GPIB conflict between instruments

[Antonio_lara]

Hello, I am facing the following problem: I am trying to control several devices through GPIB with the same computer, all the devices connected to the same GPIB card. One of the devices (EG&G 7265 lock-in amplifier) sends strange symbols back to the computer when some query is sent (and the utility that came with the GPIB card shows its name also with strange symbols), only when another device (Agilent ENA network analyzer) is also connected to the rest of the instruments (even when the network analyzer is off!!!). Just by unplugging the GPIB cable from the analyzer, the lock-in sends characters fine again, and its name shows correctly. Of course they have different GPIB addresses.
Does anyone know what can be happening?
The network analyzer works always fine, regardless of whether the lock-in is connected to the rest of devices. The remaining devices don't interfere with any of the former.
Thank you for your time.

[crossrulz]

The only time I've seen anything like that is when two instruments had the same address.  You already said that those two instruments have different GPIB addressed.  You might want to check to make sure there aren't any conflicts with other instruments.

I've also seen weird things when the total GPIB cable length gets too long, but that's usually a double character.

[Antonio_lara]

Thank you for answering. I know, it is a strange problem, I attach a screenshot of what happens. It's strange, the cables are not that many, and as far as I know, there were no conflicts with other devices...

[nyc_(is_out_of_here)]

try a different GPIB cable?

[Antonio_lara]

Thanks for the suggestion. I exchanged all the cables I currently have with each other and the same thing happens every time. I will try to borrow another cable, but each device works fine individually, except when connecting the cables of these two devices at the same time...

Maybe the GPIB connection of the network analyzer is making some kind of short circuit? Because the error happens with the analyzer on and off, just when plugging the GPIB cable. I will check the pins, to see if there is something strange. Perhaps some problem with the ground pins? Let me check it.

[Albert.Geven]

A known problem is cable length and handshake speed.

Older instruments need a slower handshake, Try 1 microsecond busspeed in your GPIB setup!