Mac mini 1.25GHz -> 1.5GHz conversion

Discussion in 'Macintosh Computers' started by lbodnar, Feb 1, 2005.

  1. macrumors regular

    Hello guys! It has become quiet here so I decided to speak up...

    I have a good news and a bad news...

    The bad news is that I have found strange glitch with my new Mac mini. Everything works perfectly except Xbench that locks up when it tries to do vecLib FFT part of the CPU test. Reliably crashes at exactly the same place every time... As I said before everything else works fine.

    The good news is that my Mac mini is in fact 1.25GHz Mac mini that runs at 1.5GHz. I can step down to 1.42GHz where Xbench works just perfect as everything else! So I am inclined to think that it is not an instability but some strange glitch.

    Even more the mini starts up at 1.58GHz as well but "About this Mac" shows 750MHz (?) frequency and Xbench locks up at exactly same place on vecLib FFT. Everything else is fine... Very strange... Could this be either overclock protection or some glitch from OF or Mac OS not expecting this frequency?

    What do you think is going on and should I just leave it at 1.5GHz and try to find what happens or get "back" to 1.42GHz?

    Well, at least we can get away with 1.25 -> 1.42 which is quite good anyway...

    I have just took it apart so have not had a chance to discuss it anywhere else...

    Details are available here:


    Attached Files:

  2. macrumors 68000

    After reading the eMac thread, I was wondering how long it'd take for this one to show up. :)

    Got any images and such up yet? Sure it'll be just as valuable a resource, maybe moreso... the mini looks to sell in massive quantity. I'm looking forward to hacking mine - when I have the cash to order it, that is!
  3. macrumors 68020


    So, you're saying you are overclocking the mini? Well, in any case Xbench sucks; I wouldn't put at stock it in. The point at which Xbench is failing will be exercising the Altivec unit, so perhaps Altivec becomes unstable before the main CPU core.
  4. macrumors regular

    Yes, that looks very strange - not like unstable CPU but rather hard stop crashing glitch.

    Can you give me a simple hard test to stress Altivec so that I can try to work it out before I put it all back in one piece? At the moment it is running without case at all...

    Mac mini is great because you can run it without the external shell at all.
    Apart from GPU heatsink. But Radeon is just barely worm...

    Attached Files:

  5. macrumors 68020

    Rod Rod

    Congratulations Leo. You are an inspiration to us all! I don't know if I'd do the processor upgrade, but I'm pretty sure I'd like to install an 8x DL superdrive like the Panasonic UJ-845 if I had the chance.
  6. macrumors 68040


    Very nice, how did you do it? Please let us in on the secret!!
  7. macrumors 68040


    Can I put this in my imac?
  8. macrumors 6502

    please let us know how to do this! i have the 1.25 ghz model
  9. macrumors regular

    I have rolled speed back a bit so I have ended up with 1.25GHz mini converted into 1.42GHz. Which is not bad at all! I want to make sure there is no problem with stability which will take quite some time. Knowing 744x processors I would expect it to be stable.

    Meanwhile I am going to put details on some webpage for others to enjoy. Maybe 1.42 owners will be able to go up a bit more. Basically the speed is controlled in almost the same way as in eMac, by four tiny resistors. I have not located the fifth one. Maybe it does not exist and the CPU pin is simply grounded somewhere. The resistors are on the bottom side of the board.

    I can confirm that power plug does not have any extra secret wires that some were speculating could be used for controlling external devices.

    RJ45 socket has a security feature that prevents you from plugging telephone cord into it.

    Headphone socket also has no extra connections apart from simple stereo output (somebody suspected it can be used for input as well.)

    Again I am blown away by the design. It just a pleasure to hold it in your hands! Mini can easily be operated without the case (making sure the ATI chip is not given too much 3D graphics load without some sort of passive cooling.)

