Saturday, March 5, 2011

The Two 17" iMac Necks

*NOTE: The Inverter Charts have been updated.  As I noted earlier, a reader noted flickering of the backlights with 12V connected to the RED line and it stabilized when connected to 5V.  I initially thought there was some inverter variation but after another confirmation from a reader I checked my old notes and had clearly written "Red - 5V".  I made a mistake when putting together the Inverter diagram for the blog.  Thank you to my readers and my apologies for any inconvenience.  Please note the charts have been corrected to reflect that RED is connected directly to 5V for both 17" iMac necks.

So I have fairly intact versions of both of the 17" necks and they are VERY EASY to tell apart - even if you don't know which 17" iMac the neck originally came from.  They are also VERY DIFFERENT - so know which one you are using before proceeding.  These are the only two part numbers for 17" necks I have been able to find.  Other variations or small differences may exist, I can not be certain.  Remember, you always have the option of opening up the monitor and looking at the JAE connector.  Because they all use the same LCD, the pin number/position will always be the same.  I will focus on the differences.
My previous post/17" pinout detailed what I will call:

NECK A: This is part #661-2825 and is the for the 1ghz and 1.25ghz 17" iMac G4.

 Here is a picture of the JAE connector.  Notice that the pins are glued onto a black board which is then encased in a silver connector with prominent push clasps on the sides.
 Here is the inverter - LCD side.  Notice the colors from left to right (Blue, Black, Red, Green, Purple, ORANGE)
 Bottom of the inverter again you can see the presence of an ORANGE wire
 The bottom of the video cable that plugs into the motherboard had this number on it (620-2305).  I don't know if this is universal across all of these necks, but I wanted to point it out).

DVI pinout A - 1 or 1.25ghz iMac neck
Inverter Pinout A: 1 or 1.25ghz Neck

So here again is the DVI and Inverter pinouts for Neck A recognizable by:
1) Part #661-2825
2) Comes from a 1 or 1.25ghz 17" iMac G4
3) Has a black/silver JAE 30 pin connector to LCD
4) Has an Orange Wire in the inverter cable
5)??Has the number 620-2305 on the motherboard side of the video cable

NECK B: This is part #661-2716 and is the for the 800mhz 17" iMac G4.

I have peeled back the aluminum foil, but you can see that the JAE connector that connects to the LCD is one where the pins snap into a beige connector and there are no clasps on the side.

Here is the inverter (LCD side).  Notice the colors from left to right (Blue, Black, Red, Green, Purple, OFF-WHITE) 

 The bottom of the inverter (removed from connector) again shows the OFF-WHITE colored wire [NOT ORANGE].  There is also a number on the motherboard side of the video cable.  Again, I'm not sure how specific this is.  (620-2122).

So here is the new TMDS to DVI and Inverter pinouts for Neck B recognizable by:
1) Part #661-2716
2) Comes from a 800mhz 17" iMac G4
3) Has a beige JAE 30 pin connector to LCD
4) Has an Off-White Wire in the inverter cable
5)??Has the number 620-2122 on the motherboard side of the video cable

DVI pinout B - 800mhz iMac neck

Inverter pinout B: 800mhz neck
*** I have come across a neck that has the LCD cable of a 800mhz iMac, however, its inverter cable has an orange wire.  As I obtained this second hand, this could have been the result of a repair and may not be standard.  As both are left floating, it doesn't matter for the inverter, however, I can now have doubts if this can be used to differentiate the two necks.  Luckily, there are other differences.

There are so many differences, there is a Brown cable in one, an Orange in the other.  The order of the rest of the wires is completely different.  Even the Clock/Data cables are reversed White/Black.  While I myself have set up Neck A, a reader of my blog has gotten it working with neck B.  Obviously the color of the wires really doesn't matter its what pin they connect to thats important.  As there may be a slight difference in what I call "blue vs. purple" etc.  Here is a close up of the 2 JAE connectors and the order of their wires (pin 1 position is on the left to pin 30 on the right).

NECK A: 1 or 1.25ghz 17" iMac
I'm excited to see some of the projects people come up with - I also like confirmation that things are written clearly and are correct.  So comments are appreciated - thanks.  Good luck and feel free to ask any questions.


  1. Hello JBerg, I stumbled on your blog searching for info on my 17" G4 iMac. I don't know if you will respond but I have a couple of questions.

    Sadly the old G4 is getting a little bit sluggish these days. I've overclocked it to 1.33 but even so the kids complain that it's too slow :( The overclocker refused to tell me the pin combinations for higher speeds saying the processor would fry! So I've been looking at the first gen "plastic" iMacs. They seem to be pretty cheap so long as they have a busted screen!!

    So my first question is would the 17" G4 1440x900 screen simply slot in to the 17" Intel 1440x900? If it would then how on earth do you get the display out of the G4's enclosure?! Preferably not using an angle grinder!

    I don't want to shoe horn a Mini board (Mac or ITX) into it, besides Intel Mac Minis are still pretty expensive, even Core Solos. Are there any other speed mods that can be made to the G4?

