Results 1 to 8 of 8

Thread: iMac OC Disaster

  1. #1
    Join Date
    Nov 2001
    Location
    Harrisonburg, VA 22802
    Posts
    4

    Default

    Some of my friends and I recently attempted (a.k.a. "butchered") to overclock a working Rev. B iMac (complete with a Game Wizard Voodoo2,160mbs of RAM, stock HD) that a friend of ours let us borrow. He was informed about what we were going to try to do, the risks, etc., and he still let us go through with the operation. During the process, (it took about 9 hours straight, from 6pm to 3am, with liberal rest periods, and late-night runs out to the local pizza place)we succeeded in completely dissassembling the entire case, including cosmetic paneling, and losing resistor R120 on the logic board, and ripping in half resistor R121.

    On a high note, we did succeed in applying a nice coat of Arctic Freeze onto the bottom of the stock heatsink, and created a large enough hole right under the iMac's handle, on top of the outside case, in which we fitted a beastly 120cm fan. Its intended purpose is to suck all the heat coming off from the CRT area above the logic board and blow it out right where the handle had been. As of yet we haven't managed to supply the fan with power, as we THINK that the internal power supply is nestled (or guarded) by the CRT, and none of us really relished the idea of getting a potentially fatal shock at the time.

    So,after we re-assembled the iMac, and when we tried to start it the LED power light on the front of the case came on, but it stayed amber. Normally, under un-modded operations, it would turn amber for a few seconds, and then turn a nice healthy green when the monitor itself comes on. However, this did not occur. What did occur is that the OEM fan inside turned on, and that's about it, aside from the front power LED turning on. By the way, we also connected the stock keyboard and turned the iMac on using the keyboard's own power key, but the same thing happened. (Theory: Wouldn't that indicate that the logic board's USB ports are working, since the keyboard itself has to be connected in order to provide a power signal to the computer?)

    As of now, we're considered buying a costly-yet-working replacement logic-board, unless we get any good responses from this post. What should we do? Any theories on what's wrong with iMac? If the problem itself could be found, and we could be absolutely certain that that was what was causing the problem, then that would be great, as we could try fixing it, if it doesn't require anything drastic. Also, any ideas about connecting the second fan to the iMac's internal power supply would be great, too.

    Thanks in advance!
    Artemis




    ------------------
    "There might be less software on the Mac side of the aisle, but a lot of what's produced for Windows isn't all that good. Crap does not survive in the Mac market."

    [This message has been edited by Artemis (edited 12 November 2001).]

    [This message has been edited by Artemis (edited 12 November 2001).]

  2. #2
    Join Date
    Oct 2001
    Location
    Varies widely
    Posts
    100

    Default

    First thing I'd try would be to take it back to its original state and see if it works at the original speed.

    BTW, how did you rip an SMT resistor in half? That's pretty difficult...

    And what speed are you trying to achieve? If it's more than about 333MHz, I don't think you'll have much - if any - luck. The G3s don't overclock more than about 30-40% too well.

    p

  3. #3
    Join Date
    Nov 2001
    Location
    Harrisonburg, VA 22802
    Posts
    4

    Default

    We were aiming for 300mhz, if we were lucky. Now, if we're even more lucky, we can get the thing to work at the normal speed. We never did achieve getting the resistors into a configuration that would result in a faster clock speed. For we know, we could've accidently found the Secret Resistor Configuration of God Himself that is clocked at 600mhz, but first we've gotta successfully get the thing to boot.

    About the resistor: it got ripped in half by the combined might of an errant stab of the soldering iron and a clever wrench with the tweezers. It will be missed.

    Artemis

    ------------------
    "There might be less software on the Mac side of the aisle, but a lot of what's produced for Windows isn't all that good. Crap does not survive in the Mac market."

  4. #4
    Join Date
    Jul 2001
    Location
    Las Vegas, NV, USA
    Posts
    1,559

    Default

    No problem Artimis. I deleted the extra post for you. If you have this problem in the future though, you can delete your or errant post by going into the edit mode (click the pencil/paper icon to the right) and check the delete box before the Submit button.

