When the design calls for needles 11-15, the needle will set up off center and we get an error message. We have to manually adjust these needle to center. Needle 15 does not work at all as when it is called the machine moves to its far limit, shakes and vibrates before giving an error message. 

Once you have that cover removed, on the left hand side of the color change assembly you will find the Potentiometer, it is black in color or it may be royal blue and yellow, (depends on the machine)l. It is this component that we will adjust so your machine behaves correctly on color change.
 
The trick of setting the potentiometer is simply this. We must make sure that the potentiometer is synchronized with whatever needle is currently over the needle plate hole. In other words we must make the electronic component match the mechanical information currently set on our machine.
 
First make sure you are in the C/C Settings windows of your control panel, To do this follow this instruction:
 
Power on the machine, and as soon as your machine starts to make the series of beeping tones on the power up, you need to press the IN/OUT and the SETTINGS button at the same time  Doing this correctly will bring us to the VERSION INSTALL screen on your control panel.
 
Once you see the VERSION INSTALL screen appear use your green arrow buttons to go to the option C/C SETTINGS. And then press SET, the information on that screen will be a diplay of the needle number that should reflect the needle that is lined up over the needle plate and a half turn sensor indicating ON. Yours will most likely say OFF which would be the incorrect setting and is why we will need to tweak the potentiometer so that the half turn sensor lines up correctly.
 
Remove the potentiometer from the half turn sensor which looks like a silver hat. You do this by loosening the one set screw that is deeper set into the half turn mechanism. There are 3 set screws, two lie on the surface of that silver hat, and there is one that is deeper set into the silver hat or half turn mechanism, only loosen the one deeper set,
 
After you've loosened that set screw slide the potentiometer out, Now turn the manual color change knob which is located behind the head and to the right. Now turn that so that you are between neeldes 14 and 15. In other words over the needle plate hole is no needle but it is between needle 14 and 15. Now turn the shaft of the potentiometer slowly until the screen on the machine reads (NEEDLE 14) then start to turn slowly so that it JUST changes to 15, The number should be flickering back and forth between needle 14 and 15. When you see this then turn the shaft back in the other direction just 1/8th of a turn. Use the groove at the apex of the shaft to determine the 1/8th of a turn.
  
Once completed gently insert the shaft back into the half turn sensor, being careful not to rotate the shaft upon insertion into the half turn sensor, now tigtn the small set screw that secures the potentiometer to the machine. Then turn the color change dial  so that needle 15 lines up over the needle plate, When turning that dial you'll notice that when the needle is over the needle plate, as your turning that dial you should feel that there is an area when turning that dial that there is no restriction in turning the dial like you feel when the head transitions side to side, It is like a free play area of the dial. If you know what I am referring to set needle 15 over the needle plate and then slowly turn the dial until you are at the middle of that free play area. Now look at the control panel display it should read;
  
  Needle: 15    Half Turn Sensor: On
  
If it does then rotate the dial the other direction to needle 14, make sure you get into the free play area of the dial so that needle 14 is directly over the needle plate hole and you are at the center of that free play area of the dial, The control panel should display:
  
  Needle: 14      Half Turn Sensor: On
  
Continue to do this all the way to needle 1, and then when you see needle one say Needle 1 and half turn sensor ON then exit out of the C/C Settings by pressing the PREVIOUS button and then scroll down to EXIT using the green arrow buttons and then press SET.
  
Now press the Number 2 on the control panel to see if the machine goes to needle 2, and then upon completion of that transition press number 3 to go to needle 3 and so on all the way to needle 15, then go from needle 15 to 8 (the middle needle) and then from 8 to 1, then 1 to 15.
  
After you have proven that everything is moving correctly, go ahead and put the covers back on the machines color change components. Make sure that you watch the very thin wires to the rear of the potentiometer when putting the cover back on. These wires are for the half turn sensor, and if the cover pulls or pinches those wires then you will get the symptoms that you are experiencing now, erratic recognizition of the needle that is over the needle plate, weird color change and chronic error 300's etc... If you feel that your issue that you are experiencing today is due to thise wires possibly being pulled or pinched after you went ahead and replaced the covers to the machine after you initially installed the potentiometer, let me know. If your machine test good on color change with the covers off but becomes erratic after you mount the covers, then it would be indicative that the half turn sensor wires have been damaged and they will need to be replaced.