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Interesting problem

B

Bladestorm

[H]ard|Gawd
Joined
Dec 10, 2006
Messages
1,232
I've had the monitor and (most of) the computer in my signature working fine together for the last two years. I just built a 2nd PC, and hooked it up to the monitors 2nd DVI input. Long story short, through some troubleshooting I found out that the monitor lets a small amount of electricity to travel from the first PC through DVI 1 into DVI 2 out to my 2nd computer. Enough electricity to run the case and GPU fans while the system is not even plugged into an outlet.

In other words, I have the first PC powered on and connected to DVI 1 on the monitor. I have ONLY the DVI cable plugged into the 2nd PC. I go to hook it up to DVI 2 on the monitor and the case and GPU fans start spinning. Not very fast, but they are spinning. I turn off the monitor and unplug it, the fans still spin. I unplug the DVI cable from DVI 1, and the fans stop.

The only thing I can think of is either my monitors circuitry is faulty, or somethings wrong with the first PC? Any ideas?
 
Power is sent over HDMI leads and different power sources must be isolated.
The spec states on pin 18, the max current is 0.05A @ 5V which translates to 0.25W, so pretty low power.

When 2 PCs are connected to a monitor, power is being delivered from 2 different PCs graphics cards/PSUs.
2 Power sources at the same voltage are not really at the same voltage, they will have a DC offset and a much smaller varying AC component that will not match.
Both power supplies will see each other as a load and will fight each other to maintain what each sees as the correct voltage.
This can easily exceed the 0.05A rating for HDMI and in an extreme case could pose a fire hazard.

It is the monitors task to isolate both voltage supplies so they dont compete with each other and so one PSU doesnt drive the 2nds circuits when the 2nd PSU is switched off.
The grounds may all be common, but the voltage supplies should be isolated.
Can you try another monitor to see if the same happens?
 
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