HP82160A HP-IL troubleshooting

[MeindertKuipers]

Somewhere deep in my drawer I have en HP-IL module for the HP41 that I wanted to test. It now consistently shows transmit errors, even with no equipment connected (loop closed). Cables are OK and not broken, Beyond this I am a bit outside my comfort zone. Any tips in the next steps troubleshouting? Does it make sense to connect a scope to the IL signals?

Hope someone can help,

[KeithB]

How do you know the cables aren't broken? Did you check for beep? i.e., ohm them out?

[MeindertKuipers]

(04-02-2020 01:59 PM)KeithB Wrote:  How do you know the cables aren't broken? Did you check for beep? i.e., ohm them out?

Yeah, sure I did. Some extra info: when I connect my PilBox, the led comes up briefly when doing a DIR, and then Transmission Error

[MeindertKuipers]

(04-02-2020 01:59 PM)KeithB Wrote:  How do you know the cables aren't broken? Did you check for beep? i.e., ohm them out?

Yeah, sure I did. Some extra info: when I connect my PilBox, the led comes up briefly when doing a DIR, and then Transmission Error, so somethiong is happening. Maybe the send works good, and the receive on the HP41 side is broken?

[J-F Garnier]

(04-02-2020 02:28 PM)MeindertKuipers Wrote:  

(04-02-2020 01:59 PM)KeithB Wrote:  How do you know the cables aren't broken? Did you check for beep? i.e., ohm them out?

Yeah, sure I did. Some extra info: when I connect my PilBox, the led comes up briefly when doing a DIR, and then Transmission Error

Ha, that's interesting, the HP-IL is alive !
You may try ILPer and enable the scope mode in it to see the HP-IL traffic.

There is also an obscure cause of constant 'Transmit Error' on the HP41: check flag 33, if set the HP-IL ROM will refuse any HP-IL operation and give this error.

J-F

[MeindertKuipers]

(04-02-2020 05:12 PM)J-F Garnier Wrote:  

(04-02-2020 02:28 PM)MeindertKuipers Wrote:  Yeah, sure I did. Some extra info: when I connect my PilBox, the led comes up briefly when doing a DIR, and then Transmission Error

Ha, that's interesting, the HP-IL is alive !
You may try ILPer and enable the scope mode in it to see the HP-IL traffic.

There is also an obscure cause of constant 'Transmit Error' on the HP41: check flag 33, if set the HP-IL ROM will refuse any HP-IL operation and give this error.

J-F

Thanks for stepping in JF. Although the led in the PILBox lights briefly, the scope window stays empty, and I always see the Transmit Err. Same on another 41C

[J-F Garnier]

(04-02-2020 05:26 PM)MeindertKuipers Wrote:  Although the led in the PILBox lights briefly, the scope window stays empty, and I always see the Transmit Err. Same on another 41C

When you turn the HP-41 on (with HP-IL plugged in), is there an unusual delay of a few seconds? This happens when the loop is broken.

J-F

[MeindertKuipers]

(04-03-2020 08:50 AM)J-F Garnier Wrote:  

(04-02-2020 05:26 PM)MeindertKuipers Wrote:  Although the led in the PILBox lights briefly, the scope window stays empty, and I always see the Transmit Err. Same on another 41C

When you turn the HP-41 on (with HP-IL plugged in), is there an unusual delay of a few seconds? This happens when the loop is broken.

J-F

It takes about one second for the display to show, the same with the cables connected to each other or when both IL cables are loose. When I press ON on the HP41 the LED on the PIL Box lights up, a bit less then one second, and then the display comes on. The scope window in ILPer stays empty ...
Movies of the events in my Dropbox at https://www.dropbox.com/sh/tsuiuskmln00l...tDaKa?dl=0

I suspect a hardware issue so I will take out my scope and start digging in the HP-IL interface

[MeindertKuipers]

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?

[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

[MeindertKuipers]

Thanks JF,

Then its is probably the zeners in the input circuit. When I test them with a DMM in-circuit I get a beep in both directions for both zeners, but in this case I am also measuring through the transformer which has a very low DC resistance. Next is to remove the zeners and test them off circuit.

Is it safe to test the IL loop without the zeners? I am a bit uncomfortable with this analog stuff ...

[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.

[MeindertKuipers]

So I have now removed the zeners in the input circuit, and they appear in good working order with my tester. I have ordered a few new ones and will test these in the IL circuit as a next step, but after that I am a bit at a loss. It could still be posssible that there is something wrong with the transformers, but I have little chance of getting a replacement for these.

I am open to any further ideas to get my HP-IL module fixed ...

[MeindertKuipers]

Good news!

I remembered I had a cheapo component tester, which could also test inductance. And this gave really strange results on the secondary output transformer. So I checked (again) for wires, and actually did find one of the transformer wires broken. It was just long enough to solder to the pin (see picture, taken through magnifier glasses with my phone). And it now works!

Thanks JF for your support, I learned a lot!