Start here — before replacing any parts
Err-03 indicates input undervoltage on the referenced controller. Do not open the live control box to check it.
Confirm your JACK A4B uses the A4B-A-C control-box edition; fault tables are not necessarily identical across controllers.
Manual scope: 220V control box scope; licensed technician for voltage testing
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.
Confirm the installed control-box model and voltage rating; the cited reference concerns an AC220V control unit, which cannot be assumed to run from every US household outlet.
Unplug the machine and look for an obviously damaged cord, adapter or extension setup. Do not use a damaged cable or an improvised transformer.
Have a licensed electrician verify the supply and connections against the control-box nameplate under safe test procedures.
After the correct rated supply is restored, power on normally and observe whether Err-03 is cleared.
If the problem is gone
Err-03 disappears with a verified correct supply: the external undervoltage issue is likely resolved.
If the problem is still there
Rated supply tests correct but Err-03 remains: an authorized technician should diagnose control-box sensing and internal faults; do not bypass voltage protection.
Which cause matches your result?
Use these more specific checks only when the earlier steps point to that possibility.
01Supply input voltage is too low
Have a qualified person verify that mains voltage is in the specified range for the fitted controller.
Restore a suitable supply according to the controller rating; restart only when safe.
How can I tell it is actually fixed?
Restart at the rated voltage and perform a low-speed supervised stitching test.
Before buying a replacement part
Match the controller’s voltage variant and wiring harness exactly.
Where this guidance comes from
Primary reference: View the manufacturer or manual reference ↗
Applicability: 220V control box scope; licensed technician for voltage testing. Source evidence: Manufacturer manual confirmed; user search demand unquantified.
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.