Good day all. I have a Mark 5 problem that is being a real stumper. I hope that others may be able to shed some light on for me. First a little background. My plant is a 2x1 Frame 7EA's. We have recently come off base load contract and now cycle. The mark 5 with I is 1994 vintage. The symptom has been apparent sometime after 2003. At that time the original flame detectors had been upgraded to GE-Reuters Stokes type with the RS-FSM-1002-002 interface modules. As our application is DLN we have 2 of these modules per unit. The symptom is noise on analog inputs that are unrelated to the flame detectors but terminated to the same TBQC. The flame detectors are powered from 2 sources the R core TBQC. The P core TCTG. I have a DALARM #1322 TCQA ma short circuit voltage too high for R core. The symptoms go away if I lift the wires that feed 24 v from the TBQC to the Reuters modules. However the voltage on those terminals does not come back to its full 24 volt it hovers around 18. 5 (as a comparison I checked the other units terminals and I have a rock steady 24 volts with the Reuters modules attached). I have done the following with no change in symptom so I believe I have eliminated what it is not.

1 Changed the TCQA in R core. Why? Because thats what the book said for that alarm (1322).

2 Changed out the TBQC position 6 on R core. Why? had some issues with screw terminals and wanted to eliminate one nagging questions in my mind.

3 Changed TCPS in R core Why? to eliminate that it was not a noisy power supply and TP4 was at -30 volts and Still is with the new supply.

4 Unplugged the power connector (JT) that supplies 24 volts from the P core with power from R core still attached. Why?Common mode voltages and or noise. To see if unpowering that end would clear the symptom like unhooking the control power from R core cleared it.

I have done a visual and voltage comparison with the other Mark 5 or the good unit in the cab (conveniently located 4 feet away)and have identified the following:
All Berg jumpers on TBQC,TCQA match.

The power supplied from the good unit on TBQC screws # 68 & 70 that feeds the Reuters modules is 23. 9 vdc. On the bad unit it is 7. 6 vdc with modules attached (with modules power wires unhooked from the R core voltage drifts up to 18. 5 vdc and not steady). If these same readings are taken using frame as reference the good unit reads screw #68=23. 9vdc, the bad=23. 73. Screw #70 good unit 0v. Bad = 16. 4 volts. Does this indicate that something is grounded?

Another clue that may be important when the R core is powered down I get the DC ground alarm on the battery charger for that unit. The local DC ground alarm (lamp) on the battery charger Not the mark 5 alarm. When The R core power is restored the DC ground alarm clears. R's power is being switched from the PD toggle switch for that processor.

Any help that can be provided will be greatly appreciated. This problem is not keeping us from running. I am trying to unclutter the alarm list to make it a more effective tool.

 

I found the fix and wanted to share it. Berg jumpers on the TCQA. The R core is just being used as one of two power supplies. The 16.4 volts on screw 70 ref to frame was a floating ground until the jumper was put in to connect it to dcom. Everything works as advertised.

Now it raises the question in my mind about my "good" unit because the berg jumpers for this unit are out for the same MA inputs. If the opportunity presents its self I will need to see where it is getting its dcom reference from. Important lesson learned on my part. Don't always believe that just because both units are the same that they actually are.

 

I'm not familiar with mA input grounding jumpers on the TCQA; only on the TBQB or TBQC. And, I don't presently have access to any Mark V documentation.

Please have a look at the Mark V Application Manual, GEH-6195, Appendix D, and tell us which Fig. the jumpers you are referring to are shown.

 

Thank you for pointing out my error. I meant the TBQC (position 9 of R core). Reference Application Manual GEH-6195D,figure D-22. The BJC that connects NEG on TBQC to DCOM.