Quantum problems

[OZEE]

In one of our plants we are having problems with a particular rack "dropping out" in a Modicon quantum system. Forgive me if I use some incorrect terms for the Modicon stuff -- I'm an AB-guy and it's been many years since I've worked with Modicon. The PLC is a Quantum 534. There are three racks connected via 140CRP93200's. The problem is rack 3 in a 4-rack system. Reportedly, one of the racks is dropping out -- dead... Prior to my visit to the plant, they had checked all connections, cables. Had their local SqD-guy come out to help. All have had no significant improvement. They have replaced power supplies, comm modules, cables... When I got to the plant Thursday, I found that the terminating resistors on the RIO were not in place. So I ordered them and drop-cables, then installed them over the weekend, while the plant was down for maintenance (actually, while I had to shut them down to do another project....) Yesterday, they started the plant back up. That system had run for less than an hour and the rack faulted again. They came and got me. Quick inspection showed no apparent comm-problems. So it appears that the problems come, then go away just as quickly. Things I've checked: 1) Terminating resistors on RIO. Installed missing resistors. 2) Drop cables are all > 10', professionally made. 3) Unit temperatures all appear to be within reason. Most feel just slightly warmer than skin-temp. Nothing feels too hot or too cold... 4) All racks appear to be properly grounded. 5) All power supplies have the correct jumper set for 120-VAC. Any hints for anything else to check?? I'm becoming suspicious of power problems, but am desperately needing further guidance! Thanks!

[rammin48]

I had an issue some years ago that was similar. It was the rack itself. This particular unit was subjected to large temperature range. It was in a building that was heated but if the fans kicked on the room would drop to the outside temp in very short order. Replaced the rack and the problem went away.

[Crossbow]

If you've already tried the modules and cables, I would also look at that rack. There are eletronics on the backplane unit that may have gone bad or be a loose solder connection.

[Camel]

I know it's a little late but..... If there are any analog cards in that rack, check for a shorted loop. I konw it sounds strange but I had about a weeks worth of trouble with a 140CPU534 14 because of it. It would run fine for a while, then poof, nothing. The analog cards were in the cpu rack. I couldn't even connect to the cpu.