Saturday, September 19, 2015

Junk 2006 iMac repair - Part 1

So my father's browsing PC bit the dust. It was a 15 year old dinosaur with USB1.1, SD-RAM and a Northwood core Pentium 4. Wasted way more time trying to save it than the whole thing is worth. PSU troubles first then nothing working out right with the new (read: only 13 year old) PSU either.
Crappy Molex connectors, ancient barely functioning HDDs, etc. I gave up at the point where it became clear that money would have to be spent in order to get the thing running again. Simply not worth it.

So I went online and bought a BRAND SPANKING NEW ...

Just kidding, I bought this:

A Late-2006 model iMac A1208 (2Ghz Core2Duo, 1gig of ram, 160gig hdd)  for $30 shipped, not a terrible deal.

I was pretty confident that I could fix it up on the cheap based on some initial research.

As you can see the screen is broken but that didn't bother me since most (all?) of these were sold with defective LG displays that developed vertical lines after a few years of operation anyway.

Now you'd think you could just install another 17" panel but of course it's never that easy.

The display Apple used in the machine has a "weird" pinout. I'm not sure if there's really a standard or if it's just some manufacturers agreeing to a certain pinout a few years after this machine was released but the majority of compatible displays will have a pinout that's different from the iMac's.

Since most of these machines developed vertical lines and most readily available displays couldn't be used with them an opportunity presented itself for anyone willing and able to design an adapter and so the UniMac was born.

The thing is a pin-swap board that lets people use the original LVDS cable with the new "standard" pinout displays. It also includes an 24C02 I2C eeprom that spoofs an original display's EDID for the firmware (you didn't think Apple would just let you swap parts out like that did you?)

In addition the onboard eeprom also enables using newer displays that don't come with an EDID eeprom at all.

That said...

IF your replacement display has an EDID eeprom then (even though the firmware will reject it) it will work once the machine is booted.. at least with the discrete graphics model.
What this means is you won't get the Apple logo or any other output from the firmware (boot menu, firmware upgrade screen, etc..) but it will work fine within OSX as well as Bootcamp, even in text mode.

If the Intel graphics model doesn't want to work this way or your display doesn't have EDID at all (or you're just really keen on getting video output from the firmware) then you need to get a 24C02 (24C01 might work too) eeprom loaded up with the original display's EDID data and hook that up to the appropriate pins.

The EDID data from my broken display for reference:

Also, if you DO have EDID but want to be a perfectionist you could try to find the part the firmware looks for and merge only that with the original EDID data of your display. I'm not sure if it actually makes a difference or not.

Now luckily the original connector has all of the pins in it (ie. it's not the type where unused pins are missing) which makes it ideal for a DIY conversion. So that is what I attempted.

The metal casing is attached to the connector with a few tabs and some glue but you can tease it apart with tweezers.

There's hot glue at the base but it doesn't adhere to much. You can just push it down the wires.

This part it finicky and requires a lot of patience and several different tools. The center part slides out. 

Slowly and carefully..

I'm sure there's a production jig/machine for this connector that pushes it together. It's really not made to be disassembled again so just keep that in mind and treat it accordingly. It took me about 20 minutes to pull it apart.

Pin-swap time!


I did solder the missing grounds afterwards and just connected them to the exposed ground lead

The pinouts are as follows:

Left is the original LG display and right is the new "standard"
Credit goes to Jim, author of じむのとりあえずやってみたの巻 who has an 8 part series on doing the same thing with no prior knowledge (in Japanese).

All wires are color coded so I've made these additional notes while doing the conversion:

Thick green wires are ground
Orange wires are +3.3V (you'll have one left over after conversion)
Black is DDC Data
White is DDC Clock
Pink is DDC Vcc

LVDS pairs are individually shielded in colored cables (peel back the black cloth-tape further if you can't see them)
These outer cable are:

Green: Even 0
Blue:  Even 1
Magenta: Even 2
White: Even Clock
Black: Odd 0
Red: Odd 1
Brown: Odd 2
Yellow: Odd Clock

LVDS inner wires: Green is POSITIVE, Red is NEGATIVE

After all that I put the connector back together and added some tape.

A drop of mineral oil on the pins helped with reassembly.

Now I just needed a new screen.

Continued in Part 2.

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