JVC KM-F250
1×S-Video (Y/C) (Hirose 7-pin DUB)
1×Y/C DUB color-under (Hirose 7-pin DUB)
1×Component (YPbPr) (BNC)
1×RF (BNC)
1×Composite (CVBS) (BNC)
2×Composite (CVBS) (BNC)
1×Composite (CVBS) (BNC)
1×Y/C DUB color-under (Hirose 7-pin DUB)
1×Composite (CVBS) (BNC)
1×Composite (CVBS) (BNC)
1×S-Video (Y/C) (Hirose 7-pin DUB)
1×Composite (CVBS) (BNC)
1×Component (YPbPr) (BNC)
Description
The JVC KM-F250 is a professional rack-mountable frame synchronizer with integrated full-frame time base correction, originally marketed by JVC's Professional Products division. Though officially designated a "frame synchronizer," the unit performs full-frame TBC processing conforming to CCIR Recommendation 601 at 4:2:2 sampling, effectively making it a multi-purpose TBC suitable for professional video production and archival workflows.
The KM-F250 accepts composite (VBS), Y/C separate (both S-VHS at 3.58 MHz and U-matic DUB at 688 kHz), and analog component (Y/R-Y/B-Y) video inputs. The Y channel is shared between the U-matic and S-VHS Y/C modes via a common BNC connector. The unit also provides a loopthrough reference sync (black burst/genlock) input for synchronizing output timing to external equipment, and a dedicated DOC (dropout compensator) RF carrier input for use with VTRs that provide an RF output.
Output signals include composite, Y/C separate (both U-matic DUB and S-VHS formats), and component video. The unit features field freeze and frame freeze functions, useful for still-frame capture in production environments.
The KM-F250 was produced in several regional variants:
- KM-F250U — NTSC variant for the US market (120V, 60Hz)[1][2]
- KM-F250E — European PAL variant (230V, 50Hz), with NTSC 4.43 output capability
- KM-F250EG — European PAL variant (230V, 50Hz)
The "U" suffix follows JVC's standard professional product nomenclature for US-market models, consistent with their SA-T series TBCs (SA-T100U, SA-T300U, SA-T400U, etc.). The European variants accept PAL input and can output NTSC 4.43 (pseudo-NTSC with PAL subcarrier frequency), functioning as a basic standards transcoder. The unit was designed for use with consumer and semi-professional video systems including Betamax, VHS, U-matic, and other 1/2" formats.
The KM-F250 is relatively obscure compared to competing TBCs from FOR-A, DataVideo, and Snell & Wilcox, but is encountered in both US broadcast facilities and European archival environments. Common failure points include power supply degradation (the unit requires 5V, -5V, 12V, and -12V rails), which can cause a "low video level" indicator to illuminate with black output while the unit passes video normally in bypass mode.
Signal Specifications
The following specifications are derived from the JVC KM-F250 user manual.[3]
Input Signals
| Signal | Level | Impedance |
|---|---|---|
| Composite (VBS) | 1.0 Vp-p | 75 Ω |
| Y (shared Y/C) | 1.0 Vp-p (with sync) | 75 Ω |
| U-chroma (688 kHz) | 0.50 Vp-p | 75 Ω |
| S-chroma (3.58 MHz) | 0.286 Vp-p (burst level) | 75 Ω |
| Component Y | 1.0 Vp-p (with sync) | 75 Ω |
| Component R-Y | 0.7 Vp-p (100%) / 0.525 Vp-p (75%) | 75 Ω |
| Component B-Y | 0.7 Vp-p (100%) / 0.525 Vp-p (75%) | 75 Ω |
| Reference sync | Black burst 0.45 Vp-p or composite 1.0 Vp-p | 75 Ω (loopthrough) |
| DOC RF carrier | 0.2–1.0 Vp-p (3–10 MHz) | 75 Ω |
Output Signals
| Signal | Level | Impedance |
|---|---|---|
| Composite (VBS) | 1.0 Vp-p | 75 Ω |
| Y (shared Y/C) | 1.0 Vp-p (with sync) | 75 Ω |
| U-chroma (688 kHz) | 0.85 Vp-p | 390 Ω |
| S-chroma (3.58 MHz) | 0.286 Vp-p (burst level) | 75 Ω |
| Component Y | 1.0 Vp-p (with sync) | 75 Ω |
Known Issues
The most commonly reported failure mode is loss of video output when the unit is switched from bypass to operate mode. The front-panel "low video level" indicator illuminates and the output goes to black, while bypass mode passes video normally. Forum discussions indicate this is typically caused by power supply degradation — the unit requires 5V, −5V, 12V, and −12V rails, and failure of any rail can prevent the digital processing circuitry from functioning.[4]
The user manual (page 9) describes a video level adjustment trimmer, but users report this trimmer has no effect when the underlying issue is a power supply fault.[4]
See Also
References
- ↑ BroadcastStore.com — "JVC KM-F250U TBC &/or Frame Synchronizer" — US broadcast equipment dealer listing confirming KM-F250U model designation.
- ↑ Reddit r/VIDEOENGINEERING — "My JVC KM-F250 Frame Synchronizer/Time Base Corrector" — Owner photos of a KM-F250U unit showing front panel, rear I/O, and internal components.
- ↑ JVC KM-F250 User Manual (English) — hosted by Adcom S.r.l. Original manufacturer documentation covering signal specifications, operating procedures, and adjustment trimmers.
- ↑ 4.0 4.1 VideoHelp Forum — "JVC KM-F250 TBC no output" — Multiple users report identical symptoms (black output with "low video level" indicator in operate mode). Power supply voltage rail failure identified as likely cause.
