HP82160A HP-IL troubleshooting

[J-F Garnier]

(04-04-2020 03:59 PM)MeindertKuipers Wrote:  Did some further digging:
- IL Module sends out multiple frames on startup, and one frame on DIR
- these are picked up by the PIL Box (LED lights), and transmitted back with some delay as expected, I can see this with my scope
- ILPer does not show anything in the Scope screen. Why??
- Frame arrives through the cable at the IL module
- transmission through the receiving transformer is very weak (max 200 mV)

So it looks like the signal is not coming through the transformer. I measure no shorts or broken wires in the transformers, maybe something else is wrong there.

Question is can I replace the transformers by JF's capacitive coupling in the IL module? Or any other way of fixing this?

The frames you don't see are very likely IDY (identify) frames that the 41 is using to check the loop. By default, the PIL-Box just re-transmits these frames to the loop without directing them to ILPer, but you can change that by changing the PilboxIDY setting to 1 in the ilper vil file. You will also have to enable the IDY frame display in the ILPer scope window.

The 200 mV are an indication that the receiver part of the 41 HPIL module is defective, the normal amplitude should be around 1.5V. There may be a short-cut somewhere.
You can't replace the transformers by capacitors, because the transform ratio is around 1:3 to get a 4-5V swing to the digital inputs of the HP-IL chip (the PIL-Box is using analog inputs to directly manage the 1.5V amplitude).

Note also that there are 2 stages of transformer on the HP-IL input. the ESD clamping Zener diodes at the intermediate node. It may be one of these diodes which is dead.

The document "82166C HPIL Interface Kit Technical Guide" (here for instance) gives the general HP-IL schematic on p.10, and is roughly applicable to the HP41 HP-IL module, you will have to trace the tracks to identify the components.

J-F