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Old Feb 21, 2009, 10:26 PM
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ancora imparo
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Melbourne, Australia
Joined Jul 2005
8,250 Posts
Hi feathermerchant. They look a good solution and great value as well. The problem for those of us not in the US is that the shipping on any of your local solutions is a killer because of the weight of these little beasts. That's really what prompted me to look for an alternative locally and I figured being HP they are going to be available pretty much worldwide.

I think I prefer the method of soldering the cable inside the two blades for a number of reasons. It's easy to fit a wire to every blade pair and join them at the connector which spreads the current evenly across the PC Board tracks, it's very convenient to add the strain relief with a couple of cable ties through the back plate, and it's really simple as the blades hold the wire while you solder.

There's no magic secret to figuring out how to turn them on.

1) If you don't have any documentation then you have to hope it's your lucky day since it is a Catch 22 situation. Until you get it to run you can't measure voltages and until you can measure voltages you can't logically work out the likely right answer to get it to run!

2) You have to hope that a simple pin combination will do it and they don't rely on any timing or order of pin pullup to do it. If they do you are out of luck. My guess was that these hot pluggable devices would be pretty conservatively designed and as simple and fail safe as possible. I was banking on simple high/low logic to tell them what to do.

3) You take one apart and have a look at the PC board and figure out what the various pins might do. (Not recommended unless you know what you are doing though as these things have a couple of very healthy capacitors in them that may or may not discharge when it is turned off. I wouldn't want to find out which the hard way!)

That's what helped me find that the 3.3V was on the logic plug not the high current blades which was the obvious first assumption. It also eliminated a number of the smaller pins which were joined together as the 3.3V line.

4) A multimeter identifies all the grounds and whether they connect to the case.

5) It's then just a matter of trying all the pin combinations in a logical exhaustive sequence. Only a fool and a Darwin Award candidate would go round shorting out the outputs of a 1300Watt device at randomn so I used a 1k resistor between pins on the assumption the worst I could get was 12mA of current.

One clue was that there was 1 pin shorter than all the others. I figured this last to make/first to break pin would be the one that said it was finally OK to start up and so I started with that grounded and tried all the others. Fortunately it worked - and no, I have no idea why. Maybe someone with genuine PS knowledge of these things can tell us.

Just for the record. If you don't apply some logic and observation then the only alternative is to try all the pins, 2 at a time, then 3 at a time and if that doesn't work 4, 5 .... at a time.

The number of combinations of 2 pins out of 28 is 378, for 3 pins it's 9,828 and if it needed 4 pins connected to start there are 245,700 different combinations you would have to try. And that's assuming that they were all connected to ground or V+ not spread around.

UPDATE: Two years on and we have a lot more info on these supplies. xandrios has posted a lot of detail on how these work in later posts, including the pin out and logic. Starts around post #495

Here's his summary from Post #570 on how to solve an unknown supply

Bringing that up, this is the method I used to find the correct pins to power up this supply. It also works for a majority of PS units out there.

With power off and testing each pin to ground.

1. Exclude any pins that are common to each other(including ground pins). Usually these are the 3v and 5v rail pins. They also show the same resistance.

2. Exclude any open pins(pins with no resistance that don't connect to anything).

3. Exclude any pins with a value below 1k ohms and above 10k ohms. From my experience, I've found that the pson and pskill resistance usually falls between a 1k and 10k range.

With power on.

4. Exclude any pins that show no voltage.(pson and pskill are held partially TTL high or just not grounded. So they show some voltage on them).

This will usually leave between 4-6 pins.

Use a .5k ohm resistor on each of the individual remaining pins and connect each to ground. The power supply will usually power up at this point.

Disconnect one resistor at a time from ground.

If the PS remains on after a you disconnect a resistor from ground, then the remaining pins contain the pson and pskill. So keep it disconnected from ground.

If the power supply turns off, then the disconnected pin is either the pson or pskill. So reconnect it to ground.

Repeat this process until you find the pson and pskill pins.

In some cases the PS will turn on with a fault.

If this happens then disconnect one resistor(pin) at a time from ground to find the one that is causing the fault. Then continue with the process above to find the pskill and pson pins.

Even with the 32 pins on the Poweredge 6800 PS, I was able to narrow it down to just 5 pins before I even tried to power it up. It took just under 20 minutes.

Posts #598 599 here:

Contain useful info on finding the pins which turn a supply on and control the regulation if you have an unknown supply or want to raise the output voltage a little.
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Last edited by jj604; Apr 24, 2011 at 04:44 PM.
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