Your mentioning cloning to a SD card and liking puzzles is interesting. One of the two (A) N810's I bought is like new, but has a bad micro usb port. The other (B) is kinda rough, but works perfectly.

(A) Has screwed up WiMax OS and, although connects to wifi, cannot access application catalogs.

(B) Connects to wifi and accesses application catalogs normally..

As I cannot connect pc to tablet with usb on (A) to flash,

Is there any way to flash (A) with SD card?
or,
Is there any way to clone (B)'s OS to a SD card and use in (A) to boot from?

I haven't been able to find a disassemble guide for the N810 to fix the usb port on (A) and don't know if I would attempt to anyway.

ok.
Now I really need to have a crystal clear understanding 1st.
You mention that you have 2 n810's?
I thought it was only one you were getting...
I didn't realize you purchased a pair of n810's...
If this is so...that was smart.
If my understanding is in error here please say so before I start going indepth into solutions that are not possible at this time for you.
In short..If you do have 2 n810's then yes you can pop in and use an os cloned sd card from another n810 ...
However it does not solve the problem of the issues of the n810 which needs reflashing, and proper setup.
And you would still need to install the proper boot loader to see the os on the sd card when it starts up.
You are starting to think outside the construct ...which is good.
here is a more concise (albeit short) thread on this particular topic.
http://talk.maemo.org/showthread.php?t=15374
Which will solve your problem.
There are other threads elsewhere here at talk maemo.
use the "Power Search" to the right ...in the column of on site links to find answers to questions.
Query "wording" is everything to finding the right answers for a specific solution for a specific problem.
And it is not as difficult as it sounds...although the process may appear daunting to a new person it isn't rocket science...and this little puzzle would speed up your learning curve and
You also have an edge with having the other n810.
Speaking of the problematic n810.
you mention it has wimax os on it?
Pop the back cover off
Pop the battery out
write down the info from the plate in there and compare/look-up what you see.
ie- n800= rx34 , n810=rx44, n810 wimax= rx48
It may be flashed with the wrong firmware...for the wrong device model.
the firmware in these lists....
https://web.archive.org/web/20131117...ev/nokia_N810/
for example... meant for a standard n810... will start with rx44 as can be seen.
which won't help for sure with issues.
Clearing that issue up may result in full functionality.
As far as application manager (from now on in conversation referred to as "app. man.") goes.
I'm betting the firmware isn't helping.
Also I'm betting the catalogues in the app. man. are nokia catalogues.
Which are gone.
They don't work.
Also I'm betting that even "maemo extras" catalogue isn't enabled.
Hence ...the most probable result is....
App. Man. "seems" broken.

1st thing.
Deal with the firmware issue...and flashing issue.
By the way...I know that you said the problem n810 won't connect via usb...
What have you tried?
Just plugging it in?
have you attempted to flash the firmware with the cable yet?
Give it a shot.
Make sure you know exactly which firmware you need 1st.
and have all pertinent stuffs ready as per flashing instructions found everywhere in the wiki, here at talk maemo, and my walkthroughs...first.

don't just hope to ride a half-solution like running an os on sd card... on top of another previous individ's created problems.
T
hat will lead to frustration and heartache.

After that flashing issue is properly dealt with ..all else is easy peasy

I bought two on Ebay in case one wouldn't work I wasn't aware there were two models. One was regular, one was WiMax. The regular one looks worn, but works as it should.

The other,

Model N810
WiMax Edition
Type RX-48

This is the one with the bad micro usb port. I think it is a lost cause, as I can't flash without the pc connection. I will probably attempt to fix or replace the port itself, as it is pretty useless as is. I have done minor repairs, like replacing capacitors in TV's, so will see if I'm up to it. Only paid $23, so no great loss - although it looks like new with a perfect screen. Luck of the draw.

It will sometimes (seldom) connect for a few seconds if you wiggle and hold it, but it immediately disconnects. I know the cable is good as it works fine on another one.

Well considering you have an excellent practical background/understanding...
looking on ebay will net you a replacement usb port.
It is much easier to replace the usb port than the n900 port.
the cost "may" be practical for a replacement port.
or another beater n810 to pillage for parts would do.

Or you could just pillage the screen and other parts...keyboard...the body...for your normal n810.
Or you could pillage the normal (beaten) n810 for the usb port and other sundry parts...
Of course it could end up you have crappy luck and then neither will work
But I doubt that will happen with your expertise and understanding...
Still...hm
Anyway
$23 isn't bad for essentially... complete n810 parts.
Your choice.
Frankly I'd try to find a replacement usb port and fix the usb 1st.
Failing that...parts.

I would like to 1st try to replace the usb, 2nd swap the parts, but haven't found any instructions on taking the thing apart. There's always the challenge of trial and error.

youtube possibly has a vid tutorial on disassembly.
I haven't done n810 tear-down in forever...
Hunting would find what is needed I believe.
I'll do some looking tonight as well and see what I dig up.

I would highly suggest filming your tear-down.
That way you can see how you took it apart and hence can reverse your steps to put it together again.
For that matter ...when putting it back together...film that as well.
Film it all.
Post it on youtube as well.
The more walkthroughs there are the better.
It helps the next people...

Couldn't stand it.
Had to look.
Me and puzzles...
here are manuals pertaining to the n810.
http://www.s-manuals.com/phone/nokia_n810
and this site has it for the wimax n810 as well..
http://www.cpkb.org/wiki/Nokia_N810_...atics_download
then there is this as well..
http://www.automotoguide.eu/nokia-n8...air-manual.pdf

there appears to be a n800 tear down on youtube...
https://www.youtube.com/watch?v=I3BorZkQ2Vo
haven't found a vid for n810 yet...
If you film the tear down and reassembly..and post it on youtube...it may be a first.

Wow! I searched for hours with no luck. These are exactly what I need.

Thanks

when searching on the web for n8x0 related content....
keep it concise.
don't limit your search to just one wording.
try the same query in multiple ways.
for example typing "nokia n800" will get you nokia 8 and nokia n8-00 responses as well...muddying up your results more.
also it is vague.
typing "nokia n800 internet tablet" or "nokia internet tablet" even ...
will narrow things properly.
typing "nokia n810 diablo --- (one or a couple words associated with specific query ie- disassembly ..) will help narrow results...
combinations...different wording for the same thing will also narrow the results.
go to my walkthroughs...somewhere in them is a direct link to my google drive.... for a folder... my nxx0 browser bookmarks and add them (import them) into your browser...
there may be a few that recently I came across that aren't added (I'll have to update it soon)
inside the browser bookmarks are subfolders pertaining to just about every topic ever needed for you... and inside ...requisite links.
It would make your hunting almost unnecessary...
and would also make study more enjoyable.
Actually ...here is the link to the google drive folder in specific.
https://drive.google.com/folderview?...npiS21hSmtBRXM