible.	Sensible Trec values will be in the range 200-300 K (SSB mode) or 100-150 (DSB) over most of the band.
	Go to standard spectral line target and do a 2-minute integration in recommended manner.	Check result against standard, or consult representative spectra if necessary. An error in intensity of +/- 10-15% is OK. A different line shape would be suspicious, however.

Explanations, and suggestions if things don't do what you expect

B3 monitor screen and terminal server. The initial appearance of the B3 monitor screen is quite garbled. It needs updated information from the B3 micro, and this is not available until the VAX B3 task is completely loaded or until the B3 micro is rebooted. Sending multiple PF1 etc commands to the screen will not help; best to just be patient until the rest of the system is loaded. If the B3 monitor screen does not appear at all, it is most likely that the terminal server in the cabin needs to be reset. Do this by unplugging the power from the server and plugging it back in. Also check that connections to the server are made correctly while in the cabin.

The SMU task will fail if you reboot B3's micro without killing the SMU task first. This happens because they are on the same bus.

Visual checks of B3. Use temperature monitor to check the LHe can and inner and outer shield temperatures They should be about 3.1, 17 and 65 K; if not call someone. The inner shield is the most critical number. Also check the HEMT bias voltages via the module; for both HEMT's they should be 2.5, 2.5 and 4.5 volts for the three stages. The latter are currently not being reported to the monitor screen (values are all 0.0). Also, after daywork do check for things which might be left in, or fall into the beam (e.g. the plastic helium relief tube), and for things which are left loose in the cabin, which can fall into B3.

Tuning parameters should be provided in the usual way. In SSB mode the sideband is not critical except near the tuning extremes, so the other sideband can be used if one does not produce an acceptable result.

Debug mode can be turned on from the B3 monitor screen by typing "q" until you reach the base commands; then choose "o" for "Other" and "d" for "Debug". Tuning progress proceeds from left to right through the 8 stages, beginning with the Local Oscillator (indicated by "LO"), and ending with the mixer currents ("MA", "MB").

The DBI arm 1 position sometimes causes B3's tuning to be incorrect, as it may stall at an intermediate position, appropriate neither for SSB or DSB. Check the PF2 (DBI) screen; the value should be fairly close to 13.5 (SSB) or 3.5 (DSB), give or take a few tenths. If necessary, or if in doubt, send arm 1 to home, then back to correct rough position, and finally issue fe] command again. An incorrect DBI position results in poor rejection of the unwanted sideband in SSB mode; and one clue is that the Trec value is not as expected. The Gunn voltage is found at the extreme left of the PF1 screen; it should normally be set to 6.0 volts; sometimes it may arrive at 9.99, or worse, 0.0 volts. If so use the commands at the bottom of the B3 screen to adjust it.

The EIP counter reads the LO frequency in GHz. Although it is not locked to an external frequency standard, its internal standard is accurate to a small fraction of a MHz. The fault we have seen is that the demanded (seen on the PF1 screen) and actual (seen on the EIP) differ by 50 MHz. Until we fix this problem, it's important to check that the demanded and actual frequencies agree. The EIP is permanently connected, but it may be switched off. To use it, switch on power, and choose either "band", "4", "3" or (for LO > 90 GHz) "band" "4", "4" (the lighted indicator will read either "43" or "44"). Preferred fix at present is to change sidebands if possible. You can also try increasing or decreasing the manual LO attenuator and retuning.

The IF power levels as seen on the LED bar graphs should be at a detectable level. If the level is very small, you have any one of a number of problems (first check that B3 junctions are actually turned on, for example, and that the receiver actually claims to have finished tuning). Look closely at the LED bars; if either of the levels are fluctuating then the mixer outputs may well be unstable. Possible cures for this include changing the mixer bias voltage usually lower by 0.1 volt (use the commands at the bottom of the B3 screen while1 watching the number change on the PF3 (mixer) screen, or if this doesn't work, doing a full restart of B3 including a reboot of the micro. If one channel of B3 is still much more stable than the other select that channel for pointing/focus if the observer plans to live with the instabilities.

For most test sources 500 MHz bandwidth is fine. When the DAS is loaded, the IFS will autolevel the power in both channels to around 30-40% of the maximum. In single-channel mode (extreme wideband) you will have to adjust the IF2 level yourself, as the IF Switch does not do it.

If the Trec values look wrong, say, you get 80 K in SSB mode, then something is amiss. Double check that the DBI arm 1 is in the right position, via the PF2 screen. See above for notes on that.

If the Tsys values are completely at odds with you knowledge of sky conditions, check the cold load termination window on the dewar for icing (this can happen if the last day or so has been very humid, and the fan blowing air on the window has failed, but it's not a very frequent problem.)

Standard spectra can be found in the usual places. If no data entry for your particular line is found, use the "representative" spectrum (once these have been restored to the Web). One should check to see if there is a spectrum for your proposed source before observing it. Intensities should not be different by more than about 15% if the receiver is reasonably well calibrated. An obvious change in line shape may be due to a pointing offset, a focus offset, or a bad beam shape, since it usually means you are observing a different part of the source distribution.

Final resorts - the reboot and the big reboot

The procedure I suggest is as follows:

1. ICL> instruments_kill (if B3 task is running)
2. Leave the B3 screen running
3. Go upstairs and firmly press the micro reboot button
4. Wait, and watch the DBI module lights dance while the DBI arms check home and end stops.
5. If nothing of the sort happens, firmly press the reboot button a second time. This usually works.
6. Wait for the DBI to finish its journeys to and fro; then double-check all looks OK, and leave the cabin.
7. ICL> fe] (i.e. go back to the first tuning step, above)

Sometimes we find a bigger hammer is necessary. In between steps 2 and 3 do:

• Make sure junctions are turned off (mixer lights are red).
• Turn off power to the electronics rack.
• Slide under the electronics rack, and remove the plug from the back of the micro power supply. It helps to be slim here!
• After a few seconds, replace the plug.
• Turn on power to the electronics rack.