    I certainly hope that iMac wasn't too important to you and I hope you're able to restore it to it's original pristine condition. It's not enough to change the multiplier on just the processor card, but both the multiplier and bus clock would need to be adjusted appropriately on the main logicboard to match.

    I would not consider hooking up the fan up top for a couple of reasons. The iMac was designed to vent the heat properly away from the computer logicboard. While the top of the computer does get very warm, this is where it's supposed to get warm. The second reason is the voltages present in that area include the approx. 20,000 volts at the CRTs cathode connection (That thick wire coming off the side of the picture tube, otherwise known as the Flyback). This high of voltage can jump inches (yes! Plural!) and could fry the power supply if it jumps to your fan or fan's wires.

  5. #5
    Join Date
    Nov 2001
    Location
    Harrisonburg, VA 22802
    Posts
    4

    Default

    What do CPU fans need to be able to operate? If all they need is power, then I think that it would be feasible to just strap a battery pack on the top of the iMac's case and run it like that. Otherwise, if the fan needs a motherboard connection to run, then we'll probably just have to forget the beastly fan idea altogether.

    We told our friend the horrible news and he took it admirably well. As it turns out, he was looking into buying a new Mac in the near future (a dual G4 500, to be exact), and he said that the iMac thing was no big deal.

    About the future of the iMac, we really don't see that it'd be financially smart to cough up a couple hundred for a completely new logic board, just to revive a machine that's aging anyway. It looks like we'll probably sell 'im for parts or something. Of course, if we could find an older iMac and just scalp that one for its logic board, we'd be set, but of course we don't have one yet...

    Thanks so much for your help!
    Artemis






    ------------------
    "There might be less software on the Mac side of the aisle, but a lot of what's produced for Windows isn't all that good. Crap does not survive in the Mac market."

  6. #6
    Join Date
    Oct 2001
    Location
    Varies widely
    Posts
    100

    Default

    Find yourself some old motherboards or whatnot (or e-mail me) and grab an appropriate replacement resistor off one of those. I'm firmly of the belief that it's pretty hard to screw up a mobo if all you did was break a resistor and move another one. My Wallstreet/266 works great at 266, but when I tried to go 333 it wasn't happening - just sat there with much the same symptoms as your iMac. It probably isn't dead, just temporarily comatose.

    If you used the directions on Takashi Imai's site (the only iMac overclocking directions I know of, and ones that correspond to your fooling with R120, etc.), then there isn't any need to mess with bus speed multiplier or anything like that - moving the resistors on the CPU card, if Takky's pictures are accurate - is all you need to do.

    p

  7. #7
    Join Date
    Nov 2001
    Location
    Harrisonburg, VA 22802
    Posts
    4

    Default

    Sounds like a plan. I'd really hate losing a machine that I paid $900 for, so I think I'll try to grab another mobo off of eBay or something. Would it be better using the exact same resistor (same number, from the same location on the motherboard) from another iMac board, regardless of revision, or would just any old Mac mobo work?

    And another thing: what kind of soldering equipment would you reccomend for this kind of soldering? We were using a 20 watt iron (not a gun) at the time, and we were having to hold the tip of the iron onto the resistor's solder for sometimes up to a minute until we noticed the solder melting or even reacting. Any tips/hints/prayers would be appreciated.

    Thanks for your help!

  8. #8
    Join Date
    Jul 2001
    Location
    Las Vegas, NV, USA
    Posts
    1,559

    Default

    A temperature regulated iron with a fine tip is best for SMI components. Unfortunately, I know of no low cost alternatives. I use a Weller and swear by it. Rarely at it.

    Were you able to read the numbers off of the components you removed? Depending on what they were used for dictates whether you can deviate from the original value. If the original component was marked with only a zero, you can substitute a jumper wire. Just be careful if a trace is running between the contacts.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •