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Mark IV C Controller Freeze
Mark IV C controller monitor froze

We have a Frame 6 gas turbine (simple cycle) with MARK IV control system. Suddenly our CRT monitor freezes but machine was running normal with load. Several time we cut off and on the power supply of CRT. Each time it showed the normal display with freezed values. Then we reinitialized C controller then everything was normal. But all counters such as running hour was stopped and again started after C controller reset. There was a 125V DC ground alarm before the problem started.

After C controller reset I found
S125P = 40V,
S125N = -75V

Why C controller stopped and is it related to 125V DC Ground?

It’s impossible to say with any degree of certainty without knowing what Diagnostic Alarms were present prior to the loss of active data.

What happened to the ground after <C> was re-booted?

Was the voltage measured with a voltmeter or from the frozen display?

>It's impossible to say with any degree of certainty
>without knowing what Diagnostic Alarms were present prior to
>the loss of active data.

We were unable to see diagnostic because CRT was freezed with normal display. Auxiliary display isn't functioning.

>What happened to the ground after <C> was re-booted?

After reboot we found
S125P=40V,
S125N=-70V

>Was the voltage measured with a voltmeter or from the frozen display?

During frozen display we didn't see the voltage (because it was freezed). After C reset We saw the voltage in CRT then also measured by multimeter.

Now the voltage is so unbalanced like
S125P=20V,
S125N=-85V
It is fluctuating.

Sometime I found 70V, -30V during heavy rain but it became normal 60V, -60V again. But this is the first time I am getting positive voltage low and it is persistent.

Is it possible to occur any problem in C controller due to 125VDC ground?

Is it a serious problem to machine i.e. positive voltage going down.

Thanks for your quick response.

1 out of 1 members thought this post was helpful...

It's unlikely, but not impossible, that the freezing of the <C> display is related to the ground problem.

If the ground is worse during rain, well, then rain water is getting into some device or junction box which is probably outside of any enclosure. It could even include vibration switches on the L.O. cooler fans (I'm presuming the cooling water is cooled on an off-base cooling water module with large fans moving air over water-to-air heat exchangers, and that the fans are monitored for excessive vibration.

It's extremely common for poor construction practices to allow rain water to enter conduit and junction boxes. But, again--if the ground gets more unbalanced when it's raining it's extremely probable that rain water is getting into some device or junction box which is exposed to the elements (rain water).

I don't have access to my Mark IV materials at this writing, but if the CRT is freezing then it could be a problem with the printed circuit card in <C> which drives the CRT (I seem to recall it's the HVDB, but I may be wrong about that).

MANY Mark IV panels were NOT installed with proper grounding connections and have worked fine for years, decades even, and then started developing intermittent, nuisance problems. It's CRITICAL that the Mark IV be properly grounded with a suitably-sized ground conductor connected to the ground bus bar in the bottom of the panel. MANY Mark IV panels were installed with no ground conductor connected to the ground bus bar; people just thought that because the panel was bolted to a metal structure that was a good enough ground. NOT TRUE. The control panel plinth was painted and so was the metal structure it was bolted to. So, a proper ground is very important--a suitably-sized ground conductor, connected to the plant ground (earth) grid is very important.

Why do I mention this? Because it helps to get rid of electrical noise. And, if you're using radios ("walkie-talkies") in the room where the Mark IV is located they can cause problems with the Mark IV, and one of the common problems was that the CRT would freeze. And, if the control panel doors are open when people are using radios (and cell phones!) that can cause problems with the Mark IV, and CRT, as well. So, consider any possible external causes of interference--such as radios and cell phones. Keep the Mark IV control panel doors closed as much as possible--fully closed, including the printer drawer whenever radios and/or cell phones are being used in the room where the Mark IV is located.

If this is the first time the CRT has frozen, I would suspect either external influences (radios; cell phones) are the problem. Or that the CRT printed circuit card is the cause of the problem. And, if the Mark IV control panel doors are not properly closed and the printer drawer is not properly closed then that could be a contributor to the problem, especially if people are using radios or cell phones in the room where the Mark IV is located.

And if there's no proper ground conductor terminated at the ground bus bar in the rear of the Mark IV control panel connecting the Mark IV directly to the plant ground (earth) grid, then that could also be contributing to the problem.

If you have restored the CRT to normal operation, check and monitor the Diagnostic Alarms. And, use the printer to print the Diagnostic Alarm display periodically during the day to try to capture on paper any Diagnostic Alarms for analysis. A working printer is CRITICAL to the proper operation and troubleshooting of a Mark IV panel--especially if the Auxiliary Display is not working. And a working Auxiliary Display is one of the MOST IMPORTANT "tools" for troubleshooting a Mark IV, especially when it's having intermittent or nuisance problems. Yes, the LED segments do burn out with age, but they can be replaced and should be.

Again, if this is the first time the CRT has frozen, keep an eye on the problem. Also, keep an eye on the Diagnostic Alarms. Look for <C> power supply problems, particularly when it is raining. If there's no proper ground conductor connected to the ground bus bar in the bottom of the Mark IV and the panel is experiencing grounds when it's raining that could be affecting the <C> power supply. Yes, the CRT is powered by AC, but the video signals come from the the printed circuit card in <C> that is powered by <C>'s power supply, which is driven by the 125 VDC battery.

Hope this helps!

Thanks for your elaborate answer.

We finally solved the 125VDC Ground problem. When I got ground unbalance to 3V, -118V; I took a shutdown. First I checked Contact Input Modules. Among 6 CIM I found the problem in CIM3. After a thorough search, actual villain was found and it was 63TK1 pressure switch. It was shorted to its body. Now the ground voltages are normal.

But freezing of C controller is still a mystery. May be it was due to interference.

Glad to hear the ground problem was resolved. 63TK-1 is mounted on or near 88TK-1, which is OUTSIDE of any compartment (turbine compartment; accessory compartment; load compartment).

Interference? You mean electrical noise? Electrical noise is caused by radios and cell phones, and also by poor construction practices (running low level signals in close proximity to high level signals--as defined by GE and its packagers). Good grounding (earthing) is critical to reducing interference caused by normal signal routing, and also to reducing problems caused by radios and cell phones--including keeping the doors closed properly, and the printer drawer closed.

If this is the first time <C> has frozen, it's likely a one-off issue. But, keep an eye on Diagnostic Alarms because if it happens again that's the best way to try to understand what's going on in the absence of a working Auxiliary Display.