Q: iMac G4 17" White/Gray screen problem
Hi All,
I am collecting and repairing old Macs and I just got an iMac G4 17" from eBay few days ago. It was marked as non-working machine with a power supply problem. I have fixed the issue with the power supply (few capacitors had to be changed) and now I'm facing to the next problem, and there I need your experiences:
The iMac boots nicely but the 17 inch flat screen just gets the electric power - no graphic signal. It displays just a white screen.
If I connect an external monitor I can see everything working fine. I can go the the System Preferences and there I can change the different settings of BOTH(!) screens. If I change the brightness of the "iMac Display" then it goes darker or brighter. If I change the resolution from 1440x900 to something else then it goes "off" and then comes back but still with the white screen. If I change something again then it will goes "off" and then get the new resolution but still displays the white screen. Looks everything fine but no graphic display just a white screen.
What could be the problem?
I think the GPU is OK because it would not have picture on the external monitor.
I think the LCD is ok as well, because I can change the brightness and if I change between the resolutions then it does something...
When it boots it displays white screen on the LCD and on the external monitor too. After the boot it loads the Mac OS X 10.5 and then the external monitor displays the "real" screen.. but I can not see the gray Apple logo on grey background on any display before my "desktop" comes on the external monitor.
Few more information about this poor iMac:
- I think it was already opened few times because the bottom disk plate says it sould be an iMac G4 17" 1,25Ghz with a serial number W8******PJH but if I'm going to check this in the About this Mac window it tells me it is an iMac G4 17" 1Ghz model with the SN: W8******SD3.
- I am not sure the LCD with the neck belongs to the "logic board" or to the "bottom disk plate"
I have already checked many posibilities to find out what could be the problem and now I'd like to ask you too.
I have no problem with soldering or replacing components...
Thank you in advance,
Attila
<Edited By Host>
iMac, Mac OS X (10.5), iMac G4 17" 1Ghz, 1GB RAM
Posted on Aug 18, 2013 10:34 AM
Hi,
Just to reply to my own post and let other to know what was the problem:
Well, I bought a new neck what is for an iMac G4 1Ghz and find also an LCD what is for the same model.
After spent hours and hours with multi-meter and signal measuring with oscilloscope I find the LCD is wrong.
I did test from the GPU till the end of the cables up in the "head" and till this point everything was okay..
Actually the original screen of my iMac is one of the bad series from the iMacs, serial numbers starting with W8... This series has a production failure on the logic board of the LCD! Wrong (too thin) soldering on few of its components.
Knowing this issue, I decided to replace the LCD itself instead of repaire the bad LCD electronic board. Could be very complex to resolder each connections.
If any has same kind of problem with an iMac G4 and the serial number starts with W8... then follow this troubleshooting steps:
1.) access an external monitor to be sure the GPU works properly (rarely goes wrong, if yes, Logic Board failure: replace it. tip: eBay)
2.) open your iMac, disconnect the neck cables from the Logic Board and open the head, remove the LCD and test the neck cables and connectors with multi-meter. Many times during the years the neck cables breaks inside the neck and then has mis-connections or totaly "no connection", if this is your problem: replace the neck or if you're hardcore electric hobbiest replace the cables only. tip: eBay
3.) if both of the previous checks did not point to any failure then probably your LCD has the problem. It is very difficult to repaire, maybe impossible. Replace it. Be carefull: iMac 15" and early 17" LCD are different than late 17" and 20" LCDs. Be sure what kind of you have and buy the correct replacement component. If you have mixed them up, then you'll have lot of trouble with the neck cables/connections and Logic Board GPU connector pinout...
Hope it helps,
happy repair,
cheers
Attila
Posted on Oct 29, 2013 2:38 AM