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Be sure Your printer can be modified to Chipless Version.
That means You can pass Step 4 of this guide.

Don't buy Activation Key BEFORE You have checked if Your printers Firmware can be changed to Chipless! Follow next 5 Steps.

Step 1
Download and extract Zip archive (How to unzip (extract) files from Zip archive?) with Epson WF-C5790 Firmware  - CV09L3 version

Step 2
Connect printer to PC (under Windows OS) by proper USB cable.
Disable all Epson processes and services. You can do this manually using task manager and administration tools or You can do this via WIC Reset Utility (install and run it, then select MENU -> Support -> Disable processes).

Step 3
Upload Firmware to printer in the NORMAL MODE (do NOT use service mode yet just start the printer with the power button). Run EPFWUPD.EXE file and follow all steps until Firmware will upload in printer. 

When Firmware Update process is complete - printer will restart - usually it will take only a few minutes but can continue for 10-20 minutes in some rare cases. 
If process hangs or stops at 80-99% - replug power cable and start printer manually.

Step 4
Now check current firmware version ( how to check ).
If firmware version is CV24M3 - firmware has been uploaded successfully. You can go to next Step.
If NO - restart the printer and try once more time.

What do You have to do next after uploading chipless firmware?

Step 5
1. Buy this Activation Key
2. Download License.exe application (Windows only). Password to extract - 12345.
3. Run License.exe under Windows and press Activate Online button
4. Input Activation Key and press Ok!

Please keep in mind - there are 2 types of keys:
- Regular Activation Key (HAS expiration date of using);
- No Expiration date Activation Key (can be used whenever You want in 10 years).

Buy Activation Key in case You have uploaded Firmware to Your printer successfully!

Prices and discounts:

Regular Activation Keys (HAS expiration date and couldn't be used after has expired):
1 Activation Key - $50
5 Activation Keys - $48 per Key
10 Activation Keys - $45 per Key
20 Activation Keys - $40 per Key
50 Activation Keys - $35 per Key
100 Activation Keys - $30 per Key
You can pay by PayPal, Visa, MC etc. :
Here or Here

NO EXPIRATION Activation Keys (has NO expiration date - can be used whenever You want):
1 Activation Key - $55
5 Activation Keys - $53 per Key
20 Activation Keys - $50 per Key
You can pay by PayPal, Visa, MC etc. :
Here

If You have any questions - You can read or place Your questions at Chipless thread at our Discussion Board - https://forum.2manuals.com/index.php?/topic/80414-chiplesssolutions-chipless-firmware-for-epson-printers-chip-virtual/