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JVC KM-F250: Difference between revisions

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Add product photos (front, rear, boards) from Reddit r/VIDEOENGINEERING post (via update-page on MediaWiki MCP Server)
Major update from KM-F250E service manual: add power/weight/dimensions, 3 new sync outputs, fix composite output count to 2, add Performance Specifications section, note Y/C variant differences (7-pin DIN vs BNC, PAL vs NTSC frequencies), add PSU circuit detail, add remote control info (via update-page on MediaWiki MCP Server)
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|image_main=JVC KM-F250U front.webp
|image_main=JVC KM-F250U front.webp
|images=JVC KM-F250U rear.webp,JVC KM-F250U boards.webp
|images=JVC KM-F250U rear.webp,JVC KM-F250U boards.webp
|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, RS-170A compliant, 1 MB frame memory
|power_avg=40
|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.
|weight=6.9 kg (15.2 lbs)
|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.


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.
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).


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 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 KM-F250 was produced in several regional variants:
The unit features field freeze and frame freeze functions, useful for still-frame capture in production environments.
* '''KM-F250U''' — NTSC variant for the US market (120V, 60Hz)<ref name="bcs-listing">[https://www.broadcaststore.com/store/model_detail.cfm?id=7814 BroadcastStore.com — "JVC KM-F250U TBC &/or Frame Synchronizer"] — US broadcast equipment dealer listing confirming KM-F250U model designation.</ref><ref name="reddit-kmf250u">[https://www.reddit.com/r/VIDEOENGINEERING/comments/1erdlcu/my_jvc_kmf250_frame_synchronizertime_base/ 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.</ref>
 
* '''KM-F250E''' — European PAL variant (230V, 50Hz), with NTSC 4.43 output capability
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).<ref name="bcs-listing">[https://www.broadcaststore.com/store/model_detail.cfm?id=7814 BroadcastStore.com — "JVC KM-F250U TBC &/or Frame Synchronizer"] — US broadcast equipment dealer listing confirming KM-F250U model designation.</ref><ref name="reddit-kmf250u">[https://www.reddit.com/r/VIDEOENGINEERING/comments/1erdlcu/my_jvc_kmf250_frame_synchronizertime_base/ 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.</ref>
* '''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.<ref name="service-manual">[[: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.</ref>
* '''KM-F250EG''' — European PAL variant (230V, 50Hz)
* '''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 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.


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.
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).<ref name="service-manual" />
 
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.
|av_system=PAL,NTSC,NTSC 4.43
|av_system=PAL,NTSC,NTSC 4.43
|frequency=50Hz,60Hz
|frequency=50Hz,60Hz
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|type=Frame synchronizer
|type=Frame synchronizer
|buffer_size=1 MB (full frame)
|buffer_size=1 MB (full frame)
|notes=Full-frame TBC conforming to CCIR Rec. 601 (4:2:2). Processes both luminance and chrominance signals.
|notes=Full-frame TBC conforming to CCIR Rec. 601, 13.5 MHz 8-bit 4:2:2 quantization. TBC range: 625 H (PAL) / 525 H (NTSC). S/N ratio: 57 dB (p-p/RMS, 100 kHz – 5 MHz). Residual jitter: ±15 nsec (composite/component), ±15 nsec luminance + ±3° hue (Y/C).
}}
}}


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|audio=None
|audio=None
|location=rear
|location=rear
|notes=Luminance (Y) input, 1.0 Vp-p, 75 ohms. Shared between S-VHS (3.58 MHz) and U-matic DUB (688 kHz) Y/C modes.
|notes=Luminance (Y) input, 1.0 Vp-p, 75 ohms. On NTSC models, shared BNC between S-VHS (3.58 MHz) and U-matic DUB (688 kHz) Y/C modes. On PAL models (E/EG), Y/C uses a 7-pin DIN connector instead of separate BNCs.
}}
}}


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|audio=None
|audio=None
|location=rear
|location=rear
|notes=S-VHS chrominance input at 3.58 MHz subcarrier, 0.286 Vp-p (burst level), 75 ohms.
|notes=S-VHS chrominance input. NTSC models: 3.58 MHz, 0.286 Vp-p (burst level), 75 ohms. PAL models (E/EG): 4.43 MHz, 0.3 Vp-p (burst level), 75 ohms. On PAL models this signal is carried via the 7-pin DIN Y/C connector rather than a separate BNC.
}}
}}


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|audio=None
|audio=None
|location=rear
|location=rear
|notes=U-matic DUB chrominance input at 688 kHz color-under frequency, 0.50 Vp-p, 75 ohms.
|notes=U-matic/VHS chrominance input. NTSC models: 688 kHz (U-matic DUB), 0.50 Vp-p, 75 ohms. PAL models (E/EG): switchable between 924 kHz (hi-band U-VCR, C = 1.0 Vp-p VBS) and 629 kHz (VHS, C = 1.0 Vp-p VBS) via internal select pin. On PAL models this signal is carried via the 7-pin DIN Y/C connector.
}}
}}


