Earth Fault Alarm on Sunny Boy

I have a residential installation with 2 PV arrays feeding 2 separate Sonny Boy SWR2500U
inverters (SMA.) One of the inverters is showing the red LED Earth Fault (GF) preventing
power output. Manual states that with only red LED lit, the GFDI fuse is blown; if red
and yellow LED lit then indicates actual GF. Fuse checks good. The display
shows the normal diagnostics sequence when powered up or powered down. The
source voltages show in normal range: 322VDC, 240VAC.
I lifted the ground wire off the inverter frame coming from the array and powered up
unit and still get the red GF LED. With this wire lifted how can there be GF current flow?
There is a separate GFDI sensing board that sends
the signal to light the red LED on a GF. I suspect this board is bad. Has anyone worked
on this particular inverter and can shed some light?
Thanks in advance.

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