Start here — before replacing any parts
Err-08 means the sewing motor is blocked on the cited A4B-A-C controller; inspect a jammed sewing head and motor connection first.
Confirm your JACK A4B uses the A4B-A-C control-box edition; fault tables are not necessarily identical across controllers.
Manual scope: A4B-A-C control system only
Do these checks in order
Follow the steps below and keep a record of what changes after each one. Stop when an actual cause is confirmed.
Switch off and unplug the machine. Remove the workpiece and examine the needle, thread path, hook/bobbin area and accessible feed mechanism for tangled thread or a foreign object.
Only as the machine manual permits, check that the machine handwheel/head moves freely by hand with power disconnected; stop if there is hard resistance.
With power still disconnected, find the motor power connector at the matching A4B control system and check that it is fully seated and undamaged.
Reassemble guards, restore power and test slowly with no fabric. If Err-08 reappears immediately, record whether the head was free or blocked.
If the problem is gone
After removing a clear jam, the head runs normally and Err-08 stays cleared: do not buy a replacement motor.
If the problem is still there
Head remains stiff or code returns with no jam and good connector: mechanical binding, motor or controller needs qualified separation testing.
Which cause matches your result?
Use these more specific checks only when the earlier steps point to that possibility.
01Motor connector loose or a mechanical jam
Check the disconnected motor plug and inspect the head for trapped thread or other mechanical obstruction.
Remove the obstruction, securely reconnect the proper plug and restart. If Err-08 returns, ask the manufacturer to diagnose the controller.
How can I tell it is actually fixed?
Run a slow, unloaded test then a short scrap-fabric seam with the proper guards installed.
Before buying a replacement part
Confirm the A4B-A-C controller type, motor and connector before replacing any assembly.
Where this guidance comes from
Primary reference: View the manufacturer or manual reference ↗
Applicability: A4B-A-C control system only. Source evidence: Matching manufacturer manual; query demand not quantified.
The instructions are original English troubleshooting explanations derived from the listed technical facts; they are not a verbatim service manual. Do not apply them to an unverified revision.