Controllogix 1756-L55 Solid Red OK LED

I bought a used L55M23 processor on Ebay and turns out that it doesn't work. RSLinx can't find it whether by RS232 or Ethernet adapter.
With this solid red OK LED, is there anything I can try before throwing it away?

Welcome to the PLCTalk forum community !

Unfortunately, a solid red OK light indicates the controller has failed a low-level self-diagnostic and the operating system is not even starting.

• Remove the RAM back up battery.
  
• Give the controller a few firm raps on the table.
  
• Blow the controller out with compressed air.
  
• Disassemble the memory daughtercard from the CPU.
  
• Give it a good bath with isopropyl alcohol and let it dry.
  
• Inspect the backplane pins.
  
• Put the controller in a freezer for a couple of hours.

If those don't at least get you to a flashing red OK LED, then see what your recourse is with the eBay seller, or promote the controller to dust cap duty.

Ken Roach said:

Welcome to the PLCTalk forum community !

Unfortunately, a solid red OK light indicates the controller has failed a low-level self-diagnostic and the operating system is not even starting.

• Remove the RAM back up battery.
  
• Give the controller a few firm raps on the table.
  
• Blow the controller out with compressed air.
  
• Disassemble the memory daughtercard from the CPU.
  
• Give it a good bath with isopropyl alcohol and let it dry.
  
• Inspect the backplane pins.
  
• Put the controller in a freezer for a couple of hours.

If those don't at least get you to a flashing red OK LED, then see what your recourse is with the eBay seller, or promote the controller to dust cap duty.

Click to expand...

Thanks Ken, it is in the fridge now but I won't hold my breath. The boards are super clean and the backplane pins are intact. I also tried to take the memory board off. It doesn't come with a battery but I think it isn't an issue, i tied to give it a 3.0 VDC to the battery pin but it doesn't help obviously.

BTW, do you know what does the board in the picture below do? It sticks to the mainboard by a bead of hot glue which made me think it might have sth to do with this error...

FWIW, eBay is extremely buyer-friendly, at least in the USA. You can request refund or chargeback even if you don't have a legit reason. You should be able to get your $ back assuming you didn't wait too long.

Send it back and buy another.
(unless the listing said it was fu**ed)