Introduction: Replacing the Power Supply for a Cisco Pix 506e

About: At the age of 6 I disassembled my mother's blender ... and somehow I managed to convince my folks not to kill me :-) From that moment on my family called me "Disassembling Engineer" :-) I love taking apa…

Hello everyone, this is my first instructable, but I use this site all the time and I'm glad I'm finally able to give something back.

A couple of years ago I got an old Cisco PIX506e to use as firewall for my home network.
This is a really nice equipment and even if they are a bit complicated to configure, they are very reliable.

Well, about a month ago my PIX stopped working ... a little troubleshooting indicated that the power supply was dead.

I looked around but I was unable to find any supplier in Argentina (where I currently live), and while i could get one off EBay for about U$D 20 the shipment to South America would increase the cost considerably (not to mention the Custom's Fees once in here)

So, I started looking for alternatives.

I check with a local Radio/TV repair store and they could look into fixing it, but I would have to pay a "diagnostic fee" of $40 (about U$D 10) in order for them to tell me IF they could repair it (and for how much).

I might still take it to repair, but I wanted a cheaper solution.

This instructable will show you how I adapted an old "AT type" Power Supply from a discarded computer to power a Cisco Pix 506e.

I'm describing what I done (except noted) and what it worked for me, to the best of my abilities and as much as I can remember.
If you want to follow this instructions do it at your own risk.
Don't hold me responsible if you hurt yourself, ruin your equipment, burn your house, or cause a rift in the space-time continuum .

Step 1: The Power Supply

I opened the PSU hopping to find a component obviously bad (so I could just replace it and move on), but there was nothing that I could detect as bad.

The exterior of the PSU was a lot more helpful, it clearly stated what the 8 pins were for:
      Ground      Ground      Ground      +5v
      ON/OFF      -12v           +12v         +5v

 5v     4   A
12v    1   A
-12v   0.1A

When I found this, I realized that this voltages and Amperages are within the range supplied by an AT PSU, and I happened to have one laying around.

My friend Google pointed my to this site  where they confirmed my suspicion.

So it was now time to do it.

Step 2: Parts and Tools Needed

You will need:
* An old Computer AT Power Supply (please test it before starting) with P8 and P9 connectors (the one on XT computers)
* electrical tape (or heat shrink tube)
* (Optional) the power switch from the front of PC cabinet.

* Screw drivers
* wire cutter
* wire stripper
* Exacto Knife
* MultiTester (or Voltmeter and Ammeter)

Step 3: Preparing the PIX

Why Doing this?
      As I mentioned before, I might in the future take the Power brick to a professional show and get it fix, so I did not want to cut the power cord or modify the brick in anyway.
     If you are not worry about it, you can skip the next couple of steps and take a look at the one about alternative wiring.

Prepare the Pix:

      1. Unplug all cables
      2. Remove the bezel (be gentle, you do not want to break the retaining tabs ... like I did)
      3. Remove the 4 screws in the sides
      4. Place the pix in a flat surface and slice the top backwards until it unlocks and you can pull it up
      5. Check the wiring 
          You Should see a cable running from the external power plug on the back, into the motherboard on the front of the unit. (See the first picture)
      6. Unplug that Wire.
          it should look like the one on the 2nd. picture (Molex connector??)

Step 4: Modifying the Molex Connector

Why Doing this?
          As I mentioned before, I might in the future take the Power brick to a professional show and get it fix, so I did not want to cut the power cord or modify the brick in anyway.
          If you are not worry about it, you can skip this step and take a look at the one about alternative wiring.

P8/P9 connector

          The old "AT" Style Power supply have 2 Molex connectors (usually white) labeled P8 and P9 (pictures 1 and 2).
          This connectors have a similar form factor to the internal power connector in the PIX506e, but they are keyed differently, so we will modify P8.

Remove all wires
          The first step would be to remove all wires connected to it, as they are not in the correct order for our needs
          The metallic connectors inside the plug have a small tab to secure it in place (pictures 3 and 4), we need to (gently) close that tab in order to pull the wire out.
           I tried different approaches to do this, and I found that the easier way is to punch the plastic with a small screw driver or a strong needle or wire, in order to push the pin. (look at pictures 5 and 6)
          Once the pin is receded you can just pull the wire out, repeat for all reminding wires.

Rekey the connector.
          Comparing P8 and P9 (picture 2) against the one inside the PIX (picture 7) I noticed that P8 is the one that most closely matches the original one, but still needed to be modified.
          With a knife or cutter remove all tabs in P8 except for the larger one (see picture 8)
          Is a few steps ahead, but picture 9 shows the modified P8 and the original from the PIX 
          Test the connector
          Test your new connector on the PIX Motherboard, it should fit perfectly (picture 10)

Step 5: Preparing the Power Supply

According to all the wiring schematics i could find (for example in wikipedia) the colors are:
          +5      Red
        +12      Yellow
         -12      Blue
  Ground      Black

      1. You should have at least one of each in the P8 and P9 connectors, cut them out leaving at least 10 cm (4"), except for the blue wire (-12 v)

      2. Remove all other connectors and wire the cables together by color, so all wires of the same color should be connected together.
      3. Besides the Blue, there might be a few other wires that are alone (likely orange and white), leave them alone.
      4. Now would be a good moment to test that everything is still OK.
      5. Power up your PSU and check the voltage and Amperage on the different wires.
          Black - Red        Should show    +5v and at least 4A
          Black - Yellow    Should show  +12v and at least 1A
          Black - Blue       Should Show   -12v and at least .5A

If you power supply does not turn on, it is likely because the interrupter is off :-)
         There should be an extra set of wires coming out of your PSU, likely 4 wires (Black, Brown, Blue and White) wrapped in a black plastic shield.
         This wires are meant to be connected to the on/off switch on the front of the computer case.
         If you can salvage the switch and use it directly.
         If you cannot, connect the following wires: Black with White and Blue with Brown. This way the PSU will be in "Always on" mode.

