JVC KM-F250: Difference between revisions

Revision as of 01:56, 7 February 2026

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 13.5 MHz, 8-bit 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, and analog component (Y/R-Y/B-Y) video inputs. A loopthrough reference sync (black burst/genlock) input is provided for synchronizing output timing to external equipment, along with a dedicated DOC (dropout compensator) RF carrier input for use with VTRs that provide an RF output. The unit provides two composite video outputs, component outputs, Y/C separate outputs, and three sync reference outputs (ADV SYNC for VTR servo lock, REF SYNC composite sync, and REF BB black burst).

The unit includes comprehensive proc amp controls behind the front panel: video (Y) level, chroma level, U-V balance, and setup level — each with a variable/unity switch allowing ±3 dB adjustment (±10% for setup). An H position control allows output horizontal timing adjustment within ±7 µsec, and a Y/C timing control adjusts chroma-to-luminance phase within ±1 µsec. A chroma advance switch advances the chroma output by 1H with respect to luminance when enabled. All front-panel controls can be disabled via a LOCAL/REMOTE switch when using the optional RM-P250 remote control unit.

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 with significant differences in Y/C signal handling:

KM-F250U — NTSC variant for the US market (120V, 60Hz). Y/C uses separate BNC connectors for luminance and chrominance. Supports Y/C at 3.58 MHz (S-VHS NTSC) and 688 kHz (U-matic DUB).^[1]^[2]
KM-F250E — European PAL variant (100–240V, 50/60Hz). Y/C uses a 7-pin DIN connector (with included 7P-to-BNC adapter cable). Supports Y/C 443 at 4.43 MHz (PAL S-VHS), Y/C 924 at 924 kHz (hi-band U-VCR), and Y/C 629 at 629 kHz (VHS). Output Y/C format is selectable via a rear-panel switch (443/924/629), while input Y/C format is set via an internal select pin.^[3]
KM-F250EG — European PAL variant (230V, 50Hz)

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 S-VHS, VHS, U-matic, and other formats.

Internally, the KM-F250 comprises ten circuit boards: RL (relay/bypass switching), CN (connector interface), MT (mounting/interconnect), VIDEO (analog signal processing), MEMORY (digital TBC/frame memory with A/D and D/A conversion), SG (sync generator/SSG), PS (switching power supply producing +12V, −12V, and +5V), REG (voltage regulator converting ±12V to ±9V for video circuits), SUB (subsidiary functions), and PB DET (playback detection).^[3]

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.

Photos

Signal Specifications

The following input/output specifications are derived from the JVC KM-F250 user manual (NTSC model)^[4] and the KM-F250E service manual (PAL model).^[3]

Input Signals

Signal	NTSC Model (U)	PAL Model (E/EG)	Impedance
Composite (VBS)	1.0 Vp-p	1.0 Vp-p	75 Ω
Y (luminance)	1.0 Vp-p (with sync)	0.7V + 0.3V sync (Y/C 443) or 0.35V + 0.15V sync (Y/C 924/629)	75 Ω
S-chroma	3.58 MHz, 0.286 Vp-p (burst)	4.43 MHz, 0.3 Vp-p (burst)	75 Ω
U-chroma (U-matic DUB)	688 kHz, 0.50 Vp-p	924 kHz, 1.0 Vp-p (VBS)	75 Ω
C (VHS)	—	629 kHz, 1.0 Vp-p (VBS)	75 Ω
Component Y	0.7V + 0.3V sync	0.7V + 0.3V sync	75 Ω
Component R-Y	0.7 Vp-p (100%) / 0.525 Vp-p (75%)	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%)	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	Black burst 0.45 Vp-p or PAL-B composite 1.0 Vp-p	75 Ω (loopthrough)
DOC RF carrier	0.2–1.0 Vp-p (3–10 MHz)	0.2–1.0 Vp-p (3–10 MHz)	75 Ω

