[I apologize if this ends up being double posted, I originally submitted
a post similar to this one better then 24 hours ago via Google Groups
but it seems to have been absorbed by the ether. Because of this I am
rewriting and posting via my ISP's NNTP server and encouraging others to
avoid Google Groups at least until they get their act together.]

I was given a pile of parts that amounted to an Apple iMac DV 400
(http://www.lowendmac.com/imacs/400.shtml) awhile back. The guy that
gave it to me said that it didn't power up but that he had no idea why.
I know that iMacs of this vintage were notorious for blowing their PAV
(power, analog, video) boards. All the Mac people that I have talked to
say that the only way to fix it is to replace the PAV board because the
boards weren't fixable (such a typical Mac user solution). I don't want
to spend the $75 to buy a new board when I know that I should be able to
fix it with a few bucks worth of of the shell electronics.

After reassembly I plugged the unit in and hit the power button. All I
got was a quick blink of the power LED and a click through the speakers.
If I tried to turn it on again nothing would happen unless I had
unplugged it for a few minutes. The same thing happened when I tried
using an external monitor (this model has a standard 15 pin VGA
connection on the back) so I doubt that the flyback is the culprit.

Next I disassembled the unit to get a better look at the PAV board. I
carefully inspected it for cold solder joints and the like. I've seen
better PCB manufacturing but all in all everything looked okay. One
thing did jump out at me. The top of the large 560uF 400V capacitor
designated C905 on the PCB was domed (out not usually a good sign).
Unfortunately I don't have a ESR meter so I am unable to verify that it
is bad. Is there anyway I can test this cap without an ESR?

With my hypothesis about the capacitor I search the web for "imac" and
"C905" and found a page
(http://homepage2.nifty.com/tamaru/iMacDV/iMacDV_1.html) where the
author seems to be documenting the same problem although I can't be sure
as it's all in Japanese. On this page there are also a number of
pictures of a power IC that on my board is labeled as IC901. It would
appear that this is a Fairchild KA5S12656
(http://www.fairchildsemi.com/ds/KA/KA5S0965.pdf).

Does anyone have any experience working on these iMacs? Will replacing
the cap and/or the power transistor get this beast up and running again?
Any thoughts on where I can find the Fairchild part cheap (Digi-Key
doesn't list it and I doubt that Fry's or Radio Shack are going to stock
it). I'd love to find somewhere in the Portland, Oregon metro area that
stocks it or is able to get it easily (and inxepensivly).

--adam

Hi!

Have you checked to see if the clock battery is any good? (You'll find it
when you open the memory door at the bottom center of the computer. It's up
back by what I think is the graphics processor.

If that battery is dead, the system will not power up reliably or at all. I
had the exact same problem with a 2001-model iMac (DV model? Dunno, it has
firewire...) and found that replacing the clock battery fixed the problem.

If memory serves, the batteries are about $15 from an Apple dealer, maybe
less if you shop elsewhere.

William

Thanks for the reply William. I forgot to mention that I did check the
battery. It was only putting out a third of a volt compared to the 3.6
it should. Not wanting to spend $15 on a new battery I pulled the
battery out of my cell phone, soldered a couple of leads to it and
connected connected it to the terminals (whatever works). Unfortunately
it didn't help. It still only blinks for a half second or so the first
time I hit the power button.

--adam

On Wed, 15 Dec 2004 05:30:31 GMT, Adam wrote:

Thanks for the reply William. I forgot to mention that I did check the
battery. It was only putting out a third of a volt compared to the 3.6
it should. Not wanting to spend $15 on a new battery I pulled the
battery out of my cell phone, soldered a couple of leads to it and
connected connected it to the terminals (whatever works). Unfortunately
it didn't help. It still only blinks for a half second or so the first
time I hit the power button.

--adam

These imacs will work with a dead battery.

That capacitor is certainly worth checking, but it's not unusual for
some caps to have a plastic insulator on top which domes out when the
shrink tubing is put on. If it has such a plastic insulator, try
cutting it off to see if the actual metal can is bulging out. If the
can looks fine, the cap is probably ok.

The big problem I've seen with these is due to an interaction between
mac os 10.3 and the original firmware. It causes all kinds of
problems with the built in display and even causes it to shut down if
it gets bad enough. It should power up for about 5 seconds though if
this was the problem. This fix for this is to update the firmware if
you can get it to boot.

It does sound like a problem with the monitor/power supply board. I
would try it with everything unplugged such as the hard drive,
DVD-ROM, and RAM just in case one of these id drawing too much
current.
Andy Cuffe

Andy Cuffe wrote:
On Wed, 15 Dec 2004 05:30:31 GMT, Adam wrote:

Thanks for the reply William. I forgot to mention that I did check
the
battery. It was only putting out a third of a volt compared to the
3.6
it should. Not wanting to spend $15 on a new battery I pulled the
battery out of my cell phone, soldered a couple of leads to it and
connected connected it to the terminals (whatever works).
Unfortunately
it didn't help. It still only blinks for a half second or so the
first
time I hit the power button.

--adam

These imacs will work with a dead battery.

That capacitor is certainly worth checking, but it's not unusual for
some caps to have a plastic insulator on top which domes out when the
shrink tubing is put on. If it has such a plastic insulator, try
cutting it off to see if the actual metal can is bulging out. If the
can looks fine, the cap is probably ok.

The big problem I've seen with these is due to an interaction between
mac os 10.3 and the original firmware. It causes all kinds of
problems with the built in display and even causes it to shut down if
it gets bad enough. It should power up for about 5 seconds though if
this was the problem. This fix for this is to update the firmware if
you can get it to boot.

It does sound like a problem with the monitor/power supply board. I
would try it with everything unplugged such as the hard drive,
DVD-ROM, and RAM just in case one of these id drawing too much
current.
Andy Cuffe


I've worked on these and have some info on them. Contact me off board
and I will foreward it to you.

Richard

If you can get a whole PