K8026 dimmer problem

I have built this 3.5amp dimmer -I thought without problem and it looks just like the photograph in the instructions. However on testing with a 150watt lampbulb it fires up fine at 100% brightness and on rotation of the potentiometer the light begins to dim as expected. This implies that the trigger circuit is firing the diac correctly initially. However after about one sixth of a rotation of the pot, it doesn’t dim any further but does remain lit! The AC current at full brightness is 0.623amp and falls to 0.5amp but doesn’t reduce any further.
Anyone got any advice as to what the problem is and how to correct?

We are confused:
Normally, when the pot is turned fully CCW, the bulb should be off. Is this the case?
Next, when you turn it CW, it should light from 0 to 100% when turned fully CW.

Hi Vel 417 you are correct - my fault - I started the description from the potentiometer being at the fully CW turned ‘on’ direction. If you start with it in the fully dimmed/off CCW position, the light comes on immediately but only slightly dimmed (about 80% of full brightness)! Rotating the pot CW takes it up to full brightness 100%. I just can’t get it to dim more than 80%. But the fact that I can partially dim/brighten the lamp by rotating the pot in the correct direction must mean that the trigger, diac and triac components are mostly good.

Be sure that R5 is NOT mounted (only for US 110V AC)

Hi VEL456, this kit only has two resistors and the potentiometer to create the trigger delay. It is designed for both 240 and 120V AC.

VEL456 meant R2, not R5.
This is correct, if your input voltage is 230VAC, should not be mounted.
(See page 6 of the manual).

really stupid mistake I can see the @ 120V sign now. This will solve the problem.