As a lecturer, I hate multiple-choice questions where one has to
read the mind of the setter to find the answer to the question.

It's made all the more indirect and difficult if one doesn't have
the original question (doctor, my friend's got a headache...),
as I suspect is the case here: 'let discharge off' is not
Standard English - is it Good American, suitable for consumption
in a national test?

It sounds more like an unpleasant medical condition than
an electronic servicing procedure :-)

However, let us delve into the meaning and solution of this riddle...

I assume we are to discharge the energy in power supply capacitors
for safety prior to servicing: since the question explicitly states
a pc monitor I assume the examiner intends the EHT supply, rather
than just any off-mains switcher, but doesn't choose to name it.
I wonder if this vagueness is an intentional part of the assessment:
in other words, the candidate is being tested on the ability to
_recognise_ hazards as well as deal with them? If not, then it's
a poorly set (or poorly reported :-) question.

I believe the full safety procedure for high voltage electrical
supply equipment is Switch off, Isolate, Discharge, Ground.

What do we want to do - to remove residual EHT circa 25KV
in safety and know that we have been successful.

What do we need - an insulated resistive probe and voltage monitor.

How do the supplied answers stack up?...

a. probe -  too vague to be an appropriate answer.
   Although our device is a probe, a probe could be almost anything,
   including a screwdriver.
   (Reasons to use a resistor and not a screwdriver
      to discharge capacitors:
   * It will not destroy screwdrivers and capacitor terminals.
   * It will not damage the capacitor (due to the current pulse).
   * It will reduce your spouse's stress level in not having to
     hear those scary snaps and crackles.
   From Sci.Electronics.Repair FAQ: Samuel M. Goldwasser's
   'Troubleshooting and Repair of small Switchmode Power Supplies'
   at www.paranoia.com/~filipg/HTML/REPAIR/F_smps.html )

b. multimeter (presumably on Volts range) - not High Voltage rated
   * insufficient test lead insulation (might fry you)
   * will probably fry the meter by flashover or current pulse
   * may damage the monitor by current pulse

c. line analyser - a completely inappropriate 'distractor'
   answer for the totally clueless - this is low-voltage
   _signal_ measuring equipment.

d. high voltage meter - CORRECT!
   * high-voltage insulated
   * resistive probe, typically around 1000 Megohms,
     gives fast discharge without pulse damage.
   * HV meter shows progress of discharge.

(Procedure tip - ground meter (very important!),
probe HV terminal and watch HV reading collapse to zero,
remove probe for 10-30 seconds then re-apply it and
check the voltage.  The EHT may have 'bounced back' due to
'dielectric relaxation' in the reservior capacitor.
Remember that your HV meter has a very coarse scale
so any indication could be a painful voltage!
If there is any reading, leave the probe connected
for a few minutes to totally discharge it.)

c. low voltage meter -  see  answer b. multimeter

There, not so difficult, was it? :-)

Len Warner <[log in to unmask]> WWW Pager http://wwp.mirabilis.com/10120933