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|audio=None
|audio=None
|location=rear
|location=rear
|notes=Analog component Y/R-Y/B-Y input. Y: 1.0 Vp-p, 75 ohms; R-Y and B-Y: 0.7 Vp-p at 100% color bars (0.525 Vp-p at 75%), 75 ohms.
|notes=Analog component Y/R-Y/B-Y input. Y: 0.7V video + 0.3V sync (1.0 Vp-p total), 75 ohms; R-Y and B-Y: 0.7 Vp-p at 100% colour bars (0.525 Vp-p at 75%), 75 ohms.
}}
}}


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|signal=Composite (CVBS)
|signal=Composite (CVBS)
|connector=BNC
|connector=BNC
|count=1
|count=2
|audio=None
|audio=None
|location=rear
|location=rear
|notes=Black burst (0.45 Vp-p) or composite sync (1.0 Vp-p) reference input with loopthrough output for genlock synchronization.
|notes=Black burst (0.45 Vp-p) or composite video (1.0 Vp-p) reference input. Two BNC connectors — one serves as loopthrough output. Unused connector should be terminated with 75-ohm plug (included).
}}
}}


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|audio=None
|audio=None
|location=rear
|location=rear
|notes=Dropout compensator RF carrier input, 3–10 MHz, 0.2–1.0 Vp-p, 75 ohms. Used with VTRs that provide an RF output for dropout detection.
|notes=Dropout compensator RF carrier input, 3–10 MHz, 0.2–1.0 Vp-p, 75 ohms. Connect to VTR's reproduced RF signal output (DOC OUT). Do not connect to TV output RF converter.
}}
}}


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|signal=Composite (CVBS)
|signal=Composite (CVBS)
|connector=BNC
|connector=BNC
|count=1
|count=2
|location=rear
|location=rear
|notes=Composite video (VBS) output, 1.0 Vp-p, 75 ohms.
|notes=Composite video (VBS) output, 1.0 Vp-p, 75 ohms. Two independent BNC outputs (COMP VIDEO -1 and -2), active simultaneously in Operate mode.
}}
}}


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|count=1
|count=1
|location=rear
|location=rear
|notes=Luminance (Y) output, 1.0 Vp-p, 75 ohms. Shared between S-VHS and U-matic DUB output modes.
|notes=Luminance (Y) output, 75 ohms. NTSC models: 1.0 Vp-p, shared BNC between S-VHS and U-matic DUB modes. PAL models (E/EG): 0.7V video + 0.3V sync (443 mode) or 0.35V + 0.15V sync (924/629 modes), via 7-pin DIN connector.
}}
}}


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|count=1
|count=1
|location=rear
|location=rear
|notes=S-VHS chrominance output at 3.58 MHz subcarrier, 0.286 Vp-p (burst level), 75 ohms.
|notes=S-VHS chrominance output. NTSC models: 3.58 MHz, 0.286 Vp-p (burst level), 75 ohms. PAL models (E/EG): 4.43 MHz, 0.3 Vp-p (burst level), 75 ohms, via 7-pin DIN connector. Output format selectable via Y/C OUTPUT switch.
}}
}}


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|count=1
|count=1
|location=rear
|location=rear
|notes=U-matic DUB chrominance output at 688 kHz color-under frequency, 0.85 Vp-p, 390 ohms.
|notes=U-matic/VHS chrominance output. NTSC models: 688 kHz, 0.85 Vp-p, 390 ohms. PAL models (E/EG): switchable between 924 kHz (0.5 Vp-p, 75 ohms) and 629 kHz (0.5 Vp-p, 75 ohms) via Y/C OUTPUT switch, via 7-pin DIN connector.
}}
}}


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|count=1
|count=1
|location=rear
|location=rear
|notes=Analog component Y/R-Y/B-Y output. Y: 1.0 Vp-p, 75 ohms.
|notes=Analog component Y/R-Y/B-Y output. Y: 0.7V video + 0.3V sync, 75 ohms; R-Y/B-Y: 0.7 Vp-p (100% colour bars), 0.525 Vp-p (75%), 75 ohms.
}}
 
{{AV output
|label=ADV SYNC
|output_type=Video
|signal=Composite (CVBS)
|connector=BNC
|count=1
|location=rear
|notes=VTR servo lock signal output, 4 Vp-p, 75 ohms. Advanced by 8H with respect to REF outputs (internally switchable to 4H). Connect to playback VTR external sync input for time code editing.
}}
 
