On Mon, 26 Aug 2013 15:17:35 +0100 "Arfa Daily"
wrote in Message id: :

The internal meter battery often does not source enough
voltage to bias the diode 'on' sufficiently to obtain any meaningful
reading. If the meter has a 'diode test' setting, this most certainly will
not. The reason that these high voltage diodes behave like this, is because
internally, they are many ordinary diodes stacked in series to get the high
PIV rating. Think 10 x 1N4007 in series, which would give you a diode with a
PIV rating of around 10 kV, but with a forward voltage drop of 6 or 7 volts.

That's true of most DMMs, but there are exceptions. My Keithley 2000 will
bias a diode up to 10VDC. Useful for checking smaller zeners as well.