we're getting a really random trip (August 5 and October 7) which is being caused by a "comm failure" from the "C" core processor on one of our gas turbines. These units are running GE Mark V "dry low NOX" controls. Have checked/replaced boards. triple checked wiring and ribbon connectors. chassis grounds seem to be ok... any ideas?

 

Have you implemented the PROM upgrade procedure recommended in TIL-1480?

Have you checked for the presence of corrosion on the ribbon cables/connectors? A light film of conductive grease (some is usually supplied in the boxes with spare cards purchased from GE) applied to the plastic female end of the ribbon cables will usually help to prevent corrosion. Unseating and re-seating the cables may help to remove any corrosion.

You say the chassis grounds seem okay. What are the DC supply voltage readings with respect to ground? Are they stable or are they fluctuating?

What Diagnostic Alarms are present on the unit?

What error messages are displayed on the LCC/SLCC display of <C> processor and any other control processors when this even occurs?

What cards have you replaced?

The <CD> discrete (contact input and relay/solenoid output) I/O core is connected to the <C> core (TCCA I believe) via a two-conductor, twisted pair (not shielded), <C>'s IONET. Are you certain the IONET cable is firmly seated at both ends and there is no corrosion on the pins/receptacles?

What other alarms (Process- and Diagnostic-) are annunciated at the time of the trip?