HP82160A HP-IL troubleshooting

[J-F Garnier]

(04-05-2020 10:53 AM)MeindertKuipers Wrote:  Is it safe to test the IL loop without the zeners? I am a bit uncomfortable with this analog stuff ...

Usually, ICs include built-in protection (diodes to GND and VCC) to clamp any small power transient voltage. However, for the HP-IL IC, the protection is reduced on the HP-IL receive pins.
From the IC spec:
"Since the normal input voltage of the HP-IL receive inputs may rise above VDD, only the diode to ground is used on RXD0 and RXD1."

So the protection is made by these external 6.2V diodes. I advise to replace these diodes, more usual 5.6V diodes (like BZX55 or 85 5V6) may work too.

J-F

Added:
I may explain why I remember this particularity of the HP-IL chip: at the time when I was working on HP-IL I had to develop new applications and replace the HP82166 kit with the HP-IL chip and our own microcontroller firmware. So we asked HP to provide us just the 1LB3 chip and the pulse transformer; and I remember that someone (from HP?) explicitly warned us about the ESD sensitivity of the 1LB3 on these pins. We used to take ESD precautions (that we usually didn't take for standard ICs) when manipulating the HP-IL chip.