Help ! weird problem, black head and cyan head both firing at same time SP300

[damonCA21]

Have a strange problem on my SP300 - when I print or do a test print some nozzles on the black head are firing at the same time as the cyan. When I try and do a test print of a block of cyan, it has thin black lines going through it where some of the black nozzles are also firing at the same time the cyan one is ?
Anybody else had a problem like this ?
I have replaced the head cables to see if it helped and it didnt. Have done the normal manual and auto cleans in case it was just ink that had got on the cyan head, but it is definitely the black firing when the cyan is being told to

 

[Solventinkjet]

Does it look like the black is mixing into the cyan in the nozzle check by chance? If so, I'd start with some new dampers and make sure your maintenance tubes aren't clogged.

 

[damonCA21]

Thanks, no definitely isnt an ink mixing problem, this is the actual black nozzles firing

 

[damonCA21]

It isnt firing over the cyan and magenta head at all, only when trying to print cyan?

 

[damonCA21]

It looks almost like certain nozzles are just getting random signals to fire when they aren't meant to