Mesa 7i76e damaged expansion port?

Hi Guys

I am currently building my first Linuxcnc powered milling machine and the problem i`m facing now led to the first forum post in my life.
I use a Mesa 7i76e and added a 7i85 for the encoders. A while ago, I have set up all the servomotors and could even get them to run with the encoder feedback (encoders only update the DRO for when i want to mill by hand, without the motors). 
Unfortunately, a live wire touched one of the two boards and a bit of magic smoke got released. I didn`t see where the smoke emerged and i don`t see any damage on either board (but the amount of smoke should indicate some visible marks). Now my Encoder counts don`t get recognized by the Mesa cards. This is my current situation:

- I watched halshow and neither rawcounts nor any other counters see anything. 
- The encoder on the 7i76e still counts correct. This let me believe, that the encoders and wiring are good.
- The .hal file should be of no concern to me, correct? Halshow shows all 5 encoders but only Enc04 on the 7i76e counts.
- I bought a new 7i85s (7i85 were not available) and the new card doesn`t count either. (I flashed the correct bitfile)
- I put the 7i85 as well as the new 7i85s on the second expansion port and neither of them counted. (I flashed the correct bitfile)
- I tried to use one of the stepgens on the 7i85s but got nothing. (Tough, this one could be on me with a wrong configuration)
- I unfortunately don`t have another ribbon cable at hand. Is it possible, that the cable got damaged? I doubt it.
- The jumpers on both cards should be set correct (to RS422, power supply via exp port) and haven`t been changed since it worked in the beginning.

My question: Is it possible to force a sign of live out of the 7i85? Or somehow get proof, that the card gets "recognized" by the 7i76e? I would like to avoid unnecessarily buying a new 7i76 since they are hard to get and pretty expensive. Can I test something with a multimeter?

I`m grateful for any thoughts or ideas. However, my knowledge about electrical circuits is pretty shallow and even worse around software stuff (I hate Linux with a passion even tough I love the idea of an alternative to Microslop).

Thanks and greetings from Switzerland

P.s. I saw another post and it seems there is a terminal comand where you can force some response or a dump of specific components on the card. But I really didn`t understand anything going on.

You can do a quick check of the expansion port condition with:

mesaflash --device ethernet --addr IP --rpo 0x1004
for P1
and:
mesaflash --device ethernet --addr IP --rpo 0x1008
for P2

Where IP is 10.10.10.10 or 192.168.1.121 depending on 7I76E setup

Both should respond with  0001FFFF (with nothing connected)

Typically what would be damaged from this kind of a fault would
be either U3 (P1) or U20 (P2) = 74CBT16211CDGGR

P1 (U3) damage may show up on P2  (U20) as the chips share a low current
4 V power supply and a damaged chip may short this supply so the undamaged
one also shows a fault.

Thanks a lot for the fast response PCW

Both comands returned 00000000 (when lncnc is running in the background, the operation is not permitted,right?).
I take it, this means there is no response, or a faulty one. Now I can see some slight color degradation on top of U3 compared to U20, which i brushed off as dirt before. But it`s probably from the accident.

Is there anything else to test before trashing it? I don`t think anyone in Switzerland is doing PCB repairs, and if they do, a new one is probably cheaper.
Since the 7i76 is replaced by the 7i76eu, I will have to get the new one (if it`s even available atm). Is there any major change between them, or can I more or less leave the .hal file as is? I probably have to change the name everywhere, but as far as I know, the rest should be working the same way.

Thanks again for your help. I see your profile on every second post on this site and it helped me countless times before. I appreciate you taking the time to support so many people.

P.s. Is this "rpo 0x1004" something one should know, or is this more of a manufacturer inside knowledge?

Yes, 000000 Indicates the likely U3 has been damaged and is shorting out
the shared 4V supply so U20 and P2 will not work either.

I'm surprised that there is no SMT repair facility available there. We routinely repair
minor faults like this for a nominal fee ($35.00), but of course shipping is s killer.
(the part is about $1.00)
 
EDIT:
Its likely that if you simply removed U3, that the other port would work allowing
you to connect the 7I85 to P2.

The 0x1004 is simply the register address of the GPIO port that's connected  to P1.
It should be all ones = 0x0001FFFF when unconnected because the expansion
GPIO ports on a 7I76E have pullup resistors and all GPIO is set to input mode
at power up or watchdog fault. All 7I76E firmware is open source and the low level register
addresses/functions are provided in the regmap file in the source directory of the 7I76E
software support zip file.


The 7I76EU is a one-to-one replacement of the 7I76E, no hal file changes are needed,
unless you want to use one of the new features.

Hi

Im based in switzerland and could give it a shot with repair by replacing U3, if i know what chip it is

The part number was in my first post = 74CBT16211CDGGR