I have the wonderful spectrum analyzer 8564 E. Only when turning off the light spot is not suppressed. You see a roughly rectangular light field that fades in 1-2 seconds. What could I investigate for lack of circuit?
This is a very old question and may have been answered a while ago, but here is some input for anyone else that may run into this.
A spot on the CRT after power off is not normal, however is somewhat common as the analyzer ages. A simple explanation is, the CRT high voltage lead (aquadag lead) is always charged with a very high positive charge (+9000V), even at turn off, which slowly bleeds off. The cathode, which has a high voltage charge (-2450), and the control grid, which also has a negative charge approximately -100 volts more negative (-2550), will collapse when the unit is turned off. If the control grid goes more positive than the cathode, which is heated and still trying to emit electrons, then some transmission through the CRT is possible. At this point, there is no blanking pulse because the power is off. Stray electrons hitting the screen may illuminate it for a brief moment during this collapse if the control grid goes more positive than the cathode when it shuts off. As the aquadag voltage fades, the spot may slowly fade.
It's real hard to say what is actually causing the timing of the charge collapse but this is why there is illumination after the power goes off. The usual problem is the CRT itself. However the A17 driver could also cause this. Lastly, a word of caution from the service guide:
WARNING The A6 power supply in 8562E and 8562EC instruments, and the
A6A1 high voltage assembly in 8562E instruments, contain
lethal voltages with lethal currents in all areas. Use extreme
care when servicing these assemblies. Always disconnect the
power cord from the instrument before servicing these
assemblies. Failure to follow this precaution can represent a
shock hazard which may result in personal injury.
The voltage potential at A6A1W3, in 8562E instruments, is +9 kV.
If the cable must be disconnected, always disconnect it at the
CRT with caution! Failure to properly discharge A6A1W3 may
result in severe electrical shock to personnel and damage to the
instrument. See procedure 2 in Chapter 3.
Do not discharge the CRT second anode directly to ground,
with the A6A1 high voltage cable connected. This can damage
the A17 CRT driver assembly. Always discharge through a high
resistance, such as a high voltage probe.
Always use an isolation transformer when troubleshooting
either the A6 power supply or the A6A1 HV module. When using
an isolation transformer, connect a jumper between A6TP101
and A6TP301. This connects the circuit common to earth
ground. Remove this jumper when the isolation transformer is
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