In 6FA MARK V diagnostic alarm

1.TCQA 4-20mA outpt disagrees w/ref CH.A (Alarm persisting) in <S> core
ST:1 DROP: 1250

ST: 0* DROP:1342 (alarm some times only and not holding)

Please let me know what could be the reasons for this alarms and need clarity about the wiring from SRV LVDT to all core.

The best clarity you're going to get is to RTFM (Read The Fine Manual). In this case Section 7 (I believe) of the Mark V Application Manual, GEH-5980. There are very good drawings of servo-valve outputs and LVDT feedback. Basically, there are two (2) LVDT feedback signals for each device equipped with LVDTs, and both of those signals are sent to rack of <R>, <S> & <T>, which then choose the higher of the two signals to be "the" device's LVDT feedback signal.

When the two signals differ by an excessive amount, the Diagnostic Alarms you describe will be annunciated. The SRV is usually assigned to either the first or seventh servo-valve output.

You need to determine which device is assigned to the seventhth servo-valve output (sounds like it might be a SRV) and look at the two feedback signals of that device to determine the difference between the two and resolve the problem. Because the two feedback signals should be very close to each other.
The difference between the calculated positions of the LVDTs is greater than 5%. This alarm applies only to regulators using more than one LVDT.

I would pull up the diagnostic counter page (see GEH-5980 4-3.1.for running diagnostic counter on <I>) compare the associated LVDT values for differences. Check each processor, we have had the LVDT's all match on R & S but not on T.

The most common issues I have had to come behind and fix
1. Poor connections at terminals and crimps
2. The bolt/rod end connector wearing loose causing the rod to bounce around during operation.
3. Low quality LVDT calibration.

Less common issue I have experienced are card issues/failures. May have been corrected by simply resetting the card connections, but if we shutdown because of a Mark V issue, we're replacing card(s) and shipping them off for testing/repair. (I do not keep track if board with suspected problem had issues or not.)

So far I have only had to replace one LVDT because it failed.

CSA is referring to GEH-6195 not the GEH-5980, right section, right title, wrong manual #.

Please let us know what you find.