After powering down our Mark V, we can only get <C> core to A4 status, no comms from HMI PC. Any suggestions as what to check/replace? is there any possibility of diagnostics via the keypad/lcd on the <C> core or the 9-pin serial connector on the terminal board of the <C> core?
There's really not a lot of information here. How was the panel powered down; that is, was each processor powered down from the <PD> core before 125 VDC was removed from the entire panel? How was the panel powered-up after 125 VDC was restored to the entire panel?
Was any worked performed on any of the <C> or <R> processors during the outage? If so, what was done? Was the DCC/SDCC card replaced?
Are any of the control processors at A7? Because <C> cannot go to A7 until at least one control processor goes to A7. (A little gotcha that's now very well known. A lot of people try powering up a Mark V starting with <C> and waiting for it to go to A7, but it won't.)
If you can't get any communication established between the HMI (is it a GE Mark V HMI running MS-Windows and CIMPLICITY, or an <I> running IDOS), best to check the LEDs on the ARCnet card to see if they are flashing or not. If they are only flashing periodically, like the HMI/<I> is searching for <C>, then it's likely a problem with the StageLink and/or coaxial cables/connectors. Some sites have an ARCnet fiber optic link in the comm link between the HMI/<I> and <C>, and sometimes that gets confused when power is being cycled on an off. And, as mentioned below, sometimes--for no obvious reason--<C> forgets who it is and needs to be "reminded" by resetting it's StageLink ID and maybe even it's Voter ID--both checkable and settable from the LCC/SLCC keypad and display (see below).
Your best bet for troubleshooting is to use the LCC/SLCC keypad and display's 'I/O States' function. This is covered in the Mark V Maintenance Manual, GEH-59780 and has been covered many times before on control.com. Once you get to the function, use the INC and DEC keys to scroll through all of the "cards" (I say "cards" because on some Mark V panels one of the "cards" is actually a chip on the DCC/SDCC card; you gotta love designers, NOT!). Write down the I/O State of each "card" as you scroll through them all and attack the card with the lowest I/O State first.
The 9-pin serial connector allows access to a low-level diagnostic program on the processor called TIMN. Only GE can really help with deciphering the information available via TIMN, because only they know all of the commands and codes and only they have the secret decoder ring to decipher the information. Some of the information is self-explanatory, to a degree, but most of it is non useful or necessary for troubleshooting and resolving the inability of a processor to get to A7. The best and most useful information is available from the LCC/SLCC keypad and display. I have seen cases where, for some unexplained reason, a processor lost it's "memory", meaning for some reason it forgot it was <C>, or <S> (the 'Voter ID'), for example. That information can be checked and re-set if necessary using the LCC/SLCC keypad and display--and instructions in the Mark V Maintenance Manual. (If the DCC/SDCC card was changed during the outage, then the Voter ID will have to be set, and for <C> the Stage Link ID will have to be set also. A new DCC/SDCC card has to be told which processor it's in, and if it's in <C> it has to be assigned the proper Stage Link ID (check the F:\CONFIG.DAT file for the proper Stage Link ID. And that's done with the LCC/SLCC keypad and display.)
So, we really need more information to be of more help. And, using the LCC/SLCC keypad and display is covered in GEH-5980 and in previous threads on control.com.
Please write back to let us know how you fare in troubleshooting and resolving the issue!