We have this in our cashiers station. We tried processing a check for $650,000.00. However, we were only limited to processing this amount in increments under $100,000.00. Can this be changed?

If I remember correctly, the 420 allows clerk and cashier log on so try programming a clerk code. Make sure you don't program all of the clerks or cashiers or you may lock yourself out of programming. Just play with cashier or clerk 1 to test it. Otherwise, try printing out the cashier and clerk programs and it should show you what the current codes are

Some older POS registers and almost all manual credit card readers inside at the cashier allow manual entry. However, no manual entry allowed at the gas pump.

-Worked as a cashier at a gas station for 10+ years

It is easy to know if you have logged on a cashier correctly. After entering the cashier, you will see hyphens around the cashier number on the display. For example, if you sign on as cashier 1, you will then see -01- on the display. If not, you haven't logged on and you will get a longer beep when you try to use department buttons which means please log on.

It sounds like an entry limit has been set. This is often called HALO (high amount lock out) in many manuals. Look in your programming manual to see if there is a limit function. If you need a programming manual, one of the users has most of them here:
https://the-checkout-tech.com/

NOT ASSIGNED means no cashier is signed on. Find the cashier number button, probably labeled CASH #. In REG mode, press CL to clear the error, then 1, then CASH #, and Cashier 1 will be assigned. The display will show -01- Go straight from here into your sale.
Some registers are set up to not show the cashier number on the display or receipt. If 1 CASH # doesn't work, try CASH #, 1, CASH #.
Most users don't track sales by cashiers, so they forget they even have the capability, and they forget how to use that CASH # key. If you press the CASH # button without entering a number, it will sign out the active cashier, and you'll get this NOT ASSIGNED error.

Each department in the register can be programed with a maximum price. Sharp calls it a HALO, for High Amount Lock-Out, and it prevents those silly mistakes like a cashier once made for me when my burger and shake came out to over $500.00.
If you're entering a reasonable price, but the register complains that it is OVER LIMIT, you need to program a higher HALO for that department. Look for the department programming in the manual.

When printer performs it cleans print head nozzles to avoid clogging,in this process its splits the ink in service station, when its reaches beyond the limit ink comes out.
Open service station soak in to warm water clean entire enk dry it then fix it back, or else replace service station.

The WLAN light will normally blink if there is data passing through. Most often if the problem is that you need a reboot for the router to work again you will need to update the firmware of your router. You need to go to www.linksys.com then click on the top right search then look for your model number then select the option to WRT54G downloads. Search for your model and then download the firmware. After that on a computer wired to your router go to http://192.168.1.1 through Internet Explorer. Click on the administration tab then click Choose. Select the file that you downloaded then click on Upgrade. That should fix your problem.

When people call in they more than likely hit a Call Routing Application eventually. You would have to assign the greeting to the Day and/or Night greeting in order for it to play.