Mark V 96FG-6 Transmitter Issues on S Core


Thread Starter


I am having issues with a TMR MARK V control system on a GE 7EA Simple Cycle Gas Turbine. I have exhausted my knowledge and troubleshooting abilities and need some further guidance. Below is the issue as well as the steps I have taken to troubleshoot it.

<b>Control System:</b> TMR MarkV. Installed in 2001. <RST>, <C>, <CD>, <PD>, <P>, <QD1>, <QD2>. All updates as far as PROM upgrades and TILS have been addressed to the best of my knowledge and past maintenance logs. On <S> Core, TBQC JBS ribbon cable connects to TCQF (NOT TCQA) JB ribbon cable input.

<b>Issue:</b> 96FG-6 is giving us false readings. <R> and <T> are reading around -5 and <S> is reading about -74 when turbine is not running.

<b>Back Story:</b> During a run in March, we noticed alarms that appeared on the screen as we ramped up. Voter mismatch alarms and Trans Manifold Pressure Xmitter Trouble. After further investigation, we noticed this issued appeared after calibrations on the gas pressure transmitters in the gas house and the recalibration of our gas valves servos. As mentioned, when we are not running, <R><T> hang around -5 and <S> hangs around -74. During a run, <R><T> will be about 12-15 psi lower than our other 3 7EA turbines at the same load. <S> will be work itself to about -50 - -40.

1. Tried recalibrating 96FG-6. It was still 4mA (on meter) at 0 pressure and 20mA (on meter) at 400 PSI.

2. Traced voltage back from each Junction Box back to the Mark V. At the transmitter wire terminal block, it read 23.95 VDC. At the Mark V, it read about 24.15 VDC.

3. Checked mA readings in the same fashion, 4mA at all locations.

4. Replaced TBQC on <S> core after I noticed a tiny hole on top of the foil (burden) resister. The other board produced the same outcome.

5. With the old TBQC board out, I used a meter to check the resistor on MAI06 and it read 100 OHM.

6. Since the new board caused an issue on MAI07 and did not fix the issue on MAI06, we put the old board back in.

7. I replaced the BJ jumper on MAI06 with a "new" one, did not fix.

8. Tested the JBS to JB ribbon cable, all 40 pins, they all have continuity and read .3 - .4 OHM.

9. I tried investigating the voltage issue through Diagnostic Counters HMI tool, for some reason, I cannot view TCQF information, only TCQA. Since this input is connected to TCQF, that is a let down. However, on <S> Core, 24V reads around around 27.4 VDC, other cores are mid 26 VDC.

10. We took the input for 96FG-5 (a good transmitter and input reading) and connected it into wire terminals for 96FG-6 and took 96FG-6 terminals and put them in 96FG-5 terminals. With the new connections, 96FG-6 now read great on all three cores but 96FG-5 read bad. This proved that the transmitter is still good and it is possibly an issue with MAI06 input.

11. I looked in I/O Configurator and all settings are correct and confirmed settings with the other 3 turbines we have.

12. Performed a visual inspection on TCQA, TCQF, LCC/DCC cards. No smoking gun that stands out. I have not see hardly any information on how Mark V interfaces with the terminal cards that incorporate TCQF... It is like it is hardly used. I would love to find a schematic that shows the path. I have seen many different setups and diagrams but none that seem to match our system.

13. My plant chief, for now, wanted us to recalibrate the transmitter to atleast have <R> and <T> accurate readings. 0 Pressure is now equal to 4.24mA (it fluctuates to 4.30mA, not steady) and 400 PSI is now 21.3mA.

14. I also inspected 3PL cable and it appeared fine.

My next step was to swap 96FG-6 (MAI06) terminals and move them to our next open input which was MAI11. Before I do this, I thought I would post and see if anyone has had this issue.

I am stumped. I am not sure where the signal goes from TCQF since I cannot find a schematic, I am assuming to the DCC. Is the MUX skewing the raw data after it is conditioned? Should I try and replace the TCQF card? It is just odd considering 96FG-5, 96FG-4 are reading correctly. And why only <S> core is primarily effected.

I think I covered it all. Thanks in advance.

THANK YOU for a very complete list of the issue and the steps taken to try to resolve the issue as well as the results of the efforts! It is MUCH appreciated.

9. There is a DIAGC.DAT file which MUST match the exact set of cards which are installed in the Mark V. Unfortunately, many DIAGC.DAT files were generic and the commissioning engineer didn't ensure the file matched what was installed in the panel. Or, sometimes when new cards are installed (could it have been that TCQCs were replaced with TCQFs?) the installer must make sure the DIAGC.DAT file is updated accordingly. (Even when changing PROMS on cards (to upgrade to a newer PROMset/revision) it's important to make sure the DIAGC.DAT file is updated. And, really, only GE-Salem, VA, USA, can tell you if the file is correct or not--and, generally, do the updating if necessary.) Your troubleshooting has pretty much narrowed the problem down to the TCQF in <S>--good on you!

I believe, based on Step 10, there is a problem with the MAI06 circuit on the TCQF in <S>. You have replaced the TBQC (which is common to all three TCQFs) and checked the ribbon cables between the TCQFs and the TBQC and they all appear to be okay. As you suggest, you can definitely try shifting 96FG-6 from MAI06 to MAI11 and see what happens; I think it should be fine.

From the MUX (MUltipleXer), the signal goes to an A/D (Analog-to-Digital) converter on the TCQF, so there's not further wiring to follow. If the A/D converter on the TCQF in <S> is getting a bad signal because of a problem on the circuitry of the TCQF in <S>, then it's going to report an erroneous reading. And you pretty much proved than when you swapped 96FG-5 and -6.

As far as finding a schematic, GE only publishes what is in the Mark V Application Manual, GEH-6195, Appendix D, 'Signal Flow Diagrams.' Once the signal gets to a MUX and/or A/D the wiring/hardware ends, so the schematic "trail" does, also. I don't know what version of GEH-6195 you're using, but you might try looking on the World Wide Web to see if there's a newer version available; it probably won't have any more detail on the Signal Flow Diagram, but it's worth having. TCQFs were generally used as an upgrade to TCQAs on panels produced near the end of the Mark V product life. I don't recall exactly what the upgrades were.

Again, GREAT JOB in reporting the issue and what you've done to try to resolve the problem and the result of your troubleshooting--a very methodical and logical troubleshooting progression, using the available documentation and tools (software and hardware).

Hope this helps! Please write back to let us know what you find!

I appreciate the feedback so promptly. Most of us will be gone next week so the issue will not be resolved until the following week. I will keep you updated though. I am sure we will just end up switching MAI06 to MAI11 and update the system. We do have a backup TCQF card, however, the love note attached to it claims last time it was used, the CORES never got to A7...Not worth the risk.

I was using GEH-6195f

In the deep, dark, and dusty corner of our plant, I ended up finding a case wiring diagram of our MARK V system.

<S> Core

TBQC (JBS) routes to TCQF (JB).
TBQC routes to <R> TCQF (JBR) and <T> TCQF (JBT)

TCQF (3PL) routes to TCQA, SDCC, SLCC (3PL).


TCQC routes to other cores from (VARC), (JBU), and (JX) in a daisy chain.