Mark V - Simplex - TCDA change state continously


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Dear All Mark V expert,

Currently we have trouble with our mark V system. We have Mark V simplex. Turbine trip because TCDA card core <R> reset with diagnostic alarm ID OBJ #4 reset. All input go to alarm state. From DCC/LCC LCD found that after unit trip TCDA state change continously from A2 to A7.

We have checked JP voltage (supply from TCPS) and not found any problem. Checking result for IONET voltage for cable connection integrity also found no problem.

We have replace TCDA core <R> and TCPS core <R> with our spare but the problem not solve yet.

Jumper setting for IONET termination resistor are IN for TCEA and TCDA.

We have check AC ripple at DTBA and DTBB and found the AC voltage varies from 2 - 9 Vac.

Any help appreciated...
The IONET should "loop through" all three TCEA cards and terminate on the TCDA card. In other words, the IONET should be connected first to the TCEA card in Loc. 1 (<X>), then to the TCEA in Loc. 3 (<Y>), and then to the TCEA in Loc. 5 (<Z>), then to the TCDA in Loc. 1 of <QD>. So, if the IONET termination resistors are in the IN position on the TCEA cards, they are in the wrong position.

I believe you can refer to the Mark V Application Manual for information on the IONET termination resistors and how they should be terminated for SIMPLEX and TMR applications.

AC ripple at levels above approximately 40 VAC can cause this kind of problem, also. As can spikes from the DC battery charger, or from the de-energizing of "large" unsuppressed DC coils, such as 20CB-1, 20FD-1, and older GXA relays, such as were commonly used for 52GX-1 relays and other functions.

I believe there have been other threads on about the components used for RC "suppressors" across DC coils to help with reducing the effects of voltage spikes caused by large DC coils when they are de-energized. Use the 'Search' feature of to search for them.