7C81 - It appears that I have the wrong BOB, what now?

I can report that all pins behave as I previously posted regardless of LinuxCNC - even while the Pi is booting. One thing I have yet to report is that the first line after running nearly anything with mesaflash is:I don't know if this is meaningful in any way.
I checked my DB25 to 26pin cable for continuity; it works as expected.
Lastly, the amber led on the 7C81 turns on immediately at boot - which I understand to mean a valid profile has been loaded. Perhaps not a surprise, but SPI does seem to be working fine by every indication.

While likely unrelated - I am noticing that power/signals from any source have a ~1Hz "pulse" of maybe 0.03V when inspecting with my oscilloscope.

Please let me know what other diagnostics I can provide.

If _any_ I/O pin is low when the 7C81 powered but not running LinuxCNC
then is is likely that the 7C81 has been damaged.

That's disastrous news!
But I suppose it's a watertight answer for my problems...

I don't suppose you have any insight as to when the 7C8x will be back in stock, would you?

We will have the 7C81T later this year
plus we may have a few boards with solder issues
that can be fixed

It's likely your 7C81 is repairable
Most like U1 is damaged
(Usually from high negative input currents damaging the input clamp diodes)

You can check by measuring the voltage across C14, it should be ~4.2V
Another option is to use P2 instead

I'm measuring:
24.7mV across C14
4.12V across C15
4.16V across C32

I removed the Pi and checked all GPIO on P2 and P7. They read 5V across the board.

That is evidence that the 74CBT16211 (U1) has been damaged.

I like the sound of 7C81T,
are you keeping the RPI header the same as the original?

PCW wrote:

Another option is to use P2 instead

I tried to do exactly that - but instead of continuing to struggle, I thought I'd ask for a hint for how I'd do this. (I think it's reasonable to assume I'm doing it wrong.)

You would need to either use firmware that swapped the connectors
or enable the stepgens/pwmgens on P2 and edit the hal file to suit.

Firmware with P1/P2 swapped

 
 

cakeslob wrote:

I like the sound of 7C81T,
are you keeping the RPI header the same as the original?
 

No, I will offset it since a short cable works reliably