View Full Version : G4 "lamp" articulated neck repair

July 7th, 2012, 03:45 PM
[Seems G4 is creeping into the "vintage" definition - mods move this to off-topic if there is objection.]

I'm building a couple of pretty little G4 flat panel 15" units out of the parts of 5 damaged units, including one 17", rescued from dump.

A couple of the necks are damaged, probably through blunt force trauma being chucked into dumpsters. They look repairable to me, from the outside. I've been trawling the Apple user sites and mod sites, and have studied all the Service Source documents available online, but none of them give any useful info on how to safely open and work on the mechanics of those necks. They contain some fairly strong counter-balance springs.

The subject comes up in a few threads but usually ends with somebody advising not to open the neck but just buy a replacement. That's not my game and I'm not giving up yet.

Anyone had experience or know of information source for this:?: I want to preserve these unique machines in as good a state as possible.


August 13th, 2012, 07:37 AM
OK, since nobody responded, I just fumbled forward on my own with one of these necks. In case anyone else finds the thread, here are some findings:

1. The top and bottom bolts are not axels. They are small-guage tension bolts only, and they clamp the two sides of the neck to larger diameter bushes that take the sheer force and maintain the friction resistance of the top and bottom joints. The bushes are lubricated with open-ended omega-shaped composition washers. Tightening the bolts increases pressure on these washers to adjust friction, or (less effectively) on the metal-to-metal bush contact if the washers are missing. Top bolt and bottom bolt are of different diameters, since the top joint allows for the independent swivel of the display in the vertical axis and the bush is of different diameter to allow for more friction resistance to keep the display where it is manually positioned.

2. The bolts are keyed at both ends with three ~1mm holes in even triangle formation. Apple made a three-pronged spanner tool that is no longer available. The torque on these bolts is quite low, so it it is quite possible to turn them with any pair of points that can go into two of the three holes. I used two 2" nails, crossed, with no problem. A pair of fine-pointed pliers might work. No need to fabricate any special tool.

3. The mechanism of the neck is quite simple. A single cantilever inside the neck keeps the base and the display mountplates at the same relative angle while the neck is moved through its vertical arc. A single spring counterbalances the increased load represented by the weight of the display as the neck moves in the arc between vertical and horizontal.

4. Tension on the main spring is too high to adjust or to install by hand. To seat the bushes correctly and tighten the bolts, it is necessary to stretch the spring to a tension of around 150lbs. It is advisable to connect the spring and cantilever bar at the top joint first, then connect the bottom of the cantilever bar to its pin on the rotating bottom bush. I found I could use manual strength, pulling on the base and rotating it, to work the bolt hole to within about 3mm of correct positioning for the bottom bush.

5. To get the final degree of tension and position the bottom bush correctly to close the housing, you can take advantage of the fact that the neck housing has a rounded end. The gap between the baseplate of the neck and the rounded base of the neck body fits into the 1" depth of a wooden workbench vise - "Workmate" type or similar. Tightening the workmate vise against the curved neck base, with the baseplate beneath the vise board, stretched the counterbalance spring enough to bring the bolt hole into correct position, so that inserting and tightening the bolt would engage the base bushes correctly and restore the neck to correct function.

6. In the neck I worked on, the original bottom bolt had been lost. A 1/16" bolt with various washers and wingnut could be used to replace it, since it only needs to provide tension. Sheer strength is provided by the bushes, which also hold the tension of the counterbalance spring.

August 13th, 2012, 08:51 AM
Say, just curious if you happen to have a spare 15" LCD? I've got a 15" iMac G4 that's in good enough shape for me except for the screen being pretty dinged-up...

August 13th, 2012, 04:32 PM
Say, just curious if you happen to have a spare 15" LCD?

PM'd you on that..