Question 1

the projector keeps switching itself on randomly in the middle of the night. it's creepy and wasting lamp hours.

Accepted Answer

DIAGNOSIS The HDMI CEC and/or LAN Control features are turned on, and a signal from a connected device is waking it up. FIX Press the menu button on the remote. Go to System -> System Setup. Set HDMI Control to Off. Then, go to LAN Control and set it to Off as well. This severs the automatic wake-up signals. IF THAT DIDN'T WORK Check the Auto Power On setting in the same System menu. Ensure it's set to Off. Also, physically disconnect the HDMI cable from the projector when not in use to eliminate any phantom power signals. HEADS UP If you use a smart home system (like Control4) that integrated with the projector, turning off LAN Control will break that integration. You'll need to configure the system to not send spurious wake commands instead.

Question 2

there's a weird flickering or shimmering in bright areas of the picture, looks like fine moving dots. only in hdr mode.

Accepted Answer

DIAGNOSIS This is likely color dithering or noise from the HDR tone mapping process, exacerbated by certain sharpness or contrast settings. FIX Go to Picture -> Advanced Settings. First, reduce the Sharpness level. Set it between 0 and (at most) 3. Next, find the Gamma setting in HDR mode and change it from the default. Try Gamma 2.2 or Gamma 2.4 to see which reduces the noise. IF THAT DIDN'T WORK On your source device (e.g., Apple TV, PS5), try forcing the HDR output format. If it has a choice between HDR10 and Dolby Vision, force HDR10. The TH685P doesn't support Dolby Vision, and mismatched signaling can cause artifacts. HEADS UP Some inherent noise in very bright HDR highlights is normal for single-chip DLP projectors in this price range. It's less visible from your seating distance.

Question 3

the remote works super intermittently, have to point it directly at the lens and be super close. batteries are new.

Accepted Answer

DIAGNOSIS The IR receiver sensor on the projector is likely obstructed or has a very narrow reception angle. It's located right next to the front lens. FIX Remove any clear protective film you might have left on the projector's front face, especially around the lens. Ensure no physical objects, like a soundbar or a cable, are blocking the immediate area around the lens. IF THAT DIDN'T WORK The remote's IR emitter might be weak. Try using your smartphone camera to check the remote—point the remote at the phone camera and press a button; you should see a faint purple light through the phone screen. If not, the remote is faulty. HEADS UP The IR sensor on this model is notoriously finicky. For reliable control, consider using the BenQ Control app on your smartphone over WiFi, or get a universal remote that supports BenQ codes.

Question 4

the input lag feels higher than the advertised 8.3ms, especially in 60hz hdr mode. is there a setting i'm missing?

Accepted Answer

DIAGNOSIS You're likely not in the correct picture mode or have post-processing effects enabled that add latency. FIX Press the remote button that toggles picture modes. You must be in Game or User picture mode. In that mode's advanced settings, ensure BrilliantColor is set to 10 (it's fine for lag), but must turn OFF the following: Dynamic Black, Light Sense, Color Sense, and any noise reduction options. IF THAT DIDN'T WORK Check your source settings. On Xbox/PS5, ensure you're outputting at 1080p, not letting the console try to send a 4K signal that the projector then downscales (which adds lag). Also, use HDMI 2 port. HEADS UP The 8.3ms claim is for 1080p/60Hz in Game mode with HDR off. Enabling HDR adds a few milliseconds of processing latency—this is normal.

Question 5

how do i clean the filter on this thing? i can't find any info and it's getting dusty.

Accepted Answer

DIAGNOSIS The TH685P has a fixed, internal air filter that you cannot remove for cleaning. Dust is managed by the airflow system. FIX Use a can of compressed air. With the projector off and completely cool, hold it upright and gently blow air into the intake vent (on the side) and out through the exhaust vent. Do this in short bursts to dislodge dust without forcing it deeper. IF THAT DIDN'T WORK For heavy dust accumulation, you may need to open the case, which voids the warranty. If overheating persists due to dust, professional service is the safe option. HEADS UP Never use a vacuum cleaner directly on the vents. The static suction can damage internal components. Compressed air is the only recommended method.

Question 6

the hdmi signal keeps cutting out for a second then coming back, especially when my ps5 switches to hdr. using the included cable.

Accepted Answer

DIAGNOSIS This is an HDMI handshake issue. The projector and source are struggling to negotiate the HDR/4K signal format consistently. FIX First, bypass any intermediate devices like switches or receivers. Plug your PS5 directly into the projector's HDMI 2 port (it's the one with higher bandwidth). On the PS5, set the 4K Video Transfer Rate to -1 (instead of Automatic) and disable 120Hz output if you don't need it. IF THAT DIDN'T WORK Get a certified Ultra High Speed HDMI cable. The included cable is often mediocre. Also, on the projector, go to Display -> HDMI EDID and set it to 2.0 to force a stable standard. HEADS UP If you use an AVR, ensure it also fully supports HDMI 2.0/HDCP 2.2. Older receivers are a common bottleneck.

Question 7

why does my projector make a high-pitched whining or buzzing noise that changes when i go through menus? it's super annoying.

Accepted Answer

DIAGNOSIS That's coil whine from the power supply circuitry. It's a common physical trait in many electronics, not a defect, but it can be amplified by certain brightness/color settings. FIX Go into the Picture menu and change the BrilliantColor setting. Toggle it between Off, 1, 2, 3, 4, 5, and 10. One of these levels will significantly reduce or eliminate the noise. Usually, mid-levels like 3 or 4 are the quietest. IF THAT DIDN'T WORK Enable the Eco or SmartEco lamp mode. This lowers the lamp power, which often reduces the electrical load and the associated whine. HEADS UP The noise is most noticeable in a very quiet room and from close range. From your seating position with audio playing, it's often inaudible.

Question 8

my benq th685p just shows a solid red light on the power button and won't turn on at all, fan doesn't even spin.

Accepted Answer

DIAGNOSIS The projector is in a hard protection lockout, usually triggered by overheating or a power fault during its last shutdown. FIX Unplug the power cord from both the wall and the projector. Wait a full 5 minutes for internal capacitors to discharge. While it's unplugged, check the air intake and exhaust vents for any major dust blockage. Plug it back in directly to a wall outlet (not a power strip) and press the power button. IF THAT DIDN'T WORK The internal temperature sensor or power board might be faulty. Try a different, known-good power cable first. If no change, the unit likely needs service. HEADS UP Never move or unplug the projector immediately after turning it off. Always let the cooling fan run to completion, which can take a minute or two after the light goes off.

BenQ TH685P 1080p HDR Gaming Projector

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