         I like electronics and electricity, but I know my (low) level of knowledge, so I try not to go outside my "electronic comfort zone".
         For that reason, this process was done completely outside the AT PSU.
         If I were confident enough I guess I would have done all this wiring inside the PSU, to obtain a nicer looking result. If you feel like trying that, check the many instructables describing how to do it.

Step 6: Using an ATX PSU

If you wish to use an ATX PSU instead of the AT style, you should keep in mind a few things.

      1) ATX PSU have a "logical" power control, which allows the OS to turn OFF the PC. This replaces the old style "4-wires" Power switch that the AT PSU had.
          In order to turn the PSU on you will have to follow the instructions on FixedHDD's Instructuable "How to power up an ATX Power Supply without a PC!"

      2) Some ATX PSU will turn OFF if they do not detect a load on the 5v channel.
           While the PIX will provide enough load, this will only work if the PIX is actually ON. If you are attempting the "Alternative Wiring" part of this instructable, you might want to place a small fixed load in the 5v channel. Look around as there are a couple of instructables with details on this.

      3) ATX models do not have P8/P9 connectors, meaning that you will have 3 options:
              a) get a P8/P9 Connector from an AT style PSU,
              b) Use the original internal connector from the PIX, or
              c) Use the "Alternative Wiring option"

Step 7: Rewire the P8 Conector

Why Doing this?
          As I mentioned before, I might in the future take the Power brick to a professional show and get it fix, so I did not want to cut the power cord or modify the brick in anyway.
          If you are not worry about it, you can skip the next couple of steps and take a look at the one about alternative wiring.

      1. grab 2 of the Black wires you removed from the p8/p9 plugs and connect them to the bundle of Black wires (Ground).

      2. grab 2 of the red wires you removed from the p8/p9 plugs and connect it to the bundle of red wires (+5 v).

      3. grab one of the Yellow wires you removed from the p8/p9 plugs and connect it to the bundle of Yellow wires (+12 v)

      4. use your electrical tape or shrink tube to isolate all electrical connections and the end of the lonely wires.

By this moment, you should have 6 wires coming out of you bundles, 2 black, 2 red, 1 yellow, 1 blue. Each wire should have a metallic connector on the end.

      5. check each wire and make sure that the locking tab on the metallic connector is open. If it isn't the open it gently.

      6. Grab the P8 connector with the locking tab facing up and put the wires in the following order
           Blue, Black, Red, Red, Black, Yellow

      7. Make sure to push the wire all the way in, and then gently try to pull it out.

If the wire come out means that the security tab in the metallic connector is not locking (make sure is opened) or that you have not pushed the wire far enough.

      8. Compare the P8 connector to the one originally in the unit (see picture 3) and make sure that the wires match (In my unit Cisco was kind enough to respect the standard color coding except for -12v)

Step 8: Plug It in and Wrap It Up

Plug the P8 connector to the motherboard

Turn on the PSU

Your Cisco Pix Should now be alive.


Once again, I did not want to modify the PIX more than absolutely necessary, and I needed to have the unit up and running ASAP. So I place the cover but leaving a small gap on the front so I could run the wires thru there.

NOT pretty at all, but it works (and no one but me will see it anyway)

Step 9: Alternative Wiring

If you have the original Power supply and do not care about keeping it "stock" than you can power your Cisco PIX in a much nicer way, and without even opening it.

This will way the PIX will work completely "standard", even the power switch will work *

I'm Listing this step to make this post more complete, but I have never tried this part, I'm just suggesting what can be done based on my previous experience.

      1. Unplug the Power Brick. (you should only have one wire, which is the one that plugs into the PIX)

      2. Open the old power brick (there are just a couple of screws hidden under the Rubber pads)

      3. Cut the wires coming from the outside, as close to the circuit as possible.

      4. Use a tester to identify which wire are ground, +5v, +12v, -12v, and power control (they might be identified in the circuit, but you never know)

      5. Join each wire with the corresponding bunch from the AT power supply (the +5v will join the red bunch, the +12v will join the yellow bunch, the -12v will join the lonely blue wire, and the ground will join the black bunch)

      6. use electrical tape or shrink tube to isolate all connections

      7. turn on the AT PSU

      8. Grab your multi-meter and check that all pins read correctly:

If everything is OK, then :
      9. turn off your AT PSU

    10. Turn off the Cisco

    11. plug the power cord into the Cisco

    12. Turn on the AT PSU

    13. Turn on the Cisco.

It should be working fine.

Additionally, this could be done even nicer by doing all the connections directly inside the PSU, but this could be danger if you do not know what you are doing, and definitively outside my "electrical comfort zone".

* The Switch will turn ON/OFF the PIX as long as the AT PSU is ON.
   It's should be possible to use the ON/OFF pin in the Cisco power plug to turn ON/OFF an ATX PSU (But that is WAY over my level of expertise)

Step 10: Final Thoughts

It isn't pretty but it works perfectly ans it was absolutelly free (except for the electrical tape) :-)

I hope you find this instructable useful, as I mentioned in the beginning, it is my first but I would love your comments.

OH!!! if you build your own, please let me know and post a picture of it. !!!