SLC 5/05 Ethernet Flicker

The Setup
In my plant I have about 20 SLC5/05 on an ethernet network. This network has been functioning pretty well for about 10 or 11 years. Coming out of the processors ethernet RJ45 connection is a short piece (1.5 too 2 feet) length of cat 5 cable with RJ45 connectors on both sides. This short patch cord is connected to a media converter (over the years the type and manufacture of the converters have changed due to necessity.) that then goes to Fiber optic cable using ST type connectors. The Fiber optic then handles the network comms from that point forward.
The Issue
Over the years when I would see a processor either off the network or start to drop off come back again and again 99% or more of the time it was the media converter. Swapping it out usually would take care of the problem.
However lately some simple media converter swaps does not stop the network flicking.
As an example this morning I had a processor dropping of and reconnection to the network. I saw this both on my Plant Scada package and also on RS Logix 500 using Linx Gateway on the same PC as RS logix. When I checked the media converter I saw that is was an older model and replaced with a
Trend net model #TFC-110MST H/W: D3.1R (manufacture info Here )
With no change in the network flicker
The Chase
The IT people I work with can at times be a bit difficult. I am hoping that the members of the forum can perhaps point me in some directions to take while trying to work through this issue. As always I truly appreciate the support and guidance I get as a member of this forum. As I like to say you don't need to know all the answers just where to be able to get the answers and PLCS.net is a great resource.
Thanks for the Help
Michael

on an old existing system I would terminate new cat 5 ends, and in your case get a communication company to come in and polish the fibre optic ends, there is a good chance that due to age the ends themself need polishing. Ideally the company you bring in has a data tester and can check the overall attenuation

The first thing I would do is make sure that the Ethernet port of the SLC-5/05 has a Diagnostic File configured for it. That's going to give you some information from the SLC's perspective on network conditions.

SLC-5/05 controllers prior to Series C hardware have a 10 Mb/s half-duplex 802.3 Ethernet port only. 90% of the time, they work correctly when connected to an Auto-Negotiating switch port because link speed sensing will succeed and duplux negotiation will fail and the switch will default to half-duplex. Check the switch Duplex state very carefully.

If you can configure the switch for 10 Mb/s Half-Duplex, that will work 100% of the time with these older SLC-5/05 controllers.

If the controller has the Series C hardware with a 10/100 Mb/S Auto-Negotiating Ethernet port, it will state so on the label on the side of the controller and have a green label on the front stating that it's a 10/100 Mb/s port. These can be connected to an Auto-Negotiating switch 100% of the time.

Your next step will be to get some diagnostic information from the fiber optic port of the switch that your media converter connects to over fiber. This may require some co-operation from your IT department, or it may be simple enough to poke at with tools like a Web Browser or TELNET session. What make and model of switch do the fibers from those TrendNet converters go to ?