[volt-nuts] GPIB Issue with 3458A

Todd Micallef tmicallef at gmail.com
Sun Dec 31 09:09:23 EST 2017


I put together a quick script for testing your connection. I have emailed
it to you but attached it here for others if needed. It will be easier than
running the other program.


On Sun, Dec 31, 2017 at 9:00 AM, Dr. Frank <frank.stellmach at freenet.de>

> Randy,
> I doubt, that your hp unit is defective, as it might work under certain
> circumstances, and also the FW version 8.2 vs. 9.2 will not make any
> difference, as only a few pair of bytes are different. All versions of the
> A5 board are designed to be completely interchangeable over all versions of
> 3458A instruments.
> I have another theory, which deals with the hardware version difference
> between the agilent and the hp unit.
> Your agilent unit might already have the 66547, full SMD board for A5,
> whereas the hp will for sure have one of the old 66505/515, through- hole
> boards, Rev A, B, or C. Illya has all of them pictured in his first 3458A
> repair blog.
> All the  old versions (A, B, C) have GPIB bus transceivers, TI 75ALS160
> for the data bus, and NS 75161 for the handshake signals.
> The new SMD board has TI 75ALS160 / TI 75ALS161, instead.
> So, the handshake bus uses a different logic family for the new board, and
> therefore, the logic levels / immunity might be slightly different.
> My hp3458A has got the REV C A5 board, and it's from 2000.
> Since 2009, I run a similar datalogging program for capturing LTZ1000
> output versus time, each 4 seconds, on an old PC with WIN98, Turbo Pascal,
> an XT bus GPIB card from CEC, with the NEC chip.
> This program and hardware ran properly for years, (decades), until more
> and more errors during the 24h acquisition runs occured, vaguely reminding
> me of your trouble.
> The output values were always correct, but frequently, 10sec time-outs
> ocurred, giving zero readings in the datalog. This time-out is obviously
> related to the handshaking mechanism.
> Finally, I found out, that the old ATX PSU was failing, especially its
> input snubber network was gone defect, which probably created big EMC
> spikes.
> After replacing the PSU, all these errors vanished completely.
> My conclusion was, that the GPIB bus is susceptible to such EMC
> disturbances, although it's solid TTL logic.
> As obviously the handshake signals were affected only, their higher
> susceptibility to disturbances may be caused by the difference in the logic
> family of the transceiver IC. The agilent 3458A might be more tolerant to
> that, having the ALS161 version, instead.
> So you might also look for EMC problems in your lab, like SMPS, LED lamps,
> or a defective PC power supply.
> Maybe, these Prologix adaptors (clones?) have critical logic levels,
> especially on the handshake bus, or an improper ground.
> You might search for these signal problems directly on the GPIB cable.
> Frank
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