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No picture through HDBaseT extender

very common

“Source is powered up, the TV says no signal, and the little black boxes at each end are just blinking at me.”

Likely causes

  • Twisted-pair link never came up: dead power-over-HDBaseT end, or one pair open or split in the run

    ~30%

    Link LED at the receiver is dark or blinking rather than steady. If the extender happens to provide LAN passthrough, a laptop on that port gets nothing either, which confirms it, but plenty of extenders have no LAN port at all, in which case the link LED is your whole answer.

  • HDMI side fault at one end: no hot plug detect, dead jumper, source on the wrong output

    ~25%

    Link LED is solid and steady, so the pair is fine, yet the source reports no display connected at all.

  • 4K60 4:4:4 exceeds what the extender generation can carry: a silicon ceiling, not a cable fault

    ~20%

    Force the source to 1080p60 or 4K30 and the picture comes straight up, stable. Push it back to 4K60 4:4:4 and it dies again, repeatably, and it does that on a perfectly certified channel. HDBaseT 2.0 tops out well below the roughly 18 Gbps an HDMI 2.0 source emits at 4K60 4:4:4, so that format passes only as 4:2:0, only vendor-compressed, or not at all. HDBaseT 3.0 raises the ceiling but is a different silicon generation. Read the extender's stated maximum video format off its own spec sheet before you blame the copper.

  • EDID: extender serves a default EDID the sink can't display, or the sink's EDID never reaches the source

    ~12%

    Direct-connected, source to display, it works. Through the extender the source's display list shows a generic monitor name or the switcher's model instead of the display.

  • HDCP authentication failing across the link

    ~8%

    Laptop desktop and menus show fine; the moment protected content plays it goes black or throws an HDCP message. Unprotected passes, protected does not.

  • Channel longer, or more patched, than the extender allows

    ~5%

    Intermittent: comes up after two or three power cycles, then drops. Add up run length plus every patch point and compare against the extender's own rating; class and maximum vary by manufacturer, so pull the model's spec sheet rather than assuming 100 m.

What to bring

  • extender manual or spec sheet
  • certification tester (Cat 6/6A, HDBaseT limit if available)
  • known-good certified HDMI cords
  • short factory patch cord
  • laptop
  • EDID reader or manager
  • HDMI test pattern generator if available

Steps

  1. Read the link and HDMI LEDs at both ends against the manual

    LED codes are manufacturer-specific. Do not guess them. You are answering one question: is the twisted-pair link up, yes or no. That single answer splits this fault in half and costs nothing.

    If that doesn’t do it

    Link down: go to the permanent link and power. Link up: go to the HDMI ends, the format and EDID.

  2. Cold power-cycle in order: display, receiver, transmitter, source

    Pull power, do not use standby. Ten seconds off the display. Handshake state machines latch on a bad negotiation and stay latched. A clean sequenced restart recovers a real share of these before you touch a tool.

    If that doesn’t do it

    It returned but comes back later: EDID or HDCP management. It never came back: keep going.

  3. Swap both HDMI jumpers for known-good certified cords

    Free, sixty seconds, and short jumpers are the single most-replaced part in AV. Certified Premium High Speed for 18 Gbps, Ultra High Speed for 48 Gbps. Anything unbranded in a 4K path is a suspect, not a control.

    If that doesn’t do it

    No change: leave the good cords in and move on.

  4. Force the source resolution down

    Set the source to 1080p60, or 4K30 / 4K60 4:2:0. 4K60 4:4:4 is roughly 18 Gbps; 4:2:0 or 30 Hz roughly halves that. A picture at the lower rate tells you the channel is intact and the format is the problem: either it is above this extender generation's video ceiling, or it is eating the channel's last margin. Those are different fixes, so find out which before you order anything.

    If that doesn’t do it

    Dead at every resolution: the path is broken, not marginal.

  5. Bench the extender pair beside the source

    Transmitter and receiver side by side on a short factory patch cord. Working here moves the fault into the permanent link. Still dead here and the fault is the hardware, the format, EDID or HDCP, and you just saved yourself a trip up the ladder.

    If that doesn’t do it

    Works on the bench: certify the installed link. Fails on the bench: check the format against the extender's rating, then swap the pair.

  6. Certify the permanent link, and read the margins, not just PASS

    Test NEXT, return loss and length against Cat 6/6A limits per ANSI/TIA-568.2, and run your tester's HDBaseT or extended-frequency video limit if it has one. HDBaseT is far less forgiving of return loss and alien crosstalk than 1000BASE-T, so a channel can PASS the data limit and still fail video. A continuity tester will happily pass a split pair HDBaseT will not tolerate. Where only the TIA limit is available, read the margin figures rather than the verdict: thin return-loss or NEXT margin on a channel that fails video is your evidence.

    If that doesn’t do it

    Link passes with healthy margin: the fault is the format, EDID, HDCP or the extender.

  7. Set a fixed EDID and verify HDCP version end to end

    Stop using pass-through. Lock the extender or matrix input to an EDID matching what the sink can actually display, and what the extender can actually carry. Then confirm every device in the chain supports the HDCP version the content demands; one older device blanks the leg.

    If that doesn’t do it

    Still dead with a good link, good cords, a supported format and managed EDID: replace the extender pair and retest.

References

  • HDBaseT Spec 2.0
  • HDBaseT Spec 3.0
  • HDMI 2.0b
  • HDMI 2.1
  • ANSI/TIA-568.2
  • VESA Enhanced EDID (E-EDID) Standard

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