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Replying to:
bmcowboy
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Re: Optiplex 9010 SFF - 3 monitor issue, followed Dell's ste

Hi @gandaio1 ,

I know how it feel, bro, co'z I've got similar experience with frustration before on some ThinkVision + ThinkPad. Here's something from WiKi that may help in your case while it DID solve mine!

"...Ivy Bridge
HD 2500 and HD 4000 GPUs in Ivy Bridge CPUs are advertised as supporting three active monitors, but many users have found that this does not work for them due to the chipsets only supporting two active monitors in many common configurations. The reason for this is that the chipsets only include two phase-locked loops (PLLs); a PLL generates a pixel clock at a certain frequency which is used to sync the timings of data being transferred between the GPU and displays.

Therefore, three simultaneously active monitors can only be achieved by a hardware configuration that requires only two unique pixel clocks, such as:

  • Using two or three DisplayPort connections, as they require only a single pixel clock for all connections. Passive adapters from DisplayPort to some other connector rely on the chipset being able to emit a non-DisplayPort signal through the DisplayPort connector, and thus do not count as a DisplayPort connection. Active adapters that contain additional logic to convert the DisplayPort signal to some other format count as a DisplayPort connection.
  • By using two non-DisplayPort connections of the same connection type (for example, two HDMI connections) and the same clock frequency (like when connected to two identical monitors at the same resolution), so that a single unique pixel clock can be shared between both connections.
  • Using the Embedded DisplayPort on a mobile CPU along with any two other outputs."

Despite your Dell monitor on VGA, let's check out the 2 Lenovo ThinkVision:

LT2452P

  • Clock frequency: 205MHz
  • Horizontal addressability: 1920 pixels (max)
  • Vertical addressability: 1200 lines (max)

L2251x (page #23)

  • Clock frequency: 205MHz
  • Horizontal addressability: 1680 pixels (max)
  • Vertical addressability: 1050 lines (max)

Voilà! You got it now, right? Yes! The 2 different ThinkVision occupied 2 unique pixel clocks already and thus no rooms for the third connection (VGA). It also explained why 2 displays in your case always works no matter if DP#1+VGA or DP#2+VGA or DP#1+DP#2.

Just a short test: Try connect 2 identical ThinkVison to the 2 DP ports and the Dell monitor on VGA, then see if it do the tricks. Good luck, dude!

 

“May the Force be with Dell.”
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