    However I have located some mysterious unpopulated 20 pin connector on the back of the miniboard that connects to the CD and hard drives. It is surrounded by a huge (by mini standards) empty space. I think something was supposed to be there! What do you think it could be? My bet is connector for the iPod mini. It should have been facing upwards and maybe carrying USB/Firewire and power connections? I am attaching the picture for you to look at. Notice the space between the back edge of CD drive and the back of the case.

    Anyway, that's it for now. In the end I have just received the mini today! :eek:

    Attached Files:

  10. macrumors 68020

    Rod Rod

    I'd think so but I can't say with certainty.

    My guess: that's where the hardware digital TV decoder would go (remember all the "this is a PVR" static?) :)
  11. macrumors 6502a



    Did you notice anywhere where one could tap into the 12V power supply?

    Do you have a multimeter to test the voltage going to the fan?
  12. macrumors member

    care to write a 'How-to' page?
  13. macrumors 6502

    Someone did this before the eMac 1.25 overclock instructions are up? Wow. I'm not sure if this is fast or the eMac 1.25 overlocking has come far too slowly :)
  14. macrumors 603

    Dont Hurt Me

    Ibodnar is at it again ;) I have also been waiting for this. I wish ibodnar would have put a photo in here showing the resistors. I have a feeling that both models use the same cpu and in the factory they simply decide on speed depending on demand. I hope this isnt the case cause i was thinking about bumping up my 1.42 a little after it comes. It would be neat if these are the same cpu's in powerbooks. A 1.6 G4 would be sweet to have. Cool ibodnar.
  15. macrumors regular

  16. macrumors 6502

    Excellent work, Kudos to you! I will be overclocking my mini shortly. Any suggestions on a soldering iron to use on such tiny components? As well as any suggestions on what to use for thermal grease on reassembly? Or just stick with the stock thermal pad on the bottom?


  17. macrumors 6502a



    Hope you don't mind...I submitted this to

  18. macrumors 603

    Dont Hurt Me

    Good Job ibodnar. Thanks for the photo.
    Also word of warning if your not familiar with electronics and static precautions you may not want to attempt anything like this because you could end up with nothing but a paperweight. Just thought id mention that for folks with little electronics background. Very good ibodnar very good.

    That system profile you were worried about i wouldnt be, i have clocked up a couple machines and its common. Only problem is there are a few programs and games that looks at the system profile before loading and they may not work after checking it because of the false reading.
  19. macrumors 6502a

    so as expected the mac mini is just one machine, the modechange consists of soldered jumpers in the end, so save the cost of the 1,42 and buy some extra's for that money ;)
  20. macrumors regular

    Thanks, Peyote, no probs, that is where it belongs and I think Mike usually adds it to some FAQ afterwards. He did not believed last time with eMac overclock until I ripped the heatsink off and sent him 800MHz CPU marking pictures. Not going to do it this time, however maybe just to put a better heat transfer compound on? Does anybody know what type of heatpads are between CPU and the heatsink? They are usually on the cheap/convenient side.
  21. macrumors regular


    The thermal paste i used to use on PCs is the one at the top. I found it was marginally better than 'cheapo paste' that came with PC heatsinks.

    And to clean the cpu i used an aerosol of isopropyl alchohol sprayed onto a cotton bud.

    Hope this helps a little.
  22. macrumors newbie

  23. macrumors regular


    Well, yeah. I found it to improve the temperature by about 4 degreesC. But it hasnt scientifically been tested, and there is a chance it might do **** all good.

    I think the most important part is to clean the cpu properly with isopropane.
  24. macrumors 6502a


    When cleaning off the old thermal pad off the cpu, use a lintless cloth like what you use with your glasses so you dont get any lint between the cpu and heatsink. Lint can burn up under high heat damaging your equipment.

    Had this happen to many an AthlonXP before i realized what i should be using.

    Arctic Silver 3 is the best thermal compound money can buy.. For GPU's use Arctic Alumina... Its a sticky compound to keep heatsinks attached.

    Oh and also, only use 90% rubbing alcohol. 70% stuff can damage equipemnt because of the ammount of other chems in it.
  25. macrumors regular


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