iMac DV logic board upgrade

Posted by: gonpostal

iMac DV logic board upgrade - 09/30/04 03:17 AM

I have an iMac 400DV. I have obtained a 600Mhz logic board (with IBM 750) that I want to install to replace my 400 logic board. Everything plugs in like it is supposed to, but the heat sink for the processor is in a different place. Anybody relocated the heat sink yet and is it do-able? How difficult is it to remove the chassis so i can drill new holes? Help and suggestions are welcome...

Posted by: krusher117

Re:iMac DV logic board upgrade - 09/30/04 03:35 AM

I assume you are saying that the processor is located in a different spot on the logic board (so the heatsink is as well) there enough room to buy an aftermarket heat sink and cut it to fit? These are readily available at computer shops and pretty cheap. I'd also look into installing a fan while you have it open. The iMac DV was designed to cool itself through the natural movement of hot air upwards (convection maybe?). However, on my brother's 500 mhz DV iMac I noticed it gets fairly hot. A quiet slow moving fan would probably do wonders.

Combine your new logic board with a fan, larger heat sink, and overclock it here.

You would have a badass iMac laugh

PS. Can you take pics of the logic boards so we can see the difference you are talking about
Posted by: whitlock

Re:iMac DV logic board upgrade - 09/30/04 03:38 AM

Whitlock's guide to messing with your iMac:

Updated: With the heatsink, you will most likely have to remove it manually. That is why you only use the board that the Mac came with.

You just have to remove the four screws on the bottom, and the 6 in the shielding. After that, you then remove the 11(?) screws out of the Logic Board and Down Converter. After that point, you have to remove the screws out of the plastic around the case. Memory tells me it's like 6 screws. After that then you can get to the CRT, Analog, and Power boards.


Remove those one by one, with the CRT last. Then you can get to the back of the board. When you get to that point, you will have removed just about every single component out of the iMac.

My question is: Is it worth it? You have to take out all of that equipment or you will have loose metal shavings that may come back and kill your system later on. SO you will have to take it down that far.

Post edited by: whitlock, at: 2004/09/30 03:43
Posted by: gonpostal

processor location - 09/30/04 03:44 AM

well, the 600 Mhz processor is located about an inch and a half over and down from the 400Mhz processor I originally had. So, it appears I will have to move the heat sink. Where would I put an aftermarket heat sink and fan? the original heat sink is sandwiched between the chassis and the back side of the main board (only about 1/4 inch). I will try to take some pics as soon as I get my replacement board, as the first one burned up :|

Posted by: whitlock

Re:processor location - 09/30/04 03:56 AM

You are going to remove that heatsink. Pretty much because of it's location, it's almost flush with the board. Getting it down half an inch would keep it from making any contact, but if possible try to remove the whole metal block and put a new block where the new processor is. There is really no way around due to it's location. Also the design was made to use the chasis for heat dissipation. You maybe able to slip a small heatsink in there, but it's not going to work very well.
Posted by: krusher117

Re:processor location - 09/30/04 04:03 AM

If I remember right (after 1 dissassembly of an iMac).....that the processor is located on the underside of the logic board? If this is the case, a little creative cutting could make room for a fan to be installed into the bottom. :dry:
Posted by: whitlock

Re:processor location - 09/30/04 04:05 AM

Unfortunatly if the heatsink/fan is too big, the CRT is going to get in the way, because it sits around in that area. So removal of the block and part of the steel frame may allow some room for a fan, but not too much.
Posted by: gonpostal

Re:iMac DV logic board upgrade - 09/30/04 04:34 AM

Hmmm, very interesting...
Maybe what i need is a photo of a later (2001) iMac with the logic board out of it. The amount of clearance from the old processor to the heat sink appears to be the same as the new one, it's just that the processor is in a different location. I was making the assumption that I could drill and mount the heat sink in the proper place so it would work with the new board.

Of course, Whitlock has a very valid point... is this worth my time? I seem to enjoy little projects like this (took apart my old vcr once and spent a week trying to get the gears all timed again...eeek!)

I would be the type to tackle a larger heat sink and overclocking too, but since I've never had the guts to actually do it before now, i'd need guidance....

Whitlock, whats the safest way to discharge the CRT should I tackle this disassembly? Should I use my tongue? :P (okay, not funny)

thanks guys
Posted by: AMoses

Re:iMac DV logic board upgrade - 09/30/04 05:23 AM

I'd like to see how others discharge their CRT's. I'm sure that my method is much more dangerous than it has to be.

