I have bizarre problem to make work 16F628-20/P @20MHz.
I was probe with cap =10pF to 27pF + XTAL 20 and 4 MHz , and also to config internal 4MHz osc but it don't want work.
When I program it and clear all is ok.Verificate of HEX is to OK 100%.
In that PCB board I was probe 16F628-04/P and also 16F84A at 4 and 20 MHz and that two work 100% OK.
Is possible to a NEW pcs of 16F628-20/P want to program flash mem but don't want work ?

Regards Robert