Cyan Density Range Error & Insufficient Print Memory errors on M451nw

[printocoin]

Printer: LaserJet Pro M451nw

OS: Mac OS 10.15

My Cyan has been printing poorly for years (faded on the left side for about 5cms, then normal - see test page below). I replaced the Cyan cartridge and it did not resolve the issue.  I recently updated the firmware to the one dated 20190306. 

Since then, the printer has stopped being able to print, constantly showing "Insufficient Print Memory."

So, I have two issues:

1. The persistent Cyan printing problem (first image).

2. The "not being able to print anything" problem, which appears to be a memory issue caused by the recent firmware update using the HP Easy Start software. Screenshot of error reports attached here as the second image.

Thanks in advance for any help on either or both issues!

[Repairatrooper]

The fade on one site has 2 common causes. 

1. Bad cartridge, you can almost rule that out as the cause as you indicate that you tried 2 different cartridges, but depending on vendor you may have gotten 2 bad ones.

2. Issue with the HVPS (high voltage power supply) or the associated contacts that mate with the cartridge and apply the charge that attracts toner to the drum unit.

In some cases a defective cartridge in another slot can cause a voltage drop for other cartridges while working fine itself. Meaning you could have a bad yellow cartridge causing problems with cyan.

[printocoin]

Thanks for the quick response.

1. Yes, possible that it could be 2 bad cartridges. An HP repair guy is coming over so, hopefully he'll have a set of cartridges available for testing.

2. With respect to HVPS, is that part economic to replace? 

3. With regard to the Insufficient Print Memory, I am guessing that is a firmware problem - is there a way to downgrade firmware?

Many thanks in advance.