Direct answer
For the Sony X85K 4K TV, protocol support, same-network discovery, guest isolation and protected-content restrictions should be separated. First, place both devices on the primary network and test photos or the home screen.
What this covers
- Sony X85K 4K TV (KD-43/50/55/65/75/85X85K)
- Sony BRAVIA TV; Google TV/Android TV version, XR processor, panel and HDMI 2.1 ports vary.
- The specific fault this record addresses: will not AirPlay, Cast or screen mirror
What it does not cover
- ×The same symptom on a different Sony product line, which has its own record and its own cited source
- ×An on-screen error code whose meaning has not been checked against this exact model's manual
- ×Live electrical, gas, sealed-system, internal battery-cell or structural repair — a technician boundary, not a self-service step
Differential
What actually causes this, and how to tell them apart
These are ordered by how often each one is the answer, not by how easy it is to try. The point of the middle column is that two causes producing the same headline symptom rarely produce the same detail — that detail is what tells you which one you have before you change anything.
- 1
The devices are on different networks
What separates it Nothing appears in the cast or AirPlay list, with the phone on a guest network or a separate band the set is not on.
How to confirm Guest networks are the most common cause. Both devices must be on the same network, and on some routers the 2.4 GHz and 5 GHz bands are treated as separate segments.
- 2
Client isolation is enabled on the router
What separates it Both devices are demonstrably on the same network and still cannot see each other.
How to confirm Client or AP isolation prevents devices on the network communicating with each other. It is commonly on by default on guest networks and some mesh systems.
- 3
AirPlay or the casting feature is disabled on the set
What separates it The television does not appear as a target at all, and the feature is off in its settings.
How to confirm It is a separate setting that is not always enabled by default.
- 4
A VPN on the phone is blocking local discovery
What separates it Discovery stopped working after a VPN was installed or enabled.
How to confirm Many VPNs route local network traffic away from the local segment. Disable it for one test.
- 5
The content is copy protected
What separates it Everything mirrors except one streaming app, which shows a black screen or an error.
How to confirm Many streaming services deliberately block mirroring. Use the app on the television itself instead — this is intended behaviour, not a fault.
- 6
The set's software is out of date
What separates it AirPlay or Cast stopped after a phone operating-system update.
How to confirm Protocol changes on the phone side can require a corresponding television update. See software-update.
Before you touch a setting
Record this first — changing settings destroys the evidence
Every item below stops existing the moment a reset, re-pair or settings change is made. Written down first, they are what separates the causes above; recovered afterwards, they are guesswork.
- Whether both devices are on exactly the same network, including the same band where the router separates them.
- Whether the phone is on a guest network.
- Whether a VPN is active on the phone.
- Whether the failure affects everything or only one streaming app.
Put both devices on the same network, avoiding any guest network
ReversibleThis is the most common cause, and on some routers the 2.4 GHz and 5 GHz bands count as separate segments.
Disable any VPN on the phone for one test
ReversibleMany VPNs route local discovery traffic away from the local network entirely.
Confirm AirPlay or casting is enabled in the television's settings
ReversibleIt is a separate setting and is not always on by default.
Check for client or AP isolation on the router
ReversibleIt stops devices on the same network from seeing each other and is often on by default for guest networks.
Use the app on the television itself for protected content
ReversibleMany streaming services deliberately block mirroring, and that is intended behaviour rather than a fault.
Model-specific
What is true of this model and not of its siblings
Generic advice for the product line fails here. Each item below is a property of this specific model family that changes which of the steps above apply to you.
- Model scope
- KD-43/50/55/65/75/85X85K. Sony BRAVIA TV; Google TV/Android TV version, XR processor, panel and HDMI 2.1 ports vary.
- Panel — LED LCD, native 120Hz
- 2022 LED LCD with a native 120 Hz panel and the X1 processor (not the higher Cognitive Processor XR). A backlight with limited local dimming, so blacks are less deep and blooming more visible than XR/Mini-LED models; that is the tier, not a fault.
- Smart platform
- Google TV. Update at Settings › System › About › System software update; Chromecast built-in and AirPlay 2.
- Dolby Vision — yes
- Supports Dolby Vision, HDR10 and HLG — unlike Samsung.
- Gaming / HDMI
- Two HDMI 2.1 ports for 4K 120 Hz; it is one of Sony's more affordable 120 Hz panels. Put the console on an HDMI 2.1 port (the higher-numbered ones) and enable the game/enhanced format for that input.
- Symptom boundary
- This record covers Sony X85K 4K TV when it will not AirPlay, Cast or screen mirror. A different symptom on the same hardware, or this symptom on a different Sony product line, has its own record with its own causes and its own cited source.
Stop boundary
When this stops being a self-service repair
Continuing past any one of these costs more than the repair saves — in safety, in warranty, or in evidence a technician needs.
- !Do not disable router security features permanently to enable mirroring; client isolation exists for a reason on shared and guest networks.
Evidence ledger
Sources behind this answer
Visible sources support the visible claims. Home Product Support records the publisher, the fact used and the review date; community reports can suggest an issue but do not become a published fact on their own.
Where the manufacturer's article stops. Sony Support publishes this as "Television and computer support". Official Sony and BRAVIA manuals, firmware and troubleshooting support. What that article does not carry is the model boundary — it is written for a product line, and KD-43/50/55/65/75/85X85K is the scope applied here. Where a control label, terminal, indicator pattern or reset sequence differs on your unit, the manual for that exact model is the authority, not this page and not the article.
Exact questions
Common follow-ups
Does the Sony X85K support 4K 120Hz gaming?+
Yes — the X85K has a native 120 Hz panel and two HDMI 2.1 ports that do 4K 120 Hz, which is unusual at its price. Connect the console to one of the HDMI 2.1 inputs, use a certified Ultra High Speed cable, and turn on the enhanced/HDMI format for that input so it accepts the higher-bandwidth signal.
My phone can't see the TV to cast to it.+
Check that both are on exactly the same network, and specifically that the phone is not on a guest network — that is the most common cause by a distance. On some routers the 2.4 GHz and 5 GHz bands are also treated as separate segments, so a phone on one and a television on the other cannot discover each other.
Everything mirrors except one streaming app, which shows a black screen.+
That is deliberate. Many streaming services block screen mirroring for copyright reasons, and a black screen with audio, or an error, is the expected result rather than a fault. Use that service's own app on the television instead.
Does this answer apply to every Sony model?+
No. It is scoped to KD-43/50/55/65/75/85X85K. Sony BRAVIA TV; Google TV/Android TV version, XR processor, panel and HDMI 2.1 ports vary.
What should I record before troubleshooting AirPlay or Cast or mirroring?+
Record the complete model identifier, exact message or indicator, software/firmware where visible, the operating stage and what still works.
Why is a factory reset not the first step?+
A reset can erase accounts, networks, maps, schedules or preferences without distinguishing AirPlay, Cast, mirroring. The ordered checks preserve that evidence.
When should I stop and use qualified service?+
Do not bypass protected content or weaken network security.
Answer for the exact device and software version shown above.