Mx3123 user manuel - New Home MX-3123 Computerized Sewing Machine

https://www.manualslib.com/manual/921948/Janome-Myexcel-23x-Mx3123.html?page=11#manual

the left side head of the machine opens up to expose the bulb.

Even the best of machines vary depending on how they are being used. Certain machines are better at embroidery, while others are better for sewing garments or home projects. Decide what you want to do with your machine, test them out, and then decided which is best for YOU!!!

...

Perhaps this manual will help:

Janome Myexcel 23X MX3123 Instruction Book

Mostly it happens when tensioner is to tight. Try letting off tension a little at the time.

try this link for a manual and parts
http://www.sewingpartsonline.com/Janome-3123-Sewing-Machine-Parts.aspx

you can contact janome customer service & ask them about the
oiling or I've providing a link for a manual to see if the oiling information
is in the manual

http://www.sew4less.com/product/560/Janome_and_New_Home_MX3123_Instruction_Manual

sound like it needs to be serviced

1/28/13 - I have Janome Harmony 2049 that was initially sewing forward with no reverse and then after about 12 inches of sewing would ONLY sew in reverse. After spending an hour getting the plastic housing off...I was able to locate the shaft that made the reverse. It needed lubrication and after working it in and unjamming the part from the down position, the forward and reverse now work!
Huh, right? Hope it continues to work well. It is a smooth running machine, otherwise. Good luck!

go to www.ifixmachines.com

http://safemanuals.com/user-guide-instructions-owner-manual/SINGER/QUANTUM%209940-_E

Click on Download the complete user guide (9002 Ko)
from right side of the window