The electrode, as you know, needs to be quite close to the burner. 3/16 inch or so. The burner itself needs to be well grounded for the spark to happen. Check with your multimeter to see that the burner is well grounded. If there is a lot of rust or loose connections, that could be the cause. If grounding is questionable you can route a ground wire there and see if the spark will jump to it.
Does the gas valve open and emit gass for a few seconds when you first turn it on? If so, then you should be able to light by match just to see if that part of the control board is functioning.
