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I have an old IBM monitor here and I'd like to use it as a second screen to my computer (Mac mini running Fedora or Thinkpad running Archlinux). I plugged it into the electricity socket without a computer connection once and turned it on. It made the typical old monitor static noise and nothing exploded. Still, I am not sure if it is safe to connect it to a newer computer.

The monitor itself

Connection cables

The label

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That's an IBM PS/1 monitor. The large DB connector is used to give supply to the computer (which has not a power supply of itself). The monitor is VGA capable, so as long as you connect it to a VGA adapter and set it to 640x480 @60Hz, you are fine. The monitor can go down to 50Hz, and possible, up to 72Hz.

  • Alright. How do I go about setting the values you named? – Merlin Feb 23 '17 at 7:40
  • Does the computer automatically adjust the values to the capability of the monitor? I'm kinda afraid of what will happen if it tries to go beyond those values by default. Is there any risk of danger? – Merlin Feb 23 '17 at 8:11
  • This monitor, AFAR, doesn´t give any data thru the DB15 cable, so the only information the computer may receive from it is that it is a colour monitor. You would have to go to the Control Panel of your OS and set the mode yourself. – mcleod_ideafix Feb 23 '17 at 11:14
  • Not sure about that particular monitor, but it will either tell you something along the lines of "signal over range" or just show a blank screen. This is not going to damage anything inside. – Algimantas Feb 23 '17 at 11:16
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    @Merlin, automatic capability detection is almost certain to fail for this monitor: it uses the old monitor ID pin signalling system, while virtually everything from the past 25 years expects DDC -- you'll need to set the resolution and refresh rate manually. The monitor probably doesn't have any protection circuits, but driving it at too high a resolution or refresh rate probably won't damage it -- it's too-low frequencies that are usually a problem. – Mark Feb 23 '17 at 21:14
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If your Mac Mini is from 2009 or later, it will have two video output connectors: Mini-DVI and Mini DisplayPort, or HDMI and Mini DisplayPort, or HDMI and Thunderbolt, or 2x Thunderbolt. Any of these ports except HDMI can output VGA with a simple adapter.

My ThinkPad (Lenovo W510) has a built-in VGA connector, and I've done dualscreen in Windows 7.

Once the monitor is physically connected, you just have to go into your OS' display settings and configure it for 640x480 60Hz. If your monitor supports higher resolutions and/or refresh rates, you can try different combinations until you find one that doesn't make your eyes tired or give you headaches.

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    A monitor from 1992 could well pre-date the widespread usage of "signal out of range" protection circuits. – Mark Feb 23 '17 at 21:00
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    @Mark: A properly-designed monitor from that era should not be damaged by out-of-frequency signals. Immunity from damage doesn't generally require out-of-range protection circuit as such. Fixed-frequency parts (e.g. VGA horizontal) should have an oscillator that will retrigger when the amount of time since the last cycle exceeds a duration slightly longer than the nominal period, or when a sync pulse is active and the time since the last cycle exceeds a duration slightly shorter than a nominal period. If the durations are set to values the circuitry can tolerate, the monitor... – supercat Feb 23 '17 at 22:09
  • ...won't be particularly stressed by sync pulses it receives. Variable-frequency parts are a bit more complicated, but have a part whose voltage is increased a bit when an incoming sync pulse is received and reduced when they generate a scan. The voltage will control the frequency of scanning, and will stabilize when the frequencies match. Since circuits to raise and lower the voltage can't drive beyond the supply rails, setting component values the voltage-to-frequency converter produces a tolerable frequency for all voltages within the supply rails will prevent damage. – supercat Feb 23 '17 at 22:13
  • @Mark: When the range of scan rates increased, digital control circuitry became more practical than analog circuitry, but all an analog monitor would have to do to protect damage from errant sync rates is choose component values that limit how much effect the incoming sync signals can have on its scanning behavior. – supercat Feb 23 '17 at 22:17
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    HDMI to VGA adapters, while not exactly simple (they have to include video DACs) are fairly inexpensive and may cost less than proprietary plain cables - think I paid around $5 for the one I got to use an old VGA-only LCD with a raspberry pi. – Chris Stratton Mar 2 '17 at 17:02

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