MARKV: R core A8 status and Bad EEPROM Checksum Error

Mark V TMR system is installed on our site for Frame V gas turbines. Mark V was initially configured with <I> but in 2008 <I> was upgraded to HMI. Two gas turbines are installed at our site and each gas turbine has its own HMI in the GT compartment and we have one HMI in the control room for both the gas turbines for displaying data. The fuel used for the gas turbine is Natural Gas.

Both gas turbines are running and their last maintenance was done in Jan 2015. On the morning of Oct 30 2015 it was reported that the some exhaust thermocouples are showing bad readings on HMI. We rushed to the control room. When we checked the status of R core it was in A8 status. Can anyone explain what is A8 status? Why R core went into A8 when it was running in A7 status since January?

We restarted the R core from <PD> core. It booted up successfully and attained A7 status. Just after one day it is showing the DCC error(DCC Bad eeprom table checksum). Can anyone explain this error? Can we relate this to A8 status of the R core? Can we expect rebooting or any other problem in R core?

In help HELP_QD.BAT file i have found the following details<pre>

CAUSE A bad checksum was detected for the EEPROM.

EFFECT Core powers up in default mode with control function disabled.

ACTION Check from <I> as to which EEPROM table has the bad checksum and download correct table.</pre>
What is meant by Mode Control function disabled?? And when will this EFFECT take place? On re-booting?

About 125VDC: It is grounder. There is some problem in batteries. Hopefully these batteries will be replaced in next shutdown.

TCPS card of S core was replaced due to rebooting problem of S core. This was done in Feb 2015.

Very good background information; thank you!

On a TMR Mark V, approximately one-third of the exhaust thermocouples are connected to each of the three control processors and if <R> was found to be at A8 then it's likely TTXD1, TTXD4, TTXD7, TTXD10, and so on, were found to be showing negative values (which is the default for bad signal quality in the Mark V CDB (Control Signal Database)).

The Mark V Maintenance Manual, GEH-5980, has some explanations of the various status indications for the Mark V processor, and if I recall correctly (I don't have access to GEH-5980 at this writing) I/O Status A8 is an "undetermined" status--meaning something pretty serious has occurred and the Mark V operating system (the one running in the turbine control panel) can't determine what has happened. It's unusual for a running processor to go to A8, but it has happened (obviously; it's happening at your site).

The information about the 125 VDC battery ground is very useful--because 125 VDC battery grounds can wreak havoc with the processor power supply cards (the TCPS cards) which can make the DCC/SDCC and LCC/SLCC cards experience problems--and even failures. Some of the older TCPS cards are known to be experiencing problems with components (usually capacitors) and battery grounds can make this condition worse.

Running with a grounded 125 VDC battery may be necessary, but it's not advised. If one or more of the battery cells is truly grounded that's a pretty serious problem--as they should be sitting on insulated material (rubber, plastic, wood) and/or an insulated metal battery rack.

Remember: the Mark V turbine control panel <b>IS NOT</b> the only thing the 125 VDC battery provides power to. In fact, the 125 VDC for the Mark V turbine control panel (and its I/O) is usually powered by the same 125 VDC power distribution panel breaker as the one that supplies the Generator Control Panel (which is usually mounted directly to the side of the Mark V turbine control panel). Usually, but not always. Even if the Mark V turbine control panel is fed by its own separate 125 VDC breaker in the 125 VDC power distribution panel there are very likely other systems and devices which are also powered by the 125 VDC battery--in particular, the DC Emergency L.O. Pump, and in many cases, the fire detection and discharge systems, as well as some Emergency DC lighting in the Accessory and Turbine Compartments (and sometimes the Load- and Generator Collector Compartments).<pre><b>A ground on any device or circuit powered by the
same 125 VDC source(s) as any digital Mark* Speedtronic turbine control
panel is detected and annunciated by the Speedtronic turbine control panel.</b></pre>That's contrary to popular belief and common mythology, and it's very important to understand. And, it can include any "auxiliary" 125 VDC power source(s) for the Speedtronic turbine control panel--including <DACA>s, which are sometimes provided with Speedtronic turbine control panels (which convert AC to nominal 125 VDC).

