Additional Standard Power Connector
on PS/2 25, 30, 30-286, 55
(Revised: 2000-10-29)


WARNING: This is neither a joke nor is it intended for Beginners or Wanna-Bees.
All Tips given and all the described modifications are 'At Own Risk'
The Maintainer will give no warranty of any kind !

Read the entire article first, before you begin !

The Problem: The above mentioned PS/2-models (MCA and ISA) do not have a standard power-supply plug to connect standard harddisks, disk-drives or streamers to.

The Solution: Follow the instructions below and install one !


You need:
  • a soldering iron (a good one - not one for plumbers !)
  • a multimeter with VDC and Ohms-range
  • a sharp knife or cutter
  • a standard power-connector (4 pins - maybe cut from a wrecked power supply)
  • some insulation tape (hi-quality - not that lousy supermarket stuff)
  • alternatively:
    4 selfcutting wire-adaptors - like used to install additional equipment in cars
    (from autoparts supplier)
  • some self-confidence (like always)

It is a good idea to leave the cables on the power connector as long as possible to make it fit on any device to be installed in a PS/2.

The power connector(s) looks like this from the frontside:
(I still love ASCII-graphics !)


             /------------\
             | o  o  o  o |
             +--++--------+
                ++       
               ^  ^  ^  ^
     12VDC ----+  |  |  +---- 5VDC
    (orange       |  |        (red
     cable)     GND  GND     cable)
             (black cables)     

    
  [Fig. 1a: Standard Power Connector]

12VDC-cable may either be orange or yellow


          ++-------++-------++
          |+-------++-------+|
          ++ ##  ##  ##  ## ++
           | ##  ##  ##  ## |
           +----------------+

             ^   ^    ^   ^
    12VDC ---+   |    |   +--- 5VDC
   (orange       |    |        (red
    cable)      GND  GND      cable)
             (black cables)


[Fig. 1b: 3.5"-Disk-Drive Power Connector]

12VDC-cable may either be orange or yellow
Now unplug your PS/2 from everything (especially from mains power !) and open it. Remove disk-drive(s), harddisk and -cabling (if any). Remove the support-bracket and the vertical bus riser-card.

Model 25s need a different procedure to be taken apart. Please consult your manual.

Pull out the two plugs from the power supply to the systemboard.

Hint: This is a good occasion to use a harder brush and a vacuum-cleaner and free the inside of the systemunit and the power-supply from dust. This will give better air flow-through and enhance the systems life-time.

On the 25 and 30 the connectors looks like this:

                                                       
       wt bk or bl bk bk       bk bk yw rd rd rd       
       |  |  |  |  |  |        |  |  |  |  |  |        
       |  |  |  |  |  |        |  |  |  |  |  |        
      1| 2| 3| 4| 5| 6|       1| 2| 3| 4| 5| 6|        
     +------------------+    +------------------+      
     |        P3        |    |        P4        |      
     |                  |    |                  |      
     |          #       |    | #                |      
     +----------#-------+    +-#----------------+      
                                                       
                                                     
                +--------------+---- Key/Marker        
                                                       
                wt = white    Power Good               
                bk = black    GND                      
                or = orange   +12VDC                   
                bl = blue     -12VDC                   
                yw = yellow   - 5VDC                   
                rd = red      + 5VDC                   
                                                       
   [Fig. 2: PS/2 Mod. 25 and 30 power supply plugs]    

On the Mod. 25SX, 30-286 and 55SX the connectors look like that:

                                                             
    J 14                    J 7                              
+-----------+   +-------------------------+                  
| o o o o o |   | o o o o o o o o o o o o | <- Pin 1         
                                              (marked)       
  + + + G G       + + + - G G G G - + G P                    
        N N               N N N N 1 1 N W                    
  5 5 5 D D       5 5 5 5 D D D D 2 2 D G                    
  V V V           V V V V         V V   D                    
                                                             
                 ------------+-------------                  
                             |                               
                  This part is equivalent                    
                   to the P3 / P4 pinout                     
                 in the figure Fig.2 above                   
                                                             
                                                             
[Fig. 3: PS/2 Mod. 25SX, 30-286 and 55SX power supply plugs] 

What to do:

Methode 1 - the solder solution

  • remove insulation at the 4 cables from the power connector for about 6 to 8 mm
  • use a sharp knife or cutter and cut around into the insulation of orange cable at P3-3
    Cut only the insulation - not the entire cable !
    Distance to the white connector: about 2.5 cm (1 Inch)
    Cut around the insulation again 3 mm away from the first cut
    Cut between in the lenght of the cable (Care for your fingers !)
    and remove the piece of insulation between
  • repeat the same at the black cable at P3-6, the black cable at P4-1 and the red cable at P4-6.
  • wrap the end of the orange (or yellow) +12V-cable from the standard connector around the open cable at P3-3 and solder it.
    Wrap the black cables from the power connector around the open cables at P3-6 and P4-1 and solder them too.
    Now wrap the red +5V-cable from the power connector to the open cable at P4-6 and solder it too.
  • Use insulation tape to prevent short-circuits
  • Check the new +12V / +5V lines for continuity
  • Plug back the power cord into the power supply, switch it on and check the voltages between GND and +12VDC resp. GND and +5VDC with a multimeter

    If everything looks fine:

  • Switch off, remove power cord and re-assemble everything, install new harddrive or whatever you want

Method 2 - the non-soldering solution

  • plug a self-cutting cable adapter over the orange +12VDC-cable at P3-3
    Insert the orange (or yellow) +12V-cable from the power connector into the cable-adapter
    Use a larger plier to press the connecting knife blade of the adapter into the two cables
    Flip over the protection lid on the adapter
  • Repeat the previous step with the black cables of the power connector and cables P3-6 and P4-1
  • Repeat the procedure with the red +5V-cable and cable P4-6
  • Check the new +12V / +5V lines for continuity
  • Plug back the power cord into the power supply, switch it on and check the voltages between GND and +12VDC resp. GND and +5VDC with a multimeter

    If everything looks fine:

  • Switch off, remove power cord and re-assemble everything, install new harddrive or whatever you want


Alternatives on Mod. 55 with the Mitsubishi MF355C Floppy Drive

The lot of Mod. 55 that I know are equipped with the Mitsubishi MF355C Floppy drive unit. It has dual pinrow 34-pin connector. If you look at the underside of the printboard where the 34-pin connector sits you find 2 markings:
Pin #3 marked "5V" and
Pin #6 marked "12V"
An equivalent GND-return is pin #33.
If you solder your DC standard-plug cable here it will do too. The frequently used ALPS drives have the same pinout - but here the DC-pins are not explicitely marked.

But: the power drawn via the very thin FDD connection cable should not be too high. You should use one of the later "low power" harddisks, like the IBM DORS, which does not exceed a power draw over 4 Watts in operation / 6 Watts at startup.

(Thanks to Michael Flinck for pointing out the differences and problems with the Mod. 55, which I left a bit unclear.)



Warnings and recommendations:
  • The maximum power drawn from this power connector is below 1 Ampere for 5VDC and 12VDC
    However: if you removed the original harddisk and installed a modern-type harddisk (even with an additional SCSI-controller) the whole thing will do fine.

  • Remind, that the power-supplies aren't that powerful at all.
    Maximum power on Mod. 30 and 55 power-supplies is:
    • +12V 1.80 Amp
    • + 5V 9.00 Amp
    • - 5V 0.11 Amp
    • -12V 0.30 Amp
    Which is a total of 70.75 Watts


Feel free to report experiences.

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© 1997 by Peter H. Wendt / pw-software production