{{AV output
|label=REF SYNC
|output_type=Video
|signal=Composite (CVBS)
|connector=BNC
|count=1
|location=rear
|notes=Reference composite sync output from internal SSG, 4 Vp-p, 75 ohms. For genlocking downstream equipment to the KM-F250's timing reference.
}}
 
{{AV output
|label=REF BB
|output_type=Video
|signal=Composite (CVBS)
|connector=BNC
|count=1
|location=rear
|notes=Reference black burst output from internal SSG, 0.45 Vp-p, 75 ohms. For genlocking downstream equipment to the KM-F250's timing reference.
}}
}}


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== Signal Specifications ==
== Signal Specifications ==


The following specifications are derived from the JVC KM-F250 user manual.<ref name="manual-specs">[https://www.adcom.it/public/images/Manual/KM-F250%20MAN%20ENG.pdf JVC KM-F250 User Manual (English)] — hosted by Adcom S.r.l. Original manufacturer documentation covering signal specifications, operating procedures, and adjustment trimmers.</ref>
The following input/output specifications are derived from the JVC KM-F250 user manual (NTSC model)<ref name="manual-specs">[https://www.adcom.it/public/images/Manual/KM-F250%20MAN%20ENG.pdf JVC KM-F250 User Manual (English)] — hosted by Adcom S.r.l. Original manufacturer documentation covering signal specifications, operating procedures, and adjustment trimmers.</ref> and the KM-F250E service manual (PAL model).<ref name="service-manual" />


=== Input Signals ===
=== Input Signals ===
{| class="wikitable"
{| class="wikitable"
! Signal !! Level !! Impedance
! Signal !! NTSC Model (U) !! PAL Model (E/EG) !! Impedance
|-
| Composite (VBS) || 1.0 Vp-p || 1.0 Vp-p || 75 Ω
|-
|-
| Composite (VBS) || 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
|-
|-
| Y (shared Y/C) || 1.0 Vp-p (with sync) || 75 Ω
| S-chroma || 3.58 MHz, 0.286 Vp-p (burst) || 4.43 MHz, 0.3 Vp-p (burst) || 75 Ω
|-
|-
| U-chroma (688 kHz) || 0.50 Vp-p || 75 Ω
| U-chroma (U-matic DUB) || 688 kHz, 0.50 Vp-p || 924 kHz, 1.0 Vp-p (VBS) || 75 Ω
|-
|-
| S-chroma (3.58 MHz) || 0.286 Vp-p (burst level) || 75 Ω
| C (VHS) || — || 629 kHz, 1.0 Vp-p (VBS) || 75 Ω
|-
|-
| Component Y || 1.0 Vp-p (with sync) || 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%) || 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%) || 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 || 75 Ω (loopthrough)
| 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) || 75 Ω
| 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 ===
=== Output Signals ===
{| class="wikitable"
{| class="wikitable"
! Signal !! Level !! Impedance
! 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
|-
|-
| Composite (VBS) || 1.0 Vp-p || 75 Ω
| C (VHS) || — || 629 kHz, 0.5 Vp-p || 75 Ω
|-
|-
| Y (shared Y/C) || 1.0 Vp-p (with sync) || 75 Ω
| Component Y || 1.0 Vp-p (with sync) || 0.7V + 0.3V sync || 75 Ω
|-
|-
| U-chroma (688 kHz) || 0.85 Vp-p || 390 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
|-
|-
| S-chroma (3.58 MHz) || 0.286 Vp-p (burst level) || 75 Ω
| ADV SYNC || — || 4 Vp-p (advanced 8H) || 75 Ω
|-
|-
| Component Y || 1.0 Vp-p (with sync) || 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.<ref name="service-manual" />
{| class="wikitable"
! Parameter !! Composite !! Component !! Y/C Separate
|-
| S/N ratio || colspan="3" | 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 ==
== 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.<ref name="videohelp-psu">[https://forum.videohelp.com/threads/402345-JVC-KM-F250-TBC-no-output 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.</ref>
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.<ref name="videohelp-psu">[https://forum.videohelp.com/threads/402345-JVC-KM-F250-TBC-no-output 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.</ref>
 
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.<ref name="service-manual" />


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.<ref name="videohelp-psu" />
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.<ref name="videohelp-psu" />

