The HP Designjet CP series plotters were designed for the graphics market. They have high resolution (for there time, it was the best resolution available) 600dpi, and use bulk ink to refill the print heads between print jobs. The printer has many self-maintenance features, making it a very reliable printer. Missing print head pixels are detected and replaced with stand-by pixels without the user even knowing it happened. The CP series also have print head recovery procedure that almost always brings the print heads back to life.
They have automatic color calibration, humidity adjustment, internal diagnostics and lots of other features. The printer is well worth repairing. It was the Mercedes of its day. HP Designjet 2500CP and 3500CP repair parts can be purchased here. Free technical support is also available.