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Old June 15th, 2018, 02:45 PM   #1
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glenncooper is offline
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1734 Modules Failing - Destroyed

Hello. I've been working through a problem at one of my customer sites where a section of 1734 I/O is getting destroyed. Excuse the long explanation, but the situation takes a bit of description. We have five production lines that are built heavily on the 1734 I/O via DeviceNet. The lines are about 10 years old, and in general we get great performance from the Point I/O along with the expected occasional module failure. In the last month we've had two lines create multiple failures in exactly the same way on their respective identical I/O racks. Each rack contains 20 I/O cards - mostly a mix of IB4, OB4, ITI, OE2V, IE2V, etc. Because of the I/O count we have a 1734-EP24DC. And 6 modules from the that we have a 1734-FPD that allows me to have some 5 volt stuff. All of the modules that fail are failing between these two power distributors. We get one random module that fails and is destroyed (Module Status goes red). Then at some point we'll get another module that fails, and these keeps going. In every case the modules are electrically destroyed. I spent several days carefully analyzing the first line, looking for thermal issues, contamination, errant electrical surges, etc. I inspected the failed modules under a microscope to see if there was any sign of obvious electrical damage - none. I discovered an issue with one of the wiring bases not reliably sending one of the network signals down the bus. At the end of the day I replaced the EP24DC, the FPD, all of the terminal bases, and all of the I/O modules. That line has been okay for a month now. We've started seeing this identical sequence of failure on another line. I would really like to understand how a sequence of destructive failure like this can occur. If anyone has ideas or similar experiences I'd love to hear about them - Thanks much!!
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Old June 15th, 2018, 04:31 PM   #2
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harryting is offline
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Never had this happen to me, however, I do not use PointIO for mission critical stuff ever since I had two new AI module malfunction straight out the box.
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Old June 15th, 2018, 04:51 PM   #3
Ken Roach
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I can't diagnose your system, but I'll tell you that overvoltage on the logic bus supply has caused similar results in 1734-ADN and 1734-PDN based systems I've troubleshot in the past.

On those systems they had some power supplies that failed and put over 50 volts onto the input of the 1734-PDN. While I/O is very well isolated from the logic bus, I think the bulk power supply is only limited and tested up to about 30 V. An intermittent short to 120V will definitely do the job too.

The report that one of the terminal bases wasn't reliably connecting the logic bus suggests that the modules are getting intermittent logic power; I've killed a 1734-AENT (a more complex module, sure) with a loose wire that caused rapid intermittent power disconnection.
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Old June 15th, 2018, 10:52 PM   #4
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seth350 is offline
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We have the same issues except using 1734-AENT. Our rack consists of analog in/out, thermocouple modules and 120V outputs. We have had bases electrically burned, modules burned, modules that just quit working ( namely thermocouples), and bus controllers that just quit communicating.

When I first started digging into the issue, I found the bus was under supplied. There is a program from Rockwell that allows you to build a Point IO rack. The software will then recommend if you need to add EPACs or EP24DC modules in the rack and where. The rack we had was short two EP24DC modules. I installed them according to the software recommendations but we still have issues.

One thing I have learned is that the module bases are highly susceptible to moisture, dirt, and corrosion. The pins are not soldered to the board, they are just spring pins.
They do not like heat either.
“Did the Lord say that machines outta take the place of livin’, and what’s the substitute for bread and beans? Do engines get rewarded for their steam?” -John Henry
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