Revision as of 01:52, 7 February 2026

JVC KM-F250
AV device › Frame synchronizer
Overview
Brand
JVC
Model
KM-F250
Type
Frame synchronizer
AV system
PAL, NTSC, NTSC 4.43
ECID
EC3408
Inputs
Rear
Y/C In (S-VHS)
1×S-Video (Y/C) (Hirose 7-pin DUB)
S-VHS Y/C input mode, selected via Y/C INPUT switch behind front panel. Y = 1.0 Vp-p with sync, C = 0.286 Vp-p (burst level) at 3.58 MHz, 75 ohms. Connect to 7-pin Y/C output of S-VHS VTR.
Y/C In (U-VCR)
1×Y/C DUB color-under (Hirose 7-pin DUB)
U-matic DUB input mode, selected via Y/C INPUT switch behind front panel. Y = 1.0 Vp-p with sync, C = 0.50 Vp-p at 688 kHz, 75 ohms. Connect to DUB output of 3/4" U-format VCR.
Component In
1×Component (YPbPr) (BNC)
Analog component Y/R-Y/B-Y input via three BNC connectors. Y: 0.7V video + 0.3V sync (1.0 Vp-p total), 75 ohms; R-Y and B-Y: 0.7 Vp-p at 100% colour bars (0.486 Vp-p at 75%), 75 ohms.
DOC
1×RF (BNC)
Dropout compensator RF carrier input, 3–10 MHz, 0.2–1.0 Vp-p, 75 ohms. Connect to VTR's reproduced RF signal output (DOC OUT). Do not connect to TV output RF converter.
Composite In
1×Composite (CVBS) (BNC)
Composite video (VBS) input, 1.0 Vp-p, 75 ohms.
GENLOCK
1×Composite (CVBS) (BNC)
Black burst (0.45 Vp-p) or composite video (1.0 Vp-p) reference input. Two BNC connectors configured as loopthrough. Unused connector should be terminated with 75-ohm plug (included).
Outputs
Rear
Composite Out
2×Composite (CVBS) (BNC)
Composite video (VBS) output, 1.0 Vp-p, 75 ohms. Two independent BNC outputs, active simultaneously in Operate mode.
REF SYNC
1×Composite (CVBS) (BNC)
Reference composite sync output from internal SSG, 4 Vp-p, 75 ohms. For genlocking downstream equipment to the KM-F250's timing reference.
Y/C Out (U-VCR)
1×Y/C DUB color-under (Hirose 7-pin DUB)
U-matic DUB output mode, selected via Y/C OUTPUT switch behind front panel. Y = 1.0 Vp-p with sync, C = 0.85 Vp-p at 688 kHz, 390 ohms. Connect to DUB input of 3/4" U-format VCR.
REF BB
1×Composite (CVBS) (BNC)
Reference black burst output from internal SSG, 0.45 Vp-p, 75 ohms. For genlocking downstream equipment to the KM-F250's timing reference.
ADV SYNC
1×Composite (CVBS) (BNC)
VTR servo lock signal output, 4 Vp-p, 75 ohms. Advanced by 8H with respect to REF outputs (internally switchable to 4H). Connect to playback VTR external sync input for time code editing.
Y/C Out (S-VHS)
1×S-Video (Y/C) (Hirose 7-pin DUB)
S-VHS Y/C output mode, selected via Y/C OUTPUT switch behind front panel. Y = 1.0 Vp-p with sync, C = 0.286 Vp-p (burst level) at 3.58 MHz, 75 ohms. Connect to 7-pin Y/C input of S-VHS VTR.
REF SC
1×Composite (CVBS) (BNC)
Reference color subcarrier output from internal SSG, 1 Vp-p, 75 ohms. For genlocking downstream equipment. Note: Do not connect to VTR SC input terminal; this output is not for feeding subcarrier back to VTRs.
Component Out
1×Component (YPbPr) (BNC)
Analog component Y/R-Y/B-Y output via three BNC connectors. Y: 1.0 Vp-p (with sync), 75 ohms; R-Y/B-Y: 0.7 Vp-p (100% colour bars), 0.486 Vp-p (75%), 75 ohms.
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
Dimensions
Weight
15.212 lb6.9 kg <br /> / 6.9 kg15.212 lb <br />
Power
Voltage
220–240V 100–120V
AC frequency
50Hz, 60Hz
Power
40W
Time Base Correction
Type
Frame synchronizer
Buffer
1 MB (full frame)
Notes
Full-frame TBC conforming to CCIR Rec. 601, 13.5 MHz 8-bit 4:2:2 quantization. TBC range: 625 H (PAL) / 525 H (NTSC). S/N ratio: 57 dB (p-p/RMS, 100 kHz – 5 MHz). Residual jitter: ±15 nsec (composite/component), ±15 nsec luminance + ±3° hue (Y/C).
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"kg(15.2lbs)" is not declared as a valid unit of measurement for this property.

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]

See Also

References

  1. ↑ BroadcastStore.com — "JVC KM-F250U TBC &/or Frame Synchronizer" — US broadcast equipment dealer listing confirming KM-F250U model designation.
  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.
  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.
  4. ↑ JVC KM-F250 User Manual (English) — hosted by Adcom S.r.l. Original manufacturer documentation covering signal specifications, operating procedures, and adjustment trimmers.
  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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