The Mark V, in this case, can't distinguish between grounds on I/O connected only to the Mark V (and, specifically, ONLY I/O that's powered by 125 VDC, such as discrete (contact) inputs, and solenoid outputs, and the fuel trip and IGV solenoids) and other devices and circuits which are powered by the 125 VDC sources. So, it's really critical to know where the ground is located--and sometimes the ground is NOT something connected to the Speedtronic turbine control panel (not very often--because the majority of I/O on a GE-design heavy duty gas turbine is connected to the Speedtronic turbine control panel).

The most likely cause of the problem experienced earlier this year which caused the failure of the <S> TCPS card and the one you're currently experiencing (which is most likely related to the <R> TCPS card) is the 125 VDC battery ground. Finding and fixing that is most likely going to save the expense of replacing more TCPS cards, and possibly even a turbine trip, or three (or four...).

It's possible to keep replacing TCPS cards, but they're costly and that's not solving the real problem. The Diagnostic Alarm troubleshooting help presumes the 125 VDC supply(s) are ungrounded--and that means the battery and any devices or circuits which are powered by the SAME 125 VDC source(s). Finding and resolving the root cause of problems resulting in printed circuit card failures is always more cost-effective--in both the short term and the long term.

So, it's likely that the ground is causing the <R> TCPS power supply to have intermittent outputs which is causing <R> to reset itself while running, and since control processor RAM is lost when the processor re-boots (for whatever reason) it's can't remember why it re-booted.

It may be possible that the battery ground and the EEPROM Checksum errors are unrelated--not likely, but not impossible. In that case, replacing the DCC/SDCC would be necessary to correct the problem--but if the battery ground and/or a failed or failing TCPS is the root cause of the failure of the DCC/SDCC component(s) then the new DCC/SDCC card may also fail prematurely for the same reasons.

Hope this helps! Please write back to let us know what you find, and how you progress with resolving this problem. Troubleshooting grounds on a digital Speedtronic turbine control panel <b>IS NOT IMPOSSIBLE</b> (again, contrary to popular- and mythical belief). It just takes a good understanding of the entire system (the battery charger(s), the fact that 125 VDC is typically used for other devices and circuits than the Mark V, and the fact that only those devices and circuit connected to the Mark V <b>and</b> powered by 125 VDC can cause battery ground alarms (when it's a device/circuit powered by the Mark V). So, LVDTs, servo-valves, T/Cs, RTDs, pressure transmitters, speed pick-ups, vibration sensors--anything which is NOT powered by 125 VDC--cannot cause 125 VDC battery ground alarms. Which eliminated a LOT of I/O from having to be checked. Digital Speedtronic turbine control panels can operate with grounded or ungrounded T/Cs, grounded or ungrounded RTDs, etc.--so finding a ground on one of these devices is NOT a problem, especially not when trying to troubleshoot a 125 VDC battery ground alarm.

Most 125 VDC battery ground alarms on devices or circuits connected to digital Speedtronic turbine control panels are on devices or circuits which are external to the turbine and generator--like Cooling Water Skid fan vibration switches, or Cooling Water Pump discharge pressure switches. Note that the 125 VDC battery also usually powers the generator breaker trip/close circuits (though grounds are not usually found there, they have been). Again--any device or circuit which is powered by the 125 VDC source(s) which also supply the digital Speedtronic turbine control panel and which develop a ground will cause the Speedtronic to annunciate a 125 VDC battery ground--not just devices and circuits connected directly to the Speedtronic.

Many times troubleshooting is a logical process of elimination until you finally arrive at the source--and <i><b>especially</b></i> when troubleshooting grounds.

Go forth, and conquer!

Thank you for the explanation. I will write back as soon as we will perform any activity. Meanwhile same DCC error has annunciated once again. The alarm just appears for one or two minutes and then disappears.
Hi all,

Exactly the same problem I had a couple of months ago - A8 state of <S> core. Had to replace DCC and LCC cards (loc.1).