Hi All,
For those who read my previous post about burning PIC16F84A chips. I was working on a very simple circuit, driving two leds in series with 470 ohm resistors and I managed to blow another chip. Obviously, I suspected the lab power supply. I put the oscilloscope on its output and the voltage was perfect, no ripple, no noise, no anything. But in the moment I decided to turn it on and off, I noticed some very short spikes of voltage that get toward 30V, if not more (I actually suspect they get up to the maximum voltage of the transformer which is close to 40V). I was trying to be a "good boy" and to protect the chips by turning the power supply on and off while inserting/removing the IC in circuit and this was actually what was destroying them... It cost me a couple of microcontrollers to discover my lab power supply has a transient fault, but at least there are no more mysteries... I used this lab power supply very often for a few years, with other boards with Zilog microcontrollers, but I ignored the fact those boards had their own regulator on board and this is why none of them blew up... Thanks to all who helped me with ideas/suggestions.
Regards, Nicolae