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claudiodeviaje · 04:18 PM

Detrius · Mar 25, 2004, 08:22 PM

Some people really don't listen.

The CRT can kill you. Don't mess with it. That includes taking the cover off so that you can check the fuse, which BTW would OBVIOUSLY be okay since the light turns on.

Anyway... the fact that the machine stays on implies logic board. Also, all the voltages are close enough for government work. I have never seen 24V at C10, but I'm in a 120V AC area and that may make a difference.

Connecting to an external monitor will only work if the machine is booting.

The thing that is rough is that there is a fine art to figuring out which part is bad on the first try. Unfortunately, in this case, I haven't figured that art out yet. The best way to guarantee a part is bad is to switch it out.

And again: don't try the PAV board replacement on your own. If you don't know the difference between the anode, the anode cap, the flyback transformer, and the neck off the top of your head and you can't tell me which ones have the highest voltages, then you don't need to looking at an exposed CRT. I'm not just trying to get more business for some tech. If you haven't been taught how to discharge a CRT, you shouldn't be doing it.

tooki · Mar 26, 2004, 10:16 PM

Sounds to me like it needs an NVRAM reset, first and foremost, but if you can't get to Open Firmware, there's not much you can do.

By the way, pressing Cmd-Opt-P-R resets the PRAM, not the firmware. In a New-world-ROM Mac, the PRAM is a part of the NVRAM.

tooki

bwana · Apr 6, 2004, 02:39 PM

To go to openfirmware you need apple + Ctrl + O(letter O, not zero)
If you have external harddrive with OS installed then connect it and while booting press option key. It will show all available OS you can boot from. Choose external and see whether it boots.
In openfirmare if you can go to, (white screen with several lines printed on monitor then prompt)
then type resetall enter then macboot see whetehr that boots.

claudiodeviaje · Apr 6, 2004, 03:55 PM

Thanks for the advice but it'll not work cause the computer wont boot at all!!!!!!!!!!

I just got a imac 350 with blurry monitor image really cheap and I'm going to change the parts..... I'll tell you if it works

cheers!
claudio

Wutzo · Apr 9, 2004, 11:46 AM

Did you try to install OS X without a firmware update? This kills iMacs

Pennsyjohn · Apr 9, 2004, 12:22 PM

If your iMac has the VGA connector on the back, plug in a VGA monitor and start the computer. No signal on the VGA monitor, bad MLB. Signal on the monitor, possible bad PAV board. HOWEVER, if you tried to install OS X and did not do the firmware update, go to the first CD of the install set, look in utilities, and yu'll find the update. It only runs in OS 9, but you should be able to change over using the VGA screen. Do the upgrade and PRESTO!! your screen will reappear.

claudiodeviaje · Apr 9, 2004, 12:24 PM

No, of course not. Thats why this problem is so weird....
If I'd installed Osx without the upgrade could I just follow the "reapair-procedure" that are so known in this and other Mac forums

cheerS!

claudio

murphycoverdot · Apr 9, 2004, 12:28 PM

I have seen this several times in our school district's iMacs. I used to think what is happening is that one of the drives is "stuck" and is drawing too much current, which doesn't leave enough for the motherboard... Plausible, but I have no actual evidence, and what usually works to get them started again suggests that I'm wrong.

What almost always works (except once, where the problem turned out to be a failing power supply) is to unplug the power cord for a minute or so.

The way I discovered this was that I'd disconnect the unit and take it back to my office, where it would work immediately on being reconnected. After a few times I got tired of lugging it and tried just unplugging it, and it worked.

Hope it works for you.

al

Detrius · Apr 9, 2004, 12:30 PM

Originally posted by claudiodeviaje:
Thanks for the advice but it'll not work cause the computer wont boot at all!!!!!!!!!!

I just got a imac 350 with blurry monitor image really cheap and I'm going to change the parts..... I'll tell you if it works

cheers!
claudio

The first thing, safest thing, and easiest thing to do is going to be to switch the logic boards and the down converter boards between the two machine. If it follows the pair, switch out the down converter boards. At this point, you will know if it is logic board, down converter board, or something in the display. If it's something in the display, it's 98% chance it's the PAV board.

