I have bought a Linksys E2500 which clearly says it is "v3" on the label at the bottom.
I tried to flash the firmware image given on the device page (lede-17.01.4-brcm47xx-mips74k-linksys-e2500-v3-squashfs.bin) through the firmware update page of the stock firmware. Maybe that was wrong and I should have flashed via TFTP...
Anyway, the router did not come up after reboot. It still responds to TFTP recovery, but I failed to find an image that would rescue it. What bothers me most is that I even can't flash the original firmware. The stock image I downloaded from Linksys is about 11M in size. However, TFTP transfer stops at 7.53M. The same happended when I tried to flash a Tomato image, which is also ~11M in size.
I opened up the device and can tell at least that the hardware differs from the description on wikidevi. My device has Etron DRAM, not Samsung. I couldn't identify the flash chip, though. It appears to me that Linksys silently changed the hardware specs without labeling it as a new revision?
I have never tried recovery via serial cable and I would need to find someone to solder the pins first, so if you have any other ideas how to recover that device, please tell me.
Take a look at the "Rescue from failed firmware upgrade" page on the LEDE wiki...
For the specifications on your router, see the Techdata page...
I was actually recovering one of these last week. TFTP doesnt seem to be very useful in the case of this router, but recovery via serial is easy once you have a usb to serial adapter.
In the following picture i have,
Orange = TX
Gray = RX
Blue = Ground
Also, i never bother to solder, i twist the wire into a hook shape so it pushes through easy but holds itself in place.
Also, also, the tx/rx holes seem to be reversed on some routers, if it doesnt work the above way try rx, tx and ground
This guide might also be helpful to you, https://www.dd-wrt.com/wiki/index.php/Serial_Recovery
Try DD-WRT images. They're usually robust for recovery (not for usage).
Thank you for your help. I have tried several methods now, but I admit I have given up right now.
I have tried to flash several images including DD-WRT via TFTP, but all failed. I decided to take the risk and try a second router (I had ordered 5 for my project) and immediately flash LEDE via TFTP, instead of the web interface. It turned out that this router is probably not accepting images at all via TFTP. At least I transfered the LEDE image via TFTP, then waited 15 minutes, then power-cycled the router - it still had the stock firmware. Tried another 2 times with the same result. Probably there is some magic required, but I don't know it
So I gave up here and decided to try TP-Link Archer C20 instead. Hope these work better.
I will try serial recovery when I have time. Unfortunately, this revision doesn't have any holes, just soldering pads. I'd have to drill some really thin holes myself. And it has two connectors looking like the one in @JTRealms picture, one labeled "DJ2" and the other one "DJ6".