PC psu to power monitor

stree

stree

stree

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Advice required please.

I have a 30" TFT screen which is a one off, built as a prototype for someone at sometime, I got it through the bay and it has worked fine for a long time, however thr PSU has failed and the original manufacturer of the PSU wants £110 to repair/replace it.
I saw on "Hack a Day" site how someone had used an old PC psu to repair a flat screen with great results.
I have an old but good AT PSU and I intend to use this.
The monitor has an 8 pin DIN plug for power in labeled
PIN 124 return
PIN 35 +12volt
SHELL ground.
From this I assumed that return would be -12 volt, 12 volt would be 12 volt and ground would be ground.
But, opening the original monitor PSU to identify the wires by colour etc, I saw that the power cable has just one sheathed cable going to power in ( 12volt) but this was surrounded by braided steel like a coax, which was split and connected to both return and ground points on the PCB...
My question is, would it be OK to use the black ground cable from the AT PSU to act as both return and ground in this case?
 
I can't see it needing -12v. After a little reading I believe the negative 12v to be used for rs232 ports on a PC.

Return could simply be another word for common ground.

Surely if it were -12v it would say so as that'd be pretty important.

Wouldn't -12v and 12v make the monitor 24v?

I'd try just the 12v and ground first.
 
I will try to post pics later today, but its as simple as described, split braiding to ground and return solder points and 12 volt to another solder point,

Tealc, much as I was thinking, except why call it both ground and return? Unless the return circuit is via the earth, as in car electrics.
True though, if -12v was needed surely it would specify it.
Just dont want to fry it!

Thanks for your thoughts on this.
 
The shell could just be there for protection against interference and stuff and could be wired to the case of the PSU. The other returns could be physically wired to the PSU ground wires.

Without seeing the original PSU it would be hard to say for sure.
 
The shell on a DIN plug is always grounded. Just like USB has a ground pin and the shell is also grounded but they use the same wire. The naming is odd but it would be safe to assume that its 3,5 for +12v and the rest ground including the shell.

Even if this is wrong, you cant hurt a 24 volt device with 12v but you can hurt a 12v device with 24v ;)
 
Actually, that's not always true. With switching regulators, the lower the voltage the worse since the current increases to compensate (for a given load).
 
I will ignore the -12v, it seems to go against what is described and required.
I am inclined to the +12v and earth braid as ground and return
Now its a question of how to choose which wires from the PC PSU, I know yellow is +12v
and black is ground, but the original monitor power supply states 10.83A max and the PC PSU +12v is at 15A. will it just draw what it needs or are there other considerations?
I will join up all the ground ( black) wires because the earth braid is quite substantial on the original supply.
I wish I knew more about this !
 
Thanks for the vote of confidence there Dave, here is what I did before I saw your last post:

Attached an old HDD to one of the molex and turned on the old PC PSU( The PSU needs some electrical resistance for it to fire up) PSU ran fine.
Remember I had already joined the green power on cable from pin 16 to an earth cable ( black). Which is in effect the on/off button on a PC switched "on"
Then took a yellow 12V plus and connected it to the central cable of the original PSU from the monitor, then joined three earths from the old PC PSU and attached these to the ground/return braid of the original PSu to monitor cable.
connected up, turned on the PC and got my 30" screen back,

Thanks for the input to all concerned, appreciated.
 
Agreed Dave, 2 yellow and 3 black I think in the final version.
I intend to declutter by taking out all other wires apart from those needed..Probably use cable shroud on whats left
So far the psu runs very cool. Pleased with it!
 
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