Aric · Apr 9, 2004, 12:44 PM

hey my parents 300mhz imac just pooped out on them too. you can turn the power on but the screen stays black, never turns on. all i can do is hit the power button again and it'll turn off. this happened when they moved it from one room to another, then moved it back to the original room, so maybe all i have to do is try unplugging it like murphycoverdot said. if i have to open it up, i guess it'd be best to just take it somewhere to get checked.

keep us posted on whether you find out how to fix yours please!

macman247 · Apr 9, 2004, 06:22 PM

I've dealt with similar mischievous iMacs. My vote is Power/Analog/Video board, but I agree with Deterius in swapping out logic boards first. Beware, we aren't kidding that CRTs can kill you. Do you hear the CRT powering on/off at all? Any clicks or discharge sounds? On this model, you should hear something when the LED changes over from orange to green. Try some of the other suggestions, I'd like to know if there is a correct methodology in troubleshooting problems like this 100% of the time, I have yet to get it right...

Ecuguru · Apr 10, 2004, 01:16 AM

Same thing happened to mine, way back when, within 1 year of ownership. logic board got replaced, happy after that.

Detrius · Apr 10, 2004, 08:29 AM

Originally posted by macman247:
I'd like to know if there is a correct methodology in troubleshooting problems like this 100% of the time, I have yet to get it right...

We have run into the same problems. The service manuals don't appear to give you enough of the story to figure it out. Luckily, we happened across a machine with bad VRAM that the owner decided not to fix and then disappeared off the face of the planet. Now we have a machine that works well enough that we can swap its parts out to solve these problems.

Detrius · Apr 10, 2004, 08:33 AM

Originally posted by Aric:
keep us posted on whether you find out how to fix yours please!

The likelihood is about like this:

1 - Power/Analog/Neck (otherwise referred to as the Power/Analog/Video board)
2 - Logic board
3 - Down Converter
4 - CRT

the position of 3 and 4 is a little sketchy. I've only done one of each in the past year, while I have done numerous repairs with the same issue involving the other two.

The point is that you can't rely on what fixes someone else's problem to fix your own.

You should try resetting the PMU first, by the way.

cvtech · Apr 10, 2004, 02:59 PM

Try the unlpug option. Just unplug everything and anything that is attached to the iMac. Give it like 2 minutes or so, then try to reboot with all peripherals, USB, FW things out; this includes the keyboard and mouse.

This happened to me once or twice. The above procedure has always worked.

jpellino · Apr 10, 2004, 04:59 PM

We have 8 original bondi iMacs - two of them did this - we sprung for the $300 MLB fix on one - the other we just boot, pull the power cord, reboot, it works. For free.

When our 6100s used to do this, we knew it was pram battery time - but these don't lose time or settings - so that's likely not it.

claudiodeviaje · Apr 11, 2004, 08:53 AM

mmm that has done nothing to my imac. Its been laying in my room for the last weeks, unpluged, but still doesnt work.
My problem is not that simple. It was not solved reseting the pmu or the cuda.. I'm pretty sure that the PAV is dead...... but I'm still waiting for my "new" imac 350. The only possibility is to change the components as see whats defekt......

........... wait.............wait...........wait............
Buying in ebay can be soooooooo slow sometimes!

cheers!
claudio

gto47 · Apr 23, 2004, 06:48 PM

flyback transformer or you didn't update the firmware when you installed os x

claudiodeviaje · Apr 24, 2004, 11:48 AM

Hi everyone......
I got my new Imac 350 and testes component for component.... actually it weas quite easy.... cause the motherboard was dead.
Finally this loooong problem had an end. Now I know that I just have to buy a new mobo.....

So, What have I learned from all this odysee....... mmmm
1. Macs are a pain in the a** to repair, The case is really hard to open and if you dont have the service manual.... forget it!
2. The +24,8 V in the Mobo were acttually TOO much. eventhou it didin't seem to be that bad.
3. replacement parts are really hard too find....and if you have lunk and find one, its going to cost you probably morge than your imac!
4. this forums help quite a lot!

Thanks to everyone that replied to my question!
cheers.......

claudio