These hard-to-find transistors are used to regulate the voltage to the print head. If these go bad, then you will gradually notice extreme deflection, significant missing nozzles and eventually an entire color missing. Since bad transistors exhibit the same results with clogged dampers and electrically bad heads, you will have to go through a whole suite of tests to determine where the problem lies.
In most Roland head and main boards, there are fuses to check first before checking the transistors. For JV3 and JV4 boards, there are no fuses and the transistors will be the first to blow.
Each print head utilizes 2 different transistors. This part number is for the transistor labeled C4131 If you are not familiar with testing NPN transistors, you will need to consult an electronics technician or learn the testing methods through the internet. We do not provide technical information on testing these.
Should you need help in replacements or servicing your board, we provide such repair services - please look on this page for this.