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GE MARK VI Fault Code
What do the fault codes FC432 to FC436 "Logic Signal $256L Voting Mismatch" mean.

Hi!

Can anybody help?

We came across fault codes FC432 to FC436 "Logic Signal $256L Voting Mismatch," but could not find any document related to it. From GE 6421 manual we found only fault codes up to #415. The FCs appear on slot9 VCRC together with TRLY J4 fuse 01 (to 06) blown and Coils 05, 01, 03 & 07.

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gbuendia,

Hello,

When did this problem start?

After a trip?

After some kind of loss of 125 VDC?

After a 125 VDC Battery Ground?

After a download from Toolbox?

After a VCRC card was changed?

It's unusual for a Mark VI to annunciate Diagnostic Alarms that are "outside" the window for drop numbers (Fault Codes), but it does happen. In my experience, it usually happens after one or more of the above scenarios happens--and usually after a card is replaced and one or more downloads have been done.

Additionally, what OTHER Diagnostic Alarms are being annunciated by the VCRC?

Is the VCRC a SIMPLEX VCRC, or a TMR VCRC? (In other words, if the VCRC is in slot 15, for example, of <S>, for example, are there also VCRC cards in slots 15 of <R> and <T>, or not? (If there were also VCRC cards in slots 15 of <R> and <T>, then it would be a TMR card. If there were no VCRC cards in slots 15 of <R> and <T> then it would be SIMPLEX card. And, this is all presuming the panel is a TMR Mark VI; if it's not, can you please tell us?)

A voting mismatch indicates that the current value of a signal in one or more processors does not match the current value the same signal in the other processor(s). Sometimes (most often) this occurs because of problem with the card the signal "originates" on, but sometimes, as with outputs (and a TRLY card is a discrete output card) it has to do with a problem with the aux contacts of the relay(s) in question not producing the proper indications (the relay is supposed to be picked up (energized), and the relay aux contacts should be indicating the relay is picked up but they aren't, or vice versa (the contacts are indicating the relay is picked up when it is not supposed to be picked up).

I have also seen similar problems caused by people connecting the 37-pin D-sub cables with power on the circuits. It's VERY EASY for the pins of the male connector to be shorted against the shroud of the female end of the connector when trying plug in the cable when power wasn't properly removed. This can occur at BOTH ends of the cable (in this case, the cables that connect the VCRC card to the TRLY card). the sparks generated when this happens may or may not be visible, so the person trying to re-connect the cables may or may not have seen them to know of the problem. But, it can cause problems with both the I/O card (the one in the processor rack, the VCRC in this case) and/or the I/O terminal board (the TRLY in this case).

You also mentioned problems with fuses.... Are the relays you mentioned actually assigned (used) in the application, or are they spares (unassigned)?

LOTS of questions, I know--but most of them are intended to prompt some thought and investigation. Yes; it would be very helpful if you would provide the answer to ALL the questions (even if they don't seem relevant), but please do provide write back on what you find as you resolve the issue!

Hope this helps!!!

CSA

Thanks for the reply. We are still actually puzzled with the event that is why we are analyzing it (internally). The GT was re-started successfully but we are not confident that it would not happen.

>When did this problem start?
The alarms came before the TRIP initiated by

>After some kind of loss of 125 VDC?
There are no evidence of any loss on any of the redundant power supply? Besides there is no recorded power dip or loss in any of the cards or from PDM module.

>After a 125 VDC Battery Ground?
There is no evidence of any ground fault.

>After a download from Toolbox?
I'm not familiar with the "toolbox" but the alarms are DALMLOG provided by GE services

>After a VCRC card was changed?
There are no recent card replacement.

>Additionally, what OTHER Diagnostic Alarms are being
>annunciated by the VCRC?
I can provide you with the list of alarms.

>Is the VCRC a SIMPLEX VCRC, or a TMR VCRC?
We have TMR VCRC.

>You also mentioned problems with fuses.... Are the relays
>you mentioned actually assigned (used) in the application,
>or are they spares (unassigned)?

Fuse blown indication occurs on TRLY output cards with assigned and unassigned outputs. One of the load is solenoid each for Slot 9 and Slot12 output cards, provided with the respective jumper connection. Since there are no indication of actual voltage drop and the TRLY has a fuse blown monitoring to activate at <14V, is there any likelihood of card malfunction.

buen dia, gbuendia,

Here is what is posted from your reply:

>When did this problem start?
The alarms came before the TRIP initiated by

There is nothing after "....before the TRIP initiated by"

And you mentioned re-starting the unit and being unsure about ... something.

What caused the trip, please?

Dear CSA,

Thanks for your interest.

The Slot9 TRLY J4 card alarms are:
1. Relay Output Coil 05, 01, 07 and 03 does not match requested state
2. Fuse 01 to 06 are blown - but all are ok when checked
3. FC432 to FC436 Logic Signal Voting Mismatch - our original query.

The Slot12 TRLY J4 card alarms are:
1. Fuse 01 to 06 are blown - but all are ok when checked

We believed the trip was initiated when Coil07 Unit Lockout Master Permissive (4X-4), loses its status and return to failsafe state.

We have redundant power source, and since we do not have any evidence of voltage drop or any earth fault alarm for the matter, the system was reset and restarted without any issue. However, what is the likelihood that the issue was caused by a TRLY output card malfunction? Have you encountered this type of problem before?

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gbuendia,

I'm not sure I understand 4X-4.

I have seen unusual occurrences like this when there are power supply issues. For example, you have mentioned having redundant power sources, and I presume (because you haven't provided any information) you are referring to a 125 VDC battery AND a GE AC-to-DC conversion module (typically called a DACA). OR, if the unit is a steam turbine control panel it may possibly have two DACAs as the main power sources.

In any case, DACAs are well-known for causing problems. They are NOT filters by any stretch of the imagination, and if the input power to the DACA dips or spikes the DACA can actually amplify the dip or spike in the 125 VDC output. They really only work well when the AC power input to the DACA is clean and well-regulated. When it's not--the results can be very bad--including failed processor rack power supplies.

Another effect of poor input power to DACA(s) is intermittent problems such as the one you described where unusual Diagnostic Alarms are annunciated.

Also, there are several versions of TRLY I/O terminal boards used in Mark VI turbine control panels. It is very important that the proper version be identified in Toolbox in order for the proper diagnostic functions be enabled, and improper diagnostic functions are disabled. Have a look in GEH-6421 at the several versions of TRLY which may be used in a Mark VI panel, and verify that the card associated with the unusual Diagnostic Alarms is properly specified in Toolbox for the VCRC card(s) it is associated with.

Lastly, as written the function of the 4X-4 relay output is not clear. If it is driving a large coil with a high inductance that has been known to cause similar problems, also. The description indicates it might change state when the turbine is tripped--when lots of other relays and solenoids also get de-energized or energized. And, this can affect the 125 VDC power (battery power is usually pretty robust, but not always, and DACA output power can be more susceptible to spikes and dips caused by solenoid switching.

Anyway, it seems for the time being there is no problem. Thanks for the feedback.