Brother International T-8420B Instruction Manual - English - Page 42

10. TROUBLESHOOTING Problem 6 Uneven seam Possible cause y Is the presser foot pressure too weak? Adjust the presser foot pressure. y Is the feed dog too low? Adjust the feed dog height. y Is the bobbin scratched? If the bobbin is damaged, smooth it with an oiled grindstone or replace it. y Is the V-belt tension too low? Adjust so that there is 10-14 mm of deflection in the V-belt 2948M when it is pushed with a finger. 7 Large degree of puckering y Is the upper thread tension too strong? (excess tension) Make the upper thread tension as weak as possible. y Is the lower thread tension too strong? Make the lower thread tension as weak as possible. y Are the thread take-up spring tensions too strong? Make the thread take-up spring tension as weak as possible. y Is the thread take-up spring operating range too large? Move the stopper to as high a position as possible. y Is the presser foot pressure too strong? Adjust the presser foot pressure. y Is the thread take-up amount too small? 2949M Adjust the thread take-up amount. 8 Material slippage y Is the presser foot pressure too strong? Adjust the presser foot pressure. 2949M Page 26 * 7 25 25 * * 26 27 26 2950M 9 Lower thread is tangled at y Is the bobbin spinning direction correct when the lower thread is the sewing start. being pulled? Set the bobbin so that it turns in the opposite direction to the rotary hook. y Is there too much thread Lower thread wound onto the bobbin? The bobbin winding amount should not be more that 80 %. y Is the bobbin turning smoothly? If the bobbin is not turning smoothly, replace the bobbin. y Is a bobbin other that the light-alloy bobbins specified by Brother being used? Use only bobbins which are specified by Brother. 2951M 2124M 17-18 16 17-18 T-8420B, 8450B, 8720B, 8750B 36