PICkit 4 (and ICD4) have a bug in high voltage program (Vpp=12V) mode which affects many older PICs like the 16f84(a). Workaround is to put a 100 ohm in series with the Vpp/MCLR line. See www.microchip.com/forums/tm.aspx?m=1082740&mpage=4
I found the circuit on the internet, but I can't find the site now. It was a Japanese site I think. I changed one component value, the zener diode, from 12V to 13V and had a bit more success. Well, maybe, it was all a bit strange as I was blowing devices up using the Microchip programmers. I'll try to find the site.
Found it, it's here: kurikou.sakura.ne.jp/pokekon/option/picdrive.html It says no commercial use and no reproduction of the circuit digram. I redrew it in Kicad though, so that's maybe different.
PICkit 4 (and ICD4) have a bug in high voltage program (Vpp=12V) mode which affects many older PICs like the 16f84(a). Workaround is to put a 100 ohm in series with the Vpp/MCLR line. See www.microchip.com/forums/tm.aspx?m=1082740&mpage=4
That's very interesting, thanks for the link. I'll add the resistor next time I'm programming one of those older parts.
Do you have a schematic for the programmer?
I do have one, I'll make the github repository public.
I found the circuit on the internet, but I can't find the site now. It was a Japanese site I think. I changed one component value, the zener diode, from 12V to 13V and had a bit more success. Well, maybe, it was all a bit strange as I was blowing devices up using the Microchip programmers. I'll try to find the site.
Found it, it's here: kurikou.sakura.ne.jp/pokekon/option/picdrive.html
It says no commercial use and no reproduction of the circuit digram. I redrew it in Kicad though, so that's maybe different.