  2. Hmmm, seem to have managed to answer my own question. The G4 is TMDS while the Intel is LVDS. So the answer is no, not without a conversion board.

  3. It appears that the G4 iMac screen simply has a TMDS to LVDS converter just prior to the display. So back to plan A and any advice on how to crack open the G4 display panel, it appears to be epoxy bonded!

  4. OS1: Yes there is a special Texas Instruments chip that turns a TMDS signal to LVDS within the monitor itself. I have heard other modders say that if you connect LVDS the chip just allows the signal through, so the monitor can accept either LVDS or TMDS. I myself can not confirm this however.

    Unless your iMac has been modified, to open the display look at the bottom of the monitor display. There are 3 small screws. These are torx-6 screws. You will need a torx-6 screwdriver, do not mess around with anything else. (Torx-6 screwdrivers are readily available at any basic hardware store). These screws strip very easily. Once the screws are out. Pull the front of the monitor out from the bottom half. The front of the display will pop out.

    Note that the lcd screen itself is actually attached to the front of the monitor.

  5. Excellent, many thanks JBerg. I want to use the sacrifice of the G4 as a last resort but it's good to know I can.

    I also tracked down the clock jumper settings for the G4 iMac so I may send it out in a blaze of glory, in part just to see what can be squeezed out of it. It was a 1.25 as was my old G4 Mini. The Mini runs quite happily at 1.5 so I suspect the iMac will too. The max 1.66 may be pushing it though. Have you ever overclocked the G4 iMac?

  6. JBerg, thanks very much for this confirmation, very useful. I can confirm that my 17" reflects everything you mention in the (620-2305) neck and monitor above. Down to the (620-2305) label around the video cable everything is the same. I will be following your guide and I'll let you know my progress.


  7. OS1 - I never have tried to overclock it, sounds interesting though.

    Tobi - Thank you for letting me know - I appreciate it. Please keep me updated on your progress.

  8. JBerg - the two sites for indications on how to overclock are and ; macflowerpot appears to be intermittent but I have a printout :-) If you try let me know how you get on. I'm not going to try it until I have at minimum a replacement mobo!!

  9. hmmm, it removed the URLs!!

    Try 2

  10. blimey, how does it do that!

    Try 3

    ethernetworks dt de forwd slsh imac_g4_usb2_overclocking dt h t m l

    macflowerpot dt c o m forwd slsh clk dt h t m l

  11. In the Inverter pinout, what is a "Floating" wire, and what do I hook it to? Or is it just there for looks?

  12. I left it not connected to anything. It's the brightness control. 0V is full brightness by default while I believe 3.3V is fully dimmed. I didn't want to put not connected because it's not a useless wire, you could connect it to a switch or regulator to give yourself a hardware brightness adjust if you wish.

  13. Awesome. Also, On your pinouts, you state 5V (3.3V) as the power requirements. Will either work? I'm using a power supply that's producing exactly 5V. Do I need to find one at 3.3V?

  14. If you check it with a multimeter it does read 3.3V, but I - like you - only had 5V - it worked just fine. Now, could there be long term consequences to using the higher voltage, that I don't know, but it did not alter image quality at all.

  15. Hey I just got mine working, but it looks like for mine, 0V is fully dim. I need to find a 3.3V AC Adapter to verify, but mine was pretty low.

  16. New theory, I gave it the 3.3V (3.75V actual) and the brightness increased by an incredibly tiny amount (I had to hook it and unhook it a few times to know for sure the brightness change wasnt in my head). Any Ideas?

    My best theory is that 3V is fully dim, but you need a small voltage in order for it to be fully bright. Unfortunately, I don't a smaller voltage AC adapter (1V or something similar) to see if that's right. Is this completely bogus?

  17. I have never had a similar brightness issue to be honest. 0V should be maximum. Even when I hook just the inverter up, the screen is quite bright without the orange connected. Out of the 4 or 5 people who have replicated this the only issue one reported was using 5V instead of 12V for the red wire. Try this switch if you haven't yet.

    I recommend hooking up ONLY the inverter to have just the backlights on. Look closely and see if one side is brighter - could one of the CCFLs be out? Check your resistors make sure they are 1Kohm and rated at least 1/2 amp. Switch them out. Third it could be either your inverter, CCFLs, or power source. If you still have the other 17" LCD (even if the LCD broke - the backlights should still work). Hook the inverter to that LCD - if it's fully bright - you can assume the CCFLs are failing, if it looks similar you may want to consider a replacement inverter. Also what are you using for a power source? You may just want to check the voltage on each line with a multimeter.

    If you look at the pic in my "17" inverter confirmed post" and my "17" pinout confirmed post" the screen is quite bright. I can assure you that there was no voltage connected to the orange wire for any of these. Let me know if this helps at all.