Output Signals

Signal	NTSC Model (U)	PAL Model (E/EG)	Impedance
Composite (VBS) × 2	1.0 Vp-p	1.0 Vp-p	75 Ω
Y (luminance)	1.0 Vp-p (with sync)	0.7V + 0.3V sync (443) or 0.35V + 0.15V sync (924/629)	75 Ω
S-chroma	3.58 MHz, 0.286 Vp-p (burst)	4.43 MHz, 0.3 Vp-p (burst)	75 Ω
U-chroma (U-matic DUB)	688 kHz, 0.85 Vp-p	924 kHz, 0.5 Vp-p	NTSC: 390 Ω / PAL: 75 Ω
C (VHS)	—	629 kHz, 0.5 Vp-p	75 Ω
Component Y	1.0 Vp-p (with sync)	0.7V + 0.3V sync	75 Ω
Component R-Y/B-Y	0.7 Vp-p (100%) / 0.525 Vp-p (75%)	0.7 Vp-p (100%) / 0.525 Vp-p (75%)	75 Ω
ADV SYNC	—	4 Vp-p (advanced 8H)	75 Ω
REF SYNC	—	4 Vp-p	75 Ω
REF BB	—	0.45 Vp-p	75 Ω

Note: On NTSC models, Y/C signals use separate BNC connectors for luminance and chrominance. On PAL models (E/EG), Y/C input and output use a combined 7-pin DIN connector with an included 7P-to-BNC adapter cable. The Y/C input format on PAL models is set via an internal select pin (Y/C 443, Y/C 924, or Y/C 629); the output format is selectable via the Y/C OUTPUT switch behind the front panel.

Performance Specifications

The following performance measurements are from the KM-F250E service manual.^[3]

Parameter	Composite	Component	Y/C Separate
S/N ratio	57 dB (p-p/RMS, 100 kHz – 5 MHz)
Residual jitter	±15 nsec	±15 nsec	Luminance ±15 nsec, hue ±3°
K Factor (2T Pulse)	3%	1%	1%
Frequency response	3.2 MHz, ±0.5 dB	Y: 5.2 MHz, ±0.5 dB; R-Y/B-Y: 2.2 MHz, ±0.5 dB	Y: 5.2 MHz, ±0.5 dB; C: 500 kHz, ±3 dB

Ambient operating temperature: −5 to 40°C (23 to 104°F).

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.^[5]

The PS (power supply) circuit board uses a switching regulator to produce +12V, −12V, and +5V DC rails. The REG (regulator) board then converts the ±12V rails to ±9V for the video processing circuits. Failure of any rail can prevent the digital processing circuitry from functioning while bypass mode (which routes signals through the RL board's analog switching circuit) continues to pass video normally.^[3]

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.^[5]

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.
↑ ^3.0 ^3.1 ^3.2 ^3.3 ^3.4 Document:JVC KM-F250E Service Manual — JVC service manual No. 6455 for the KM-F250E. Contains circuit descriptions, adjustment procedures, exploded views, parts lists, and schematic diagrams.
↑ JVC KM-F250 User Manual (English) — hosted by Adcom S.r.l. Original manufacturer documentation covering signal specifications, operating procedures, and adjustment trimmers.
↑ ^5.0 ^5.1 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.

[bcs-listing-1] BroadcastStore.com — "JVC KM-F250U TBC &/or Frame Synchronizer" — US broadcast equipment dealer listing confirming KM-F250U model designation.

[reddit-kmf250u-2] 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.

[service-manual-3] 3.0 ^3.1 ^3.2 ^3.3 ^3.4 Document:JVC KM-F250E Service Manual — JVC service manual No. 6455 for the KM-F250E. Contains circuit descriptions, adjustment procedures, exploded views, parts lists, and schematic diagrams.

[manual-specs-4] JVC KM-F250 User Manual (English) — hosted by Adcom S.r.l. Original manufacturer documentation covering signal specifications, operating procedures, and adjustment trimmers.

[videohelp-psu-5] 5.0 ^5.1 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.

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@@ Line 6: / Line 6: @@
 |images=JVC KM-F250U rear.webp,JVC KM-F250U boards.webp
 |power_avg=40
-|weight=6.9 kg (15.2 lbs)
+|weight=6.9 kg
 |features=Full-frame time base correction, frame synchronization, dropout compensation (DOC), field freeze and frame freeze, multi-format signal/standard transcoding, genlock via external reference input, CCIR Rec. 601 (4:2:2) processing at 13.5 MHz 8-bit quantization, RS-170A compliant (NTSC models), 1 MB frame memory, proc amp controls (video level, chroma level, U-V balance, setup level — each switchable variable/unity), H position adjustment (±7 µsec), Y/C timing adjustment (±1 µsec), optional RM-P250 remote control unit, EIA 19" rack mountable
 |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 13.5 MHz, 8-bit 4:2:2 sampling, effectively making it a multi-purpose TBC suitable for professional video production and archival workflows.