A bad hard disk would not cause the video not to work. It may be the video it self but if you get nothing on an external display then the problem could be video related. Make sure its hooked up then power it on and see if that works because if it gets the chime then it is passing POST.

By video problem i take it you mean the chip on the logic board? the GPU?
Would a problem with the GPU chip affect the mini-VGA out slot as well?

Nope it would mean you have to replace the whole logic board since everything is integrated into one piece.

ack! looks like a fond farewell to my mac then and a quick call to the old insurance company! thanks for the help anyway.

My iMac screen is completely black, can’t even see the desktop with any light source shined at the monitor. Would it be safe to assume that the lcd display burned out, or should I check to see if there’s any connectors that might be messed up... or purchase an inverter?

My screen is totally black on my iMac... There’s power going to the screen, but no image whatsoever.

Hook it up to an external monitor, if it works then your back light is not working and it is probably the inverter board (cheap fix) if the external display does not work then its probably the video chipset (expensive fix). that will help you narrow it down.

how do you differentiate between an inverter being bad and a blown fuse on the logic board or corroded wires for that matter? I figured that with a blown inverter the screen would be black but you could barely make out the video being displayed, not a completely black screen.

Ack me too!!
 

I've got an iMac G-4 20" Flat panel too.
It's got a very dim blue screen, can't see any detail, but computer starts up fine, seems to ready to go to work, responsive to the mouse.
I am guessing it's the inverter board, but don't have a spare monitor to try on it (much less the VGA connector). Have done the pram/ software checks to no avail. Is there any other way to check this out.
Also, I cannot get anyone to confirm the inverter board part #, Can anyone help?
This site says it has it with the # 922-6129 : http://www.macsupportstore.com/ but when I take it a part, this number does not appear on the board. Do I have a good #?
thanks

The actual part often don't show Apple's part number, but 922-6129 is the correct inverter.
You really should verify that the video is good on the logic board by trying an external display. The adapter is exactly the same as those that shipped with any iBook, if that will help you locate one.
If an external display also does not work, then you have other (more expensive!) problems, probably a logic board. Good external video, then the inverter is a good guess. Without trying that external video, then you just have a shot in the dark (so to speak!)

A blown capacitor on the logic board will be bloated and often oxidized. So physically checking the caps will let you know.

A bad inverter board just takes out the back light, so the display still works. Shining a lamp on it or a flash light to see the desktop or hooking up an external monitor will show you that the video still works.

Does anyone have any links to schematics for the logic boards on these imacs. It seems to be a common problem with the video chip on the logic board failing. I remember seeing a post about a company that fixes this problem but alas I did not bookmark it. I think you send in the logic board , they test it then see what it is going to cost you. I seem to recall about $600 average being quoted for this service.
Stewie

Help
Can't seem to find it!!
iMac G4 20" Flatpanel inverter board p/n 922-6129
Tried:
Welovemacs.com
DT & T Computer Services
PinnacleMicro Optical Storage
TheMacSupport Store

They all list this in their catalogs, and some show stock, but they have canceled their orders for lack of stock.

Can anyone please give a lead on where one might find one? Thanks

Try BlueRaven - http://www.blueraven.com/us/Service-...OEPartNo=11133

Thanks DeltaMac, but they seem to be out of stock also. Any other suggestions??

Any local AASP can directly order the part from Apple and you can buy it direct.

DeltaMac, cancel my last request-BlueRaven had it after all. Thanks again

My 17-inch flat panel Apple iMac display just stopped working. The screen appears black but you can see the windows faintly in the background after the machine boots up.

I did some research and found that Apple has had an inverter assembly problem in the past. There is a class action recently settled on this matter regarding the Apple Studio Displays. Other Apple computer owner display complaints continue.

After taking my computer in to the "genius" bar, I was told that the problem was most likely the inverter assembly. I was quoted a cost of $39 for the part and $135 for the labor. Just today, I got a call from the Apple Store and the techician said that the problem is not the inverter but the LCD panel itself. The news was that this part was $389! With the addition of the labor, this repair would be over $500!!

Is the LCD replacement something a novice can or should attempt? Is this repair ludicrous on a machine that is four years old? Is the only option attaching a different monitor to the system? This is unfortunate considering the display is what MADE this computer!

Clearly from my research, Apple has some "display issues" that are yet to be resolved. I'd like to know if there are other iMac who have well-cared for and conservatively-used Apple computers with this display problem. Please report your iMac display problem here;-)

Any wisdom from the more technically-expert readers would be most appreciated! I would like to make a consumer suggestion: notify Apple in formal, certified letter so that there is a record of the complaint. Otherwise, we, the owners may be the ones left covering the widespread problems.

iMacowner, it is most definitely a common problem that is mostly the inverter board - a relatively cheap part to obtain. If you have any basic fixit skills ,you can do it yourself and save a lot of money.Check first as the other posts say that you do not have logic board issues . If you plug in another monitor to the VGA port via a cheap $15 adapter and it works then your logic board as well as the included graphics chip is working and it will 99% be the inverter board. If you don't get anything on the external monitor then it is either the logic board or graphics chip that's at fault which ain't cheap to fix!
Stewie

Dim Screen
 

I too have a 17" Flat Panel G4 with a recurring "won't wake from sleep" issue. As mentioned above, the screen is black but with a barely visible desktop. Tried the usual fixes. PRAM reset. System reinstall. Random success that did not last.

Found the below Apple fix of resetting the PMU. Worked for me.

I Quote Apple— In rare occasions the settings in the Power Manager may become unusable, which can result in operational anomalies with the computer. For example, your computer might not turn on, not wake from sleep, or do (or not do) other things.

http://docs.info.apple.com/article.html?artnum=95165