Brother International TU-878B Instruction Manual - English and Spanish - Page 120

15. TROUBLESHOOTING GUIDE 15. FEHLERSUCHE 15. RECHERCHES DE PANNES 15. GUIA PARA LA LOCALIZACION DE FALLAS Problem 4. Skipped stitches occur while sewing Where to check ¡ Is the needle tip bent? Is the needle tip blunt? If the needle tip is bent or broken, replace the needle. ¡ Is the needle properly installed? If it is incorrect, install the needle correctly. ¡ Is the machine properly threaded? If it is incorrect, thread the thread correctly. ¡ Is the sewing speed too fast? Check whether the correct motor pulley (with the correct outer diameter) that matches the maximum sewing speed and frequency of your particular model and sewing specifications is being used. If it is not correct, replace the motor pulley. * Depending on the type of material being used, skipped stitches may occur even when sewing at the maximum sewing speed within the rated range. In such cases, replace the motor pulley with a pulley which is one size smaller in diameter, or reduce the sewing speed. ¡ Is the upper feed timing incorrect? Adjust the walking foot, inner presser foot and needle timing. Page 24 24 29 - 33 8 Motor instruc- tion manual 66 5. Skipped stitches at sewing start Thread unravelling at sewing start ¡ Is the needle up stop position too high? (877B/878B) Adjust the synchronizer. ¡ Are the lower thread retainer springs pressing against the lower threads after thread trimming? (877B/878B) If the lower thread retainer springs are not pressing against the lower threads, adjust the positions of the movable knives. ¡ Is the height of the feed dog correct? Adjust so that the feed dog is 1 mm above the needle plate at its highest position. ¡ Are the thread take-up spring tensions too strong? Reduce the tension of the thread take-up springs. ¡ Are the ranges of movement for the thread take-up springs too large? Reduce the ranges of movement of the thread take-up springs. ¡ Are the trailing lengths of the upper threads too short after thread trimming? (877B/878B) Adjust the pretension. ¡ Are the threads not being trimmed cleanly? (877B/878B) Sharpen the fixed knives, or replace the fixed and movable knives if necessary. ¡ Is the needle too wide? Try using a needle with a count that is one lower than the current needle. ¡ Is the sewing speed too fast at the sewing start? (877B/878B) Use the slow start feature. 69 78 · 81 (Step 5-7) 56 52 51 43 76 24 Motor instruc- tion manual 6. Uneven seam ¡ Is the feed dog too low? Adjust the feed dog height. 56 ¡ Is the bobbin scratched? If the bobbin is damaged, smooth it with an oiled grindstone or re- - place it. ¡ Is the V-belt tension too low? Adjust so that there is 10 - 14 mm of deflection in the V-belt when it 14 is pushed with a finger. ¡ Is the upper feed timing incorrect? Adjust the walking foot, inner presser foot and needle timing. 66 101 SU-877A/B, TU-878A/B (English)