Here's what I do:

Neoprene (latex-dipped, high voltage-rated) gloves that I got from Home Depot
2 screwdrivers with long metal shafts and plastic handles.

Always make sure FIRST that there's no connection between the CRT and any sensitive component such as the logic board.

I take the 2 long screwdrivers and carefully touch the metal tip of one screwdriver to the high-voltage wire at the end of the tube and the tip of the other screwdriver to the ground that wraps around the end of the tube.

If the monitor has been plugged in recently, then when I cross the metal shafts, I get a bright blue spark and hear a popping noise.

This discharges the most fatally strong charge in the CRT, but there are other places on the tube that may still carry a small charge... PROBABLY NOT a fatal charge, so it's good to continue to handle the CRT with care. ;-)
Posted by: krusher117

Re:iMac DV logic board upgrade - 09/30/04 07:46 AM

I vote YES! :lol: should defnintely tackle this mod.
Posted by: whitlock

Re:iMac DV logic board upgrade - 09/30/04 08:03 AM

AMoses, that is how you can do it. It is good for someone who doesn't have the right tools. Apple used to make CRT tools, and those were nice. If you can, I'd highly suggest getting a specialized CRT discharge tool, though the act of discharging it (like how AMoses' tool will do) is what matters.

Though the actual tool contains a rubberized handle with a dog clip coming from the handle, which is an extension of the probe. You clip the one end to the metal frame, and then you poke the tip under the rubber cap to make contact.

By the way, if done with proper tools, you NEVER see sparks. In the time that I did pro repair on iMacs, I never saw sparks. That seems a bit dangerous AMoses, and I may suggest investing in one of these tools. It doesn't take much for that high of voltage to jump. Just worried about safety.
Posted by: krusher117

Re:iMac DV logic board upgrade - 10/10/04 08:06 AM

I have a 21 inch apple monitor that im bout to take apart. Does the monitor always need to be discharged? It hasn't been plugged in in about a month.
Posted by: mark

Re:iMac DV logic board upgrade - 10/10/04 09:11 AM

Its a good idea to. Every Apple product with a CRT since the Mac Plus has had auto discharge built in, but circuits can fail. IIRC Apple techs are supposed to discharge the CRT when working inside a monitor, but I know that a lot of hobbyists don't bother. Personally, I think its better to discharge than to get a nasty shock.
Posted by: ubergeek89

Re:iMac DV logic board upgrade - 10/10/04 11:46 AM

I may be doing this on one of my iMacs, so would a car cylinder cancelling probe suffice? If you don't know what it is it looks like a screwdriver with a completly pointed tip and has a lead with an alligator clip on the end which works the same way as a grounding bracelet.

Post edited by: ubergeek89, at: 2004/10/10 11:47
Posted by: whitlock

Re:iMac DV logic board upgrade - 10/10/04 12:14 PM

If the aligator clip is attatched by wire to the end of the 'screwdriver end', then yes. You use the pointed end to lift up the CRT rubber cap to discharge the CRT. The clip is supposed to be on something grounded e.g. the iMac frame. I always suggest having the machine off 10 minutes before opening it anyways because they tend to discharge properly 90% of the time, but the other 10% is why you do it. And for safety measures, you should always discharge a CRT before working with it or the power/analog boards that are attributed to it.
Posted by: ubergeek89

Re:iMac DV logic board upgrade - 10/10/04 12:44 PM

I took apart a monitor once before (when I made my performa plus monitor fishtank), an did not discharge it. I would like to say for anybody elses case, I personally would recommend wearing thick leather gloves when doing so. I don't know if it will do aything, but trying to be safe isn't a bad thing.
Posted by: gonpostal

success! - 10/10/04 01:41 PM

I just thought I'd let everyone know that I was successful. I moved the heat sink where it needed to be and installed the new board. I did not remove the tube or the board above the Chassis, but I still drilled my holes. wink I used adhesive tape to catch the shavings and a can of air to ensure I had no stray metal. It's been running for about 3 days now without being shut down.
Posted by: whitlock

Re:success! - 10/10/04 08:23 PM

Good job! I would like to see a couple screenshots, along with a pic of the case too. Sure, a bit unorthodox, but it worked. Congrats on your faster iMac now! It must feel good.

B) smile :y32b4: :blink: B)
Posted by: oojacoboo

Re:success! - 10/11/04 09:51 AM

gonpostal, everyone would love to see the mod. If you can post a mod guide it will be reviewed for posting. If it is indeed unique we would love to put this on our site so that others will have something to follow if they are interested in something similar. wink