7i77 not detecting all of a sudden

I've contacted mesa directly regarding this but would be happy for any insight.

I finally got the basics working on my biesse rover conversion. The pc with the 5i25 was set up about a year ago and I connected the axis motors to get them running in a basic state, no runaways, that kind of thing. I've been working towards getting the (new) axis motors installed on the machine and yesterday I got the three axis servos installed finally. Last week's job was getting estop and encoders wired neatly.

So. Here's the problem. After finally lugging the massive x motor into place and getting it bolted up I was very excited to finally see this machine move under its own power. I've had the control cabinet and pc powered up regularly over the last few days getting the estop sorted. Testing the drives function as expected etc. The pc was last functioning on Friday evening, jogging the axis motors etc, I haven't made any changes to the pc since.
Now I'm getting an error when loading linuxcnc.

linuxcnc analogue0.scalemax not found

So the 7i77 isn't responding. Cr1, 6 and 7 are lit. There's no field power connected to the 7i77 at the moment. Only connections to the. 7i77 are the three encoders and their 10v analog and drive enable.
Power is supplied by the 5i25. I've checked the jumpers just in case, they're set correctly as you'd expect, the set up was working a day or so ago.

I tried the 5i25 in another pc to test. Swapped the hard drive first, booted it up, Linux booted up correctly. Then I installed the 5i25 and the pc wouldn't even boot with the card installed, just to confuse things. Reinstalled everything back in the original pc and it booted up but still wouldn't load lcnc. So there you go.

Is there any basic wiring I might have stuffed up that could damage the card?
Should I try powering the 7i77 with a 5v supply?

Any steps I can take to test things?

You may need an external 5V supply depending on the current draw
of the encoders. If you power the 7i77 from the 5I25, you should verify
that the 5V is OK at the 7I77 (you can measure at P1)

"analogue0.scalemax not found" means the analog section that is powered
by the 5V is not operating. This could be a 5V power, cable 7I77 or 5I25
issue.

Measured 5v on the parallel cable. Pins 18-25. The 5i25 looks to be supplying power.

Loaded the 5i25 from the command line, show pin shows 10 encoders and 0-33 gpio. The 7i77 io should show at this point from what I understand.

Does the field I/O show up if field power is present?

If the 7I77s CR6 and CR7 are on (yellow LEDs near the center of 7I77 card)
the means the analog section is powered and out of reset
So it could be a cabling problem or other problem in the serial
data path from the 5I25 to the 7I77 and back

The field power was applied when I loaded the card and showed the pins.

can you post the result of:

sudo mesaflash --device 5i25 --readhmid