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Macintosh Centris 610

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The Centris 610 appears to be the slowest of the 040 based Macintosh systems as it uses a 20MHz Motorola 68LC040 processor. The case design is shared with the Macintosh Quadra 610, Macintosh Centris 660av, Macintosh Quadra 660av and Power Macintosh 6100.


Clock Mod

Centris 610 Clock Mod Version 1.1
by Guy Kuo

This information is only for those who are technically adept. The process 
requires soldering leads to surface mount components. This is not a good first
soldering project and should be done only with electrostatic discharge safe
equipment and the usual ESD workmats, etc. You will void your warranty. If you
ruin your motherboard, your friends will laugh at you.
Now that you have been properly warned, the procedure:
1) Apply ESD equipment and open the Mac. The power should be disconnected and
   the machine properly grounded. Disconnect and remove the hard drive to gain
   access to the clock oscillator. The metal shield in front of the hard drive
   pops off. The hard drive then slides forward and out.
2) Look just in front of the CPU. You will see a small 4 pin plastic IC
   which is marked 10 MHz. That is the original clock. You may either desolder
   it and replace with a new clock of a higher speed or install a socket. I
   prefer to place a socket.
3) Assuming you wish to add a socket, obtain a 14 pin IC socket. Remove all
   pins except numbers 1, 3, 5, 7, 8, 10, 12 and 14. If you use a machined
   pin socket simply push the unwanted pins out with a needle nose plier. 

4) Cut the socket leads off the corner pins (#1, 7, 8 & 14) The remaining
   four central leads will later attach to the original oscillator.           

5) Use some hook up wire on the underside of the socket to connect
   pin 5 to pin 7.

6) Connect pin 8 to pin 10.

7) Connect pin 12 to pin 14

8) Mount the socket such that pins of the socket match the oscillator pins
   as below. This means the socket's four pins ride on top of the original
   oscillator's leads. Simple lap joint soldering holds the socket in place.

    Socket      Oscillator
      3             1                                                         
      5             2
     10             3
     12             4                              

9) Install a wire jumper between socket holes 3 and 5. This grounds the output
   enable pin 1 of the existing oscillator disabling it.

10) Install a full size TTL oscillator into your 14 pin socket. Pin 1 of the
   new oscillator goes into pin 1 of the socket.

11) Add a heatsink and (optionally?) a cooling fan to the CPU. I routinely
   add a cooling fan on top of my heatsinks for this type of modification.
   A 40 mm low profile 12 volt fan will do nicely.

12) Turn on the machine and it should "Bong" as usual. If not, IMMEDIATELY 
   turn power off and recheck your connections.

If you do not understand how this procedure works, very seriously reconsider
whether YOU should be doing it.

To run the machine at normal speed, unplug your oscillator and remove the
jumper wire between socket holes 3 & 5.

Remember the numbering of the socket top view is:

      14--12   10---8
     |                |
      >               |
     |     /--\       |
      1   3    5----7

The on board oscillator pins are numbered:

          4    3
         |      |
         >      |
         |      |
          1    2

Clock chip speed is 1/2 the desired speed so order appropriately. Do not
obtain clock oscillators with output enable on pin 1 for this procedure.
If you insist on output enable oscillators, you must add a 1 k resistor
between socket pins 1 and 14 to enable your new oscillator.

Digikey at 1-800-DIGIKEY is a reasonable parts supplier. Here are some part

    ED3314	   14 Pin Machined gold contact socket
    HS154ND	   0.25 inch tall heatsink for 68040 with clips

         Some reasonable clock oscillators to obtain are:

    CTX114    10 MHz
    CTX131    12 MHz
    CTX115    14.3 MHz
    X127      14.7 MHz

Please send E-mail so I can gather and summarise successes and problems
with this modification. Good luck and enjoy your new super fast C610.

Guy Kuo <[email protected]>


See Also