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Discuss BENQ Blur Reduction (strobe backlight) and the Blur Busters Strobe Utility. For Z-Series monitors (V2 firmware) on XL2411Z, XL2420Z and XL2720Z.


Postby rky » 23 Dec 2014, 06:14

Hello. I recently purchased this monitor so I was very excited when I saw this blur blusters application was endorsed and available for the v2 edition. All I want to know is how muchpotential risk does this program pose to damaging my monitor even if I stick within the thresholds?

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Postby Falkentyne » 23 Dec 2014, 11:56

No risks at all. The utility is only a "front end" to communicate with the monitor's strobe settings, without having to use the service menu. The service menu has the same adjustments, although you can enable strobing adjustments without enabling single strobe, if you use the service menu (but if you have single strobe off, you will need to change the brightness one notch, or change strobe duty or strobe phase, for the custom duty/phase settings to be 'active" if you go from disabled blur reduction to enabled (from OSD). (seems to be a bug; that's why the windows utility enables single strobe whenever any adjustment is made).

Double strobe was designed for 50-75 hz refresh rates. All refresh rates higher than 75hz single strobe automatically. Single strobe "on"
is for 60-75hz (do NOT use it at 50 hz!!)

You asked about safe adjustments?
Ok, when NOT using vertical total tweaks (VT tweaks), **ALL** strobe duty and strobe phase changes are 100% safe (except at 50hz), even strobe phase up to 100 and single strobe at 60hz. However the windows utility values shown are based on the VT 1350/1500 tweak being active-that's why the slider shows a 0.5ms (strobe duty 003) to 5 ms (duty 030) range.

The actual values and ranges you truly get, WITHOUT a VT tweak, are shown on this website:
(go down to the backlight pulse width paragraph).

With VT tweaks, do not exceed strobe phase 059 for 100hz or 049 for 120hz, when adjusting through the service menu (see masterotaku's massive thread about how strobe phase can affect the strobe duty when using tweaks). The windows utility is limited to strobe phase 047 for safety.

Safe strobe duty settings?
000-030 are 100% safe at every refresh rate when NOT using VT tweaks (except 50hz has a bug where single strobe fails to strobe at all and just overdrives the monitor brightness voltages. I believe this bug occurred because the original V1 firmware was designed to ALWAYS double strobe at 50-75hz, while V2 had an option to single strobe at 60-75 hz. it seems like Benq forgot to include 50hz pulse widths. OOPS!, so ONLY use DOUBLE STROBE at 50hz. Single strobe could *damage the backlight* if the OSD brightness is higher than 30 !!!!).

When using VT tweaks, you need to remember some simple things.

WITHOUT VT tweaks, 60hz refresh rate has a persistence range of 0.07ms (strobe duty 001) to 5 ms (duty 030), in 30 step values (corresponding to the strobe duty), so 006 duty=1 ms, 012=2 ms, 018=3 ms, 024=4ms and 030 (max)=5 ms. This is tested and safe by design.

120hz refreshes the screen twice as fast as 60hz, so, by common simple logic, the persistence values will be cut in HALF (darker screen, smoother motion) since the monitor is refreshing twice as fast. So 120hz is rated for HALF the persistence values: 0.08 to 2.5ms (half of .17 and 5ms)

100hz is similar but close: 0.1 ms at strobe duty 001 to 3ms at duty 030.

Why is this important?
Well, for some reason (neither chief or strobemaster fully explained *why*, however), when using VT tweaks (1350 or 1500/1502 vertical total), the monitor switches to the (60hz) backlight pulse widths, instead of the pulse widths for your current refresh rate! So if you are using 120hz with a VT 1500 tweak, it will use the 60hz persistence values (this is why the OSD shows 60hz when using a VT tweak, btw). I think you can already see the problem.

120hz is rated for 2.5ms persistence maximum, but 60hz is rated for 5ms. But when using the VT tweak, 120hz uses the 60hz values, so the max value becomes 5 ms instead of 2.5ms! (so strobe duty 001 becomes .17ms instead of 0.08ms, and strobe duty 030 becomes 5 ms instead of 2.5ms). So if you go above strobe duty 015 (2.5ms), with VT tweak, you can *potentially* shorten the life of the LED's because you are driving them at a current beyond what they are rated for.
This is untested and unproven, as the LED's CAN handle 5ms pulses, but only validated at 60hz refresh rate, so just use common sense.
There's no benefit to going above 2ms persistence, anyway (not only does it make the motion blur reduction have less effect, it also lowers the position of the top crosstalk strobe pulse settling error, farther down the top of the screen, so its always best to use the lowest strobe duty you can keep decent brightness with (UNLESS you are not using a VT tweak, then you need to balance duty and phase to keep the center of the screen (or maybe the top in FPS games) as ghost free as possible :)

So to be fully in compliance, do not exceed 015 strobe duty (2.5ms) for 120hz, and 018 strobe duty (3ms) for 100hz, when using a VT tweak. that's all you need to remember.

And when using a VT tweak, going beyond 059 strobe phase at 100hz and 49 strobe phase at 120hz will drop the persistence to (0 ms), which will shut off the backlight (obviously). if that ever happens, use the S-switch or the customized hotkey to turn off blur reduction (strobe settings are only for BBR ON, not for off), reduce the strobe phase, then re-enable.
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Postby rky » 23 Dec 2014, 19:47

That was a marvelously in-depth response with crystal clarity. Thank you very very much.
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Postby etegv » 30 Dec 2014, 17:58

How can I turn single strobe on? Where are these options? I have the xl2411z v2 firmware

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Joined: 25 Feb 2014, 19:26


Postby TE5LA » 23 Feb 2016, 20:00

I have a late-model XL2420Z from Amazon too, pretty sure it's v2, but the Strobe Utility just crashes when I try to run it. Also, the instructions about accessing a service menu do not work on mine.
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Joined: 22 Feb 2016, 19:40


Postby Falkentyne » 23 Feb 2016, 22:54

They work on all of the monitors, without any exceptions whatsoever.

Unlocking the service and factory (burn-in) menu may not work after an "AC" power off. The monitor must first be powered on then turned off with the power button.
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