On a Frame 7FA or 9E, the control story is not a ladder file you can print from a USB stick. GE Mark VI and Mark VIe run the turbine as function-block application software: fuel, IGV, acceleration, exhaust temperature, flame, overspeed, and trip logic all live as interconnected blocks inside a passworded project. If you only see HMI setpoints, you are looking at the skin of that application—not the blocks themselves.

That distinction matters during an outage. A dead I/O pack, a swapped terminal board, or a controller card that will not boot is a hardware problem. A unit that will not fire because a flame-scanner block is voted out, or that hangs on a start because a compressor map block sees an implausible pressure ratio, is an application-software problem. Mixing the two wastes the window.

Typical GE turbine-control stack: network switch, field terminal board, I/O packs, and rack controller/communication cards—the hardware the function-block application actually executes on.

Mark VI and Mark VIe are not the same rack

Field conversation still says “Mark VI” for both generations. The application idea is similar—function blocks compiled to controllers—but the I/O and network are not.

Classic Mark VI is VME-centric. Controllers talk to I/O over the GE Genius bus; VCMI cards handle that I/O network; operator stations sit on Ethernet. Mark VIe moves I/O onto Ethernet, uses UCVx-class controllers, and pairs I/O packs (IS220 / IS200 families) with terminal boards that land field wiring. ControlST / Toolbox ST is the engineering environment for both lineages in current plants, but a board pulled from a Mark VI VME crate is not a drop-in for a Mark VIe pack.

When you are sourcing a replacement, match the generation first. Controller blades, I/O packs, and terminal boards for these turbines are listed under GE boards and turbine control.

How the application is actually organized

GE does not publish a public encyclopedia of every block used on a specific Frame 6B or 9FA. The live definitions sit in the site’s Toolbox ST project, behind license keys and controller passwords. What you can discuss honestly is the functional map every heavy-duty gas turbine still implements, regardless of the exact block name stamped in that project.

Process blocks close the loops the machine lives on: compressor performance and IGV, fuel-split or gas-control-valve demand, acceleration and deceleration ramps, and exhaust-temperature or spread control. Selector and voting blocks sit in front of those loops so a single noisy transmitter does not become a trip. Timer and quality blocks delay sensor-fault declarations so a one-scan glitch does not dump the unit.

Protection blocks are a separate layer. Overspeed, flame-scanner voting, wheelspace or bearing metal temperatures, and vibration from proximity probes do not “tune” the turbine—they decide whether it is allowed to run. Trip-solenoid and emergency-stop paths are deliberately simple compared with the modulating fuel path, and they should stay that way.

Reading the program versus reading the HMI

Operators already see trends, alarm setpoints, sequence-of-events, and I/O diagnostics on the Mark VIe HMI. That is enough to confirm a flame-out, a failed RTD, or a pack that dropped off the network. It is not enough to change how a selector votes or how a compressor block calculates surge margin.

To open the function-block diagram you need Toolbox ST (or the ControlST suite your site is licensed for), a hardware key, and password access that GE or the OEM granted under the plant’s service agreement. Unauthorized dumps of application software can void support and violate GE intellectual-property terms. If the site does not have that access, the correct path is GE Digital / Vernova support or the authorized distributor—not a copied project from another unit.

Documentation that actually matches the installed software is still the Mark VI / Mark VIe installation and application manuals (the GEH series your outage binder already cites, commonly GEH-6721 for Mark VI install). Frame-specific application notes from the OEM beat generic block lists every time.

What this means on Frame 5 through Frame 9

The same block categories appear on Frame 5, 6, 7, and 9 machines because the physics is the same: a compressor that can surge, a combustor that can lose flame, a rotor that must not overspeed. What changes is the I/O count, the fuel system, DLN versus diffusion, and whether the rack is Mark VI or Mark VIe. A technician who understands voting, ramps, and protection layers can troubleshoot across frames; a technician who only memorizes one project’s block names cannot.

Vibration channels on these units usually terminate in a separate monitor—often Bently Nevada proximity probes and a 3500-class rack—then a trip or alarm contact into the Mark VI. Do not hunt a shaft-vibration problem only inside a turbine function block if the probe, extension, or monitor is the failed piece.

A practical stance for outage work

Treat function blocks as the control law, and treat packs, terminal boards, and controller cards as the execution platform. If the law is wrong, you need licensed Toolbox access and an OEM-backed change. If the platform is wrong, you need the correct IS200 / IS220 / VME part, not a rewrite of COMPHYS. Most forced outages I have walked were the second case.