[kwaide]

Hi there everyone.
I've got my dad's iMac.
It's an older one, Rev. A -- 266 MegaHertz, Lime Green Apple Machine.

We took his iMac to an Apple dealer and they told us the PAV board was bad. We didn't want to shell out the $300 + dollars for them to fix it, so we did research and we bought a refurbished part and replaced it ourselves (yes, I did lots of research as well regarding the charge in the CRT and we did research and we learned how to properly discharge the CRT).

Well... anyhow... we got the part and replaced the whole bloody thing.

NOW, we get a happy Mac chime, maybe some spinnage, but nothing else.
No monitor, no fan running -- nothing else is going on.b

YES, we reset the CUDA and we checked the battery. Those don't seem to be the issue. And yes, I know for a fact that I have the proper part.

WHY is the iMac not functioning? What else could be wrong? Can anyone please advise? Thanks in advance for any help you can offer. This is really bogging us down and we'd like to have the Lime Green Machine back in functioning order and SOON.
Thanks.
- Kris

[Detrius]

Okay, since you said you actually did research on how to properly discharge the CRT, I'll actually give you some input here. And at the risk of sounding like a broken record player, I am going to reiterate this for the people that haven't read it before: The CRT is a very dangerous piece of equipment that can kill you (either from the voltage or from flying shrapnel). This is not a job like replacing a logic board. This is more like climbing to the top of a power pole to fix a high voltage transformer. If this doesn't scare you, you don't have enough respect for the machinery and shouldn't be doing the repair yourself.


now, on with the info:

On the flyback transformer, there are two knobs. You can get to them by simply taking off the bottom cover. One is screen voltage and the other is focus. The voltage is the one you want to adjust. Be warned that this is a very sensitive control and can make significant changes very quickly.

In addition, make sure that all of the cables are properly plugged up. One thing to be very careful about is bent pins on the CRT itself. If you break one, you will have to replace the CRT.


As far as other parts... the Down Converter Board is notoriously difficult to diagnose when it goes bad as the symptoms are exactly like a bad PAV board or a bad logic board. The techs may have switched out your logic board with a known good logic board to get the answer. If so, the Down Converter Board is still a possible culprit. It's rare that this part goes bad, so it's very tempting to just leave it in when you are doing these diagnostics. I have only seen one go bad, but I switched out a half a dozen other parts before I figured out that it was the Down Converter Board.

You might do well to call these guys and see if they checked the Down Converter Board.

Also, it's not that uncommon to get a bad part from suppliers. How do the symptoms before switching out the part compare to after switching out the part? Also, did you match up the brand of the CRT with the brand of the PAV board? Does the PAV board have an LG/HH switch on it? Is it set correctly?


One down side of not letting the Apple guys do the repair is that you don't have access to the tools used to calibrate the display and to set the "factory settings." Your display is likely to have funny color issues that can't be calibrated out until this is done.


For future reference, CUDA is on the old machines... tray load iMac and before. PMU is on the Slot Load iMacs and newer. They aren't the same.

[gto47]

I've done this whole deal myself but at $0 expense by simply removing the AV board and placing the power supply and logic board into an ATX chassis, then hooking up an apple PNP monitor. You might try doing this yourself to try and figure out where the problem is. What typically happens with these faiulures is that the av board will try and charge up the CRT but once it realizes there is a problem with the circuit it shuts the whole system down as the power supply powers bout the crt and the logic board. The fact that it starts up at all suggests to me that the av board is not at fault because it would not start up at all before. Now you're seemingly in the GLOD boat where the system powers up but you don't get video. Down converter boards are not as prone to failure as av boards but while its a possibility, i would be more immediately inclined to say that the problem lies in your replacement of the av board somewhere. It is also improtant to note an even more complicating factor which is that different variations of CRTS were shipped in the iMacs. In the model you are speaking of which is actually a revision "C" (RA and RB were both 233mhz models differing only in the amount of VRAM on their logic boards were only available in bondi blue) The model which you speak of "Rev C" is 266mhz, contained 6mb of VRAM, and was available in 5 colors one of which was indeed lime green) All of the RA-RD systems i have worked with contained LG CRT displays but I believe that certain models shipped with Hitachi tubes which there is an adjustment for as Detrius stated. Rev "E" and later contained i believe 3 different CRT makes just for your abstract edification. Also, you might be interested to know that there has been success with simply replacing the flyback transformer on the broken av board at a cost of only around $30 USD. I've also heard of this being done on older B%W and Graphite G4 displays which were also prone to failure. Good luck on fixing this but i think your best bet is really to just hook up an external monitor to it. As detrius mentions you have to get special apple technician display calibration software to get the color setup right which is hard to come by and the internal monitor isn't exactly spectacular.
PS: this might help you out if you don't have it already http://home.earthlink.net/~strahm_s/manuals.html#imcs