Hello Jim, I have just completed a visual inspection to the video cable from the logic board only, and everything looks good. (2 weeks ago I replaced the inverter, and inside the monitor it looked good too). I then read the following from an iMac service manual under the troubleshooting section, and I think I am under the point # 5:
Check for external video. Connect an external monitor to the mini-VGA port. If you don’t have external video, replace the main logic board. If you do have external video, go on to the next step. Anyhow, either replacing the neck extension or the logic board, it is too expensive for me, and I have actually browse a website where I can buy an used working iMac G4 20" for about 500 USD. But not I live in Italy, maybe one day I will see. thanks again for all of your support. take care carlo On Aug 31, 7:23 pm, Jim Scott <[email protected]> wrote: > > On Aug 26, 7:07 pm, Jim Scott <[email protected]> wrote: > >> On Aug 23, 2010, at 11:27 AM, pink74slk wrote: > > >>> I have an iMac G4 USB2.0 and the monitor does not lit anymore. > >>> I replaced the inverter and still the same black monitor. > >>> I then have bought the cable VGA adapter and connect the iMac to my > >>> TV, and here the facts: > > >>> just keep in mind that after the backup I did, I formatted the HDD > > >>> so > > >>> if turn on the iMac, the TV will be black as well, no signal > >>> transmitter > > >>> instead > > >>> starting up the iMac from the boot DVD Leopard, the TV monitor is > >>> white. > > >> Carlo, > > >> A white screen means that the screen is getting power, and that your > >> inverter is OK. However, your screen is not getting data, which means that > >> there's a problem in the circuit from your logic board video cable > >> connector to the LCD. The most likely problem is that the video cable is > >> not properly connected to the logic board, or to the LCD, or both. > >> However, if the cable is securely connected to the logic board and the > >> LCD, the next most likely problem is a break in the video cable (also > >> known as the LVDS or low voltage data signal cable) between the logic > >> board and the LCD connector. Because of the way the cable is snaked > >> through the iMac G4's neck, which can flex and swivel, this is a common > >> occurrence. > > >> The fix is to replace the neck with a new one. If you do this, make > >> certain you get an exact replacement. There were a bunch of different > >> necks for the iMac G4, depending on screen size and logic board/cpu > >> version, so be careful. Just any old iMac G4 neck may not work. There's a > >> tag on the cable, which will require an Apple Service Manual to decode, > >> that identifies the neck in your machine. It's on the logic board end. > >> Match the code on that tag, and you've got the right neck. > > >> Aren't iMac G4s such sweethearts to work on? No wonder Apple moved on to > >> the current cantilever pedestal AIO flat panel form factor rather quickly. > > >> Jim Scott > > On Aug 29, 2010, at 6:36 AM, pink74slk wrote: > > > Thank you Jim, > > > please correct me if I did not understand your explanation. > > The LCD monitor of my iMac G4 never turns white, it always remain > > black since the failure happened. > > The only "white signal" is on the TV screen, when booting up from DVD > > Leopard, and the LCD it is slightly black. > > > Any more insights, or what you told me earlier is still applicable? > > thank to you and everyone is contributing/commenting. > > > regards, Carlo > > Carlo, > > Let me try again. A white screen with no data almost always means the > inverter is getting power and illuminates the screen. No data on the screen > means the data signal cable isn't working -- it's broken internally or > disconnected or not connected properly. > > From your description, you've got a problem with the low voltage data signal > cable not delivering data to the built-in LCD of your iMac G4. I suspect the > cable is broken or shorted inside the neck. But it could be disconnected or > not connected probably to the logic board, or to the LCD itself. There also > could be a problem with the inverter cable. Have you tried shining a very > bright light on the screen after the iMac has booted? If you can see any > images -- even faintly -- that means the inverter cable has broken/shorted, > probably inside the neck > > As for your connection to the TV, it's clear that power is getting to the > screen, which is why it turns white. But the video signal or data isn't > getting there. This could be because there's a problem with the video > circuitry on your iMac's logic board, or a problem with the adapter cable or > video out port, or because the video cable to the LCD in the iMac is shorting > out the video circuitry. Or it could be a simple incompatibility between the > iMac and the TV (and you don't say what kind of TV -- flat screen or tube). > > Try connecting the video out port to a regular VGA computer monitor instead > of your TV. Borrow one if need be. If you can't get video on the monitor, > then disconnect the video cable to the LCD from the logic board, which will > require some disassembly/reassembly of the iMac. I've had situations where > disconnecting the video cable from the logic board made the external monitor > work, so it's worth a try. > > If after all of this you still cannot get a video signal on the external > monitor, then you may have a bad iMac logic board. However, based on the fact > your TV screen does go white, I suspect that your logic board/video circuitry > is OK and that connecting to a standard VGA monitor will work, which means > the no-video problem with the LCD is from the logic board end of the video > cable to the LCD itself. > > Hope this helps. It's a bear trying to diagnose this way, but I've given it a > try. > > Jim -- You received this message because you are a member of the iMac Group, a group for those using Apple iMacs and eMacs. The list FAQ is at http://lowendmac.com/imac/list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/imaclist
