Fault
ZX7 Stick Welding Spark But No Arc: A5 Voltage and Driver Board Checks
A WelderData fault route for ZX7 stick welding cases where a spark appears but the machine does not sustain an arc.
Database summary
“Spark but no arc” in stick welding is different from a completely dead output. The machine may show a small spark or weak ignition attempt but fail to sustain welding current. The ZX7 service route uses main-circuit confirmation, control-board A5 voltage comparison and driver-board U1 voltage evidence to split the fault.
A5 voltage split: driver board or control board?
The ZX7 reference pattern uses the voltage between A5 pin 3 and A5 pin 4 as a service split. In no-load condition the reference is treated as zero. With the output shorted under controlled service conditions, a reading above about 4V points toward a driver-board fault, while a value below about 1V points toward a main control-board fault.
| Check point | Observed value | WelderData route |
|---|---|---|
| A5(3) to A5(4), no-load | 0 reference | Baseline check before short-output diagnosis. |
| A5(3) to A5(4), controlled short-output test | > 4V | Driver-board fault route. |
| A5(3) to A5(4), controlled short-output test | < 1V | Main control-board fault route. |
Use this split only after connectors, main circuit devices and wiring are confirmed. Do not short output terminals without qualified service setup and current control.
Driver board U1 voltage check
For the driver-board route, U1 pin 13 relative to connector P1 pin 3 is expected to be above about 5.3V in the reference pattern. If the reading is below about 5V, the related resistor chain should be checked, including R11 10K, R10 5.1K and R9 750Ω.
This check is useful because it gives a board-level path after the symptom “spark but no arc.” It avoids replacing IGBTs or control boards before the driver-board evidence has been separated.
Before using the A5 / U1 path
- Confirm the control-board connectors are installed correctly.
- Confirm the main power devices and output rectifier path are not obviously damaged.
- Confirm mode switches and front-panel controls are in the expected SMAW / stick state.
- Confirm output leads, ground connection and welding cable condition.
- Use a current-limited and qualified service setup for any output-short test.