Try a search at www.zetex.com (Zetex is a semiconductor manufacturer, many part number starting with Z)

Hi, I may suggest you to find out how this zener diode is connected, if as a reference voltage, or as a overvoltage shortcircuit protector, (the second if the Z pin goes to the o/p voltage, and the back of the arrow goes to ground).

Hi electricuwe & algarin,

Hi Electricuwe, I  tried the Zetex homepage, and they listed down about 15 list of components all bearing the same number ie FK 330. I have asked them what FK 330 means and am awaiting their reply By the way there is also a manfacturer's marking on the chip, letter M, this is definitely not Motorola as the two legs of the letter M appears to curve inwards. Who could this manufacturer be?

Hi Algarin, The chip do not have any polarity marking, but on the PWB component side, it is marked as VR. The chip is connected in parallel after the 24VDC supply  and inductor.
Dimension of the chip is 8mm X 6mm X 3mm height and the leads are "J" bend for surface mounting.

If the supply is DC and not AC then the diode is probably
in case the power supply is accidentally wired backwards. This would blow a fuse. If it is in parallel with a xformer(AC supply) secondary then it is a half wave rectifier. I cant help identify the logo you described but may be matsushita? I would thumb through a digikey magazine or similar and look for that particular logo. Good Luck

Hi Buzzup and Algarin  and Electricuwe,

I managed to get the supplier for this ZNR component. THe
supplier is Matushita, and this is basically a Zinc Varistor
( that's why it is abbreviatedZNR). The PLC is now kicking alive, Thanks to all who have responded esp Buzzup.
Joy to you.
Chandra