Disconnect the SigCon cable at both ends. Using a known-good short coaxial jumper, connect the display’s sync output directly to its sync input (if the radar has a loopback mode). If the error disappears, the cable or slip ring is faulty.
The sync detection circuit on the processor board (e.g., main digital PCB) may be damaged.
Symptoms: Sync signal present at input connector (verified with oscilloscope) but error persists.
Fix:
The multi-core cable between scanner and display carries:
Symptoms: Antenna rotates normally, but no sweep on screen or “NO SYNC”.
Fix:
1. [Power on radar] → Transmit ON.
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2. Antenna rotates?
NO → Check scanner motor, fuse, belt.
YES ↓
3. Any radar video at all?
NO → Check magnetron (unrelated but can mimic sync loss).
YES ↓
4. Image is rolling/spoking?
YES → Suspect sync signal loss.
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5. Access service menu (JRC: typically hold [Menu] + [Enter] at power-up).
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6. View diagnostic → Look for "Trigger OK?" or "Heading pulse count."
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7. Trigger = NO → Test cable continuity for trigger line.
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8. Cable OK → Likely scanner trigger board failure.