  18. Hi JBerg,

    I am finally giving the screen wiring a go.
    I was wondering how you were able to get so many lines connected through the single 5v line of the molex adapter.
    I followed your suggestion to another commenter and wired the inverter cable first just to see if I could get the screen to light and nothing happened. It is very likely that my wiring is incorrect even though I think I followed your instructions correctly using the resistors and so on. If I am not able to get the inverter wiring correct, I am not too optimistic about the dvi/tmds wiring either. Any help or advice you can give me about the wiring, how to properly isolate the wires to avoid crossing signals or anything like that would be greatly appreciated. Thanks.


  19. Do you have a pinout for the 15" 700mHz?...I want to practice on something cheap before I destroy a 17" :D

  20. Yeah, I'd actually love to know how you create those pinouts.

  21. Tobi - I actually purchased a molex splitter cable then cut off the ends (the two heads after the split) and stripped them - this just makes it physically easier. As long as you use separate resistors (do not go through 1 resistor to multiple lines). Then you should be fine.

    Start with the basic stuff - is whatever power supply you're using actually on and working? Meaning if you have it hooked up to an atx power supply - have you jumped it? Are your resistors 1kohm rated for at least 1/2 watt? Do you hear any noise from the inverter?

  22. Bibby - the original 15" pinout came from Japanese modder. But the easiest to follow chart was developed by a very talented modder. Go to this forum :
    About half way down you'll see a post by pgee70 with a picture of the 15" monitor working. Follow his links. I myself have never done the 15" mod - but it appears as though it's been replicated.

  23. Dave - the absolute easiest way as I did is to try to find the spec sheet for the monitor. That's where the pinout for the 17" came from. See this post:

    The pinout was exactly as it should be. Again this is a TMDS monitor - LVDS is much more of a pain. Just match up the pins to their DVI counterparts and there is the pinout. Some caution - be careful with LCD panel numbers. You will notice often suffixes such as (A1)(K2) etc. Even though the panels match - different suffixes mean different pin outs. however, it's not hard to figure out even without the pinouts.

    For 17 - 22" monitors you'll usually have 4 channels recognizable by the presence of a positive, negative and shield (usually they are sequential but even if you try out every combo - that's only 24 possibilities. In every JAE connector I've seen these are at the left (but not in the first which is often a ground if used).

    The middle of the JAE connector has the hot plug and ground (often next to each other) and the clock and data (often next to each other). So if you have a mutimeter and a working source just find the one with juice. (usually 3.3v is the hot plug). Also hot plug tends to have a bright color and grounds dark. Then the cables far right (usually 3 in this size range) are the vcc and the rest are grounds. As you go up in size, you tend to get more vcc plugs and grounds. But a multimeter will again answer all these questions.

    17" tends to be 3.3 or 5V while 20" is 5" or 12". I learned the resistor to hot plug trick from pgee70 which allows it to turn on. LVDS is another story altogether and inverters are guess and check. You can usually tell ground wires by looking at them. And 2ccfl inverters usually need 12V max while 6ccfl inverters need 24V. Hope this helps.

  24. so i have a tiny intel board that i'm going to try to squeeze into the base. it outputs an lvds signal. before hooking it up, and risking hurting something (more than modding the heck out of my old mac) are you guys sure it will work? and that the TI chip will just let the signal go through? thanks

  25. I have never done it and 100% can not confirm it will work. When I di an LVDS mod I changed the screen. Also, the wires in the neck are designed for a TMDS signal (bundles of 3 including a ground). Also, just because something is LVDS doesn't mean the pin out will match what you have on your board. Even with identical pin functions the order can vary widely. I found the technical specifications for the TI Panel Bus on a modders website in PDF. This may help.

  26. Dexter - I have never done it and can not give you any guarantees all I have seen is posts on blogs. I would stick with TMDS - it's stable over long distances (why apple chose it), the wires are already designed for it and I can guarantee that it woks. If you have a DVI plug then your board technically has a TMDS out as well. The only thing missing is the power, but you need to power th inverter anyway.

    Just curious if you considered a nano or ecx board?

  27. Yeah don't do it. I plugged an lvds monitor into a tmds cord and it fried the controller board straight up. Like jberg suggested, stick with the tmds/dvi

  28. JBerg - i have looked, but can't find any on the supply sites i use. if you could, would you please list some websites where i can find these types of boards? also, can they support Intel chips, like the core i series processors? or the core 2 duo? this will make or break the build, as i am going to hacintosh it and haven't found an acceptable way to get mac to run on an amd or other type of processor.

  29. also, how would i go about powering the inverter? with an atx power supply? or do i need to make something for that?

  30. hey. if you have a account, i have a site there that i built to handle this discussion. i feel like it will help me more, because i will have a central site that i can go to and see stuff about mods, instead of on the multiple blogs i am commenting on.

  31. Try

    Yes you need to power both the LCD and the inverter. Although I'm not done with the tutorial - look at the parts list for power source ideas in this post:

  32. whats mean red to red can i must connect 1 red cable to other red cable? can i must use this multimeter with resistors its complicated ;/

    1. Not sure what you are asking but try clicking the tabs at the top of my blog specifically to see my 17" STEP BY STEP or VIDEO tutorial, this visualization may help you

  33. can i use this dvi because hard to find exactly the same molex which you used ?