7i97T: isolated output LEDs glow dimly with all outputs off

Hello,

On our 7i97T, five of the six isolated-output LEDs (OUT0–OUT5, next to TB5) glow dimly whenever LinuxCNC is running, although every output is off. The brightness differs from channel to channel, and the OUT0 LED stays dark. Photo attached (LinuxCNC running, all outputs off).

Setup

• 7i97T, firmware 7i97t_7i74d.bin; a 7i74 on P2 with a 7i70 and a 7i71 on smart serial
• LinuxCNC 2.9.10 (uspace), hm2_eth; ssr.00.rate at the default 1000000, all invert-NN 0, all out-NN 0
• 5 V from a Mean Well MDR-40-5 on P3: 4.99 V measured at P3
• OUT0–OUT2 switch the logic inputs of a VFD (Control Techniques Commander CD, about 14 V open circuit, about 1 mA), with OUT+ toward the drive. OUT0 and OUT1 pass through safety-relay contacts. Nothing is connected to OUT3–OUT5.

Measurements (ohmmeter, red on OUTn+, black on OUTn−; VFD unpowered, safety-relay contacts open)

• All outputs off: OUT0, OUT1, OUT3, OUT4 and OUT5 read O.L. That holds both while the LEDs glow and with ssr.00.rate set to 0, when the LEDs go dark.
• OUT3 commanded on: 0.3 Ω (the meter leads), LED fully bright. Off again: O.L, back to the dim glow.
• The LEDs are dark before LinuxCNC starts, and go dark when it exits or the watchdog bites.
• Two days ago, with the VFD powered and the outputs off, its inputs on OUT0–OUT2 read their full open-circuit voltage.

Questions

1. Is a dim glow on the output LEDs with the outputs off normal for the 7I97T? Or does it point to a damaged output driver?
2. If it is damage, can it get worse? Could an output that is off start to conduct? Is there a further test you would suggest?

Thank you.

This is normal for the 7I97T, newer cards have had the LED indicator
circuit changed to prevent this dim glow but, the 7I97T has not had a
board revision to fix this yet, but It's just a cosmetic issue.

Good to know. Thank you very much for taking the time to respond.