Differences in the logicboard of iMac G4 17in 1.25 & iMac G4 20in 1.25

Here I am, specialist of weird Macs 😀

As far as I know, the boards are EXACTLY the same. Very simple : GPU, CPU, bridges, power supply... It would be different from a 1GHz and a 1.25GHz, but as I know, the iMac 20" is just a 17" iMac but with... a 20" screen.

You can try, but it appears it will perfectly works.

The RAM slots are pointed in the opposite direction for the 20" LB. That may make it impossible to have RAM in and get the lid closed. Maybe only one stick will fit. Maybe the other RAM slot would have to be modified/broken for the lid to close.
Please let us know if you can get this to work, and what the RAM configuration is.

PS. I also noticed that the bottom of the heatsinks look slightly different, and wonder if that will have an effect on how it joins up with the fan.

Perhaps the factor of one having a 130w power supply
and the other, a 190w power supply, may be important.
The larger display likely requires some more power.

According to http://mactracker.ca database, these are
different power supplies; though my reading indicates
there are a few part numbers from which to choose if
buying a reman or replacement logic board...

Some series of replacement or remanufactured last
model logic boards are swappable one way but not
as likely the other; some may have shipped with a
higher wattage power supply to satisfy both markets
at some point, since there are at least two part nos.
listed online as replacement logic boards for these.
The higher output power supply may be OK in a
low-power case, with smaller display, etc; but the
low output power supply equipped board may be
inadequate for the 20" given original specifications.

Elsewhere in the past few years, a similar discussion
has taken place in these forums; so one has to be
careful to have the correct power supply. Error on the
side of having the 190w unit, if you have both available.

And if the slots and openings in the case match the
computer the LB and other parts were intended to fit.
Otherwise, it is almost too easy to get other iMac G4s
to use for frankinsense parts beasts, to experiment on.

OP: What was wrong with the first or most desired iMac G4?

Just curious...
Good luck & happy computing! 🙂

fjsdofnsjgv wrote:
The RAM slots are pointed in the opposite direction for the 20" LB. That may make it impossible to have RAM in and get the lid closed. Maybe only one stick will fit. Maybe the other RAM slot would have to be modified/broken for the lid to close.
Please let us know if you can get this to work, and what the RAM configuration is.

PS. I also noticed that the bottom of the heatsinks look slightly different, and wonder if that will have an effect on how it joins up with the fan.

????????????

Don't you mean the RAM slots are not pointed the same if you compare a 1.25GHz board and a low end logic board (700 and 800MHz) ?

I never heard such a thing ; the G4 body is exactly the same for both models, from 700MHz 15" to 1.25GHz 20" (27cm ball ; the faraday cage is almost the same, just two parts for the thermal bridge ; the psu insulators are indeed different as I remember). The screen size makes the neck to differ and there are several models indeed ; but the G4 ball is exactly the same.

For instance, I had absolutely no problem at all putting a whole 800MHz 17" board (with its original bottom house) to a 15" upper house. These are just the same. The RAM doesn't affect anything and I never noticed troubles about the RAM slots position : the internal components are made to fit perfect with each other and the RAM slots never moved since it would mean that Apple had to move the CD drive, so the hard drive, so the psu, etc...

Sorry. I'm way off. I was thinking G5.

Let me assure you that the board from a 17inch 1.25 is NOT compatible with the 20inch model. The video connectors are not the same (more pins on the 20inch). I had picked up in hopes of repairing a 20inch model, but quickly came to this conclusion.

Do you know how many pins are used for the 20" screen ?

How many pins there are in the logic board ? (I may mystake, but the upper neck connector used to link the 20" screen can be different from the logic board one ?)