Aloka SSD-1400: no video signal on the BNC outputs
What happened
The video output died completely: no signal on the BNC connectors, and an oscilloscope on the coaxial cable showed silence.
What was checked
- Checked the video signal with an oscilloscope directly on the coaxial cable — nothing there.
- Cleaned the contacts with alcohol and re-seated the connectors — no change.
- Checked the backup battery; in the case as reported it read 3.9 V, so it was alive.
- Tried to identify the video board from the service manual — the part numbers did not match.
- Swapped every board into a known-good identical SSD-1400; all boards worked there.
- Then measured the power supply rails: the engineers found the ±15 V outputs missing and a blown fuse.
Cause
The power supply had failed: a blown fuse took out the ±15 V rails, so the video circuitry had no power. The boards themselves were fine — the dead supply simply looked like a dead video path.
What was done
Replaced the blown fuse and repaired the power supply; the ±15 V rails came back and the video output returned. The boards were reinstalled into the original unit.
Safety
Unplug the unit and let the PSU capacitors discharge before opening it — mains-side parts stay live; after any power supply repair, run earth-bond and leakage-current tests before returning the machine to use.
Lesson: Measure the supply rails before pulling boards — a missing voltage rail can look exactly like a dead video board, and a multimeter costs far less time than a full board swap.
Covered in the course: Ultrasound Service — Level 2: Fault-Finding →
Written from an anonymised case shared by service engineers. It is not a manufacturer instruction and grants no authorisation. Independent note; names are trademarks of their owners.