This is a nice 600DPI PostScript laser printer from 2012- 10 years ago. 
* WIFI can be joined, USB recognizes its name on a MAC computer, Also Linux
Ethernet Cable registers on the 16 character LCD screen as Connected, With Address.
* Self-test Printing works fine from front panel delivering a nice report
BUT– It refuses to print through any interface  No BUSY light or anything
Bit o’ Research shows it has a primary circuit board to manage all this, I have to guess that’s (ir)responsible for this Problem.
I did spend some time monkeying around with the cursor keys and LCD display to reset the ROM, reset factory defaults et cetera et cetera… To No Avail.
Looking back now I might have considered trying to upgrade the firmware to see if that made any difference – I doubt it but only realised a firmware upgrade was available after replacing the motherboard. “maybe try that next time Paule”

My subjective impression was that there was no association between the printing part of the machinery and the outside interfaces.
I took the side panels off the checked the many cable connections for loose fit, burned chips, etc. and All seemed fine.
Nowthen– Curiosity aside, what is it worth spending to fix this? Surprised to learn on Ebay that these things come in at least $150+shipping. 
Refurb Toner Cartridges, if needed,  are not prohibitive– $17.00
Found a free return refurbished spare controller board on eBay (warranted) for $40- the upper limit of what seemed worthwhile.. 
the part happened to be labelled: 
B512342-5
I did find a dealership service manual online with excruciating detail about screw torques, Wire color coding, even a section on attaching a debugging port to the main circuit. 
Interesting: But Helpful?
Nothing of the surface mounted components would I try replacing. I have had dismal failure own that front, before….
Why look for Problems one has no direct solution for?

First thing to do was a Google Image Search for the card ID: to see whereabouts this thing shows up- Well several versions did show up- the -5 suffix is some kind of versioning because lower numbered revisions actually used some real estate on board for a Centronix Parallel Port- My circuit board only had the solder pads for that, But with USB and Networking, who needs parallel? It woudl have been easy to cut the case to match but… No, Paule.
Yes, by 2012 that was all Over, but the design obviously went further back.

Cuts a long story Short- 
– Before removing a circuit board I always label it OLD with a Sharpie
– The NEW or rather Refurbished one was so very similar I knew I was likely to screw up!
– Several zoomed photos to show plug color, location and wiring, though in this case nothing could be mis matched.
– two ribbon connecters made me think they might be the type that has a ‘captive’ clasp on the plug. The ribbon had a hard blue plastic card end-backing it seems in order to allow push and pull insertion and removal (AKA: Interference Fit) without whacking the cable.
– I usually pop out the white connectors with a screwdriver blade prying each side in turn Could fin no ‘retainer’ — some such plugs have a tint patch that needs to be pushed to release the connector. Not these.

Alright so the Printer is back together- It DOES take some puzzling to do this, but it’s OK.
On power the LCD showed ready but griped about the Electrostatic Drum being ‘End of Life’ which it never said before. I think this was an ‘ancestral memory’ of the Printer it came from. My Guess: That whoever recycled the printer this board came from gave up ion that Message on seeing the Brother price for a Fuser/Elctrostatic Toner unit was $80-$90
NOT worth it fro them! the LCD does allow resetting this to 0, and No More COmplaints

The former Page Count had been 80,000, it now dropped to 55,000 as the NVRAM on the board ‘remembers’ its old life

Also, the serial number label on back of this printer is now WRONG

and YES it DID take a Firmware Upgrade to 1.25- Wish I had tried this first with the Old Board though I suspect it was un revivable. AQt 10 years old it seems Brother is still happily supporting these units, and even successfully upgrade the Forward from a very modern MacBook M1!- also the Printer Preferences Found and Used this printer without further intervention

I. can see the high price of this laser printer comes from its ability to handle Postscript, lots of internal fonts an compatibility with several other Printer Standards from HP (Laserjet) its ability to be used in Windows Workgroups etc. It dod NOT seem to have AFP (Apple Networking) however.. 

This describes an instrument to check allsorts of different cables. This is

 an ethernet cable being checked,
Although the RJ11 ethernet plug has got eight conductors only four are needed for basic network communications two receive and two transmit pairs wired 1 to 3 and 2 to 6 both ways as in this testing Rig. Conventional ethernet cable can be up to 600 feet long so you would simply flag the yellow terminator in at one end and the blue box at the other to test the continuity of DC voltage. It does not do much checking for resistance between the leads as might happen if water got in to the conductors as it does not really measure resistance very well but it would for example show you if you had a defective plug if you wiggled it in the connector…
The display shows the simplest cable having wires 1,2,3 & 6 all connected but the other four conductors not. This will not operate at gigabit speeds– that will need all 8 connected!

some remote Wi-Fi equipment for example can be powered through the ethernet cable using a technology called POE. Note that it is not as simple as just pushing some voltage up the wires because the specification makes allowance for line resistance and proper correction for voltage drops with special terminating gear..
the DC voltage ‘rides under’ the high frequency communications on some of the same wires.
This is especially important for those Wi-Fi antennas and powered relays that are way up high in trees  for example

Or– How to go about discovering the remedy to this diagnostic from the garage: “Sway Bar Boots Cracked”
What IS a Sway Bar? I have another article on How to Google, but this is not the place for that. A bit of Research goes a long way to seeing what is being referred to.
I *DID* find a very good page about this here but let’s go on
Basically it is a mechanical coupling between the wheels on either sides of a vehicle IF they are NOT on a common axle,
which is true of most front wheel drive cars which have SEPARATE axles per drive wheel,
or independent suspension cars like the old VW van which has rear wheel drive, an engine in back and two lonely independent non-driven front wheels-
and a long piece of torsion bar across and between these two
( fixed a bent on in the Australian Outback many years ago!)

Now to the Specifics- this is for a 2000 dodge caravan where the garage reported during an oil change
and quotes $256- Most of this is likely labor, in our area, about $100/hr. I happen to know that under most cars, movable parts are protected by shields, boots and guards– Or they should be.
a Boot looks like your shoe indeed, has bellows-like flexible moldings or a concertina finish, and, tellingly, needs to be threaded over a shaft or bar to install or remove.
However, some clever Dicks have invented snap-on wrap-around Boots to protect moving things from road dirt ingress that can be fitted without removing said bar to re thread things..

But Wait- If the boot is busted, dirt may already have got in and ground down some part of the joint?
Now it’s time for Youtube. Often as not in this situation, you would want to inspect the couplings to see if indeed the unguarded parts have been invaded with dirt. This can involve some tricky disassembly.
If YES, which is Likely, almost certainly wear and damage will have occurred- In fact, let’s just assume it is So, and the job of replacement Looms.
Here are some YouTube searches
Looks too expensive or difficult for that old car?
How about just washing out the old lube+ gunk with spray grease solvent or steam clean, re-up the Lube and new snap on boots?

This is like the “Watchful Waiting ” doctors often advocate where the a procedure will be more trouble than it’s worth- especially– and I hate to say this– as you age : )

Consider the sometimes surprisingly low cost of a total part replacement- Maybe more than is actually wrong, but complete with the bushings, boots and everything– Head on over to Amazon and or your Local Parts Store!

And

Good Luck!