Heavy magenta colour cast on L25500 60 inch

Hello, it's my first time on this forum, thanks in advance for helping me. I have a problem with a HP L25500 latex plotter that shows a heavy magenta colour cast; the problem occours randomly and a different level of intensity. Sometimes I obtain acceptable printing, sometimes everything looks heavily magenta. When I print the "printhead test plot", it shows a magenta square instead of the yellow one as shown in the attachment file. Is this normal? I don't think so. The strange thing is that if I print a Yellow linear gradient, everything seems good and Yellow! A few months ago I replaced the carriage PCA with a new one to solve some printhead not recognized issues as suggested from a local hp technician. Now I have this new issue with the magenta that is driving me crazy and reading some forum I found out that is probably the carriage PCA again; is this possible that I could have bought a damaged carriage PCA? Is the carriage PCA the only thing that could cause this problem? I think that is a electronic problem since it occours randomly and at different intensity. Is there any test to do to understand the cause of the problem? I don't want to spend a lot of money try to find the right solution, replacing working hardware without understanding the real problem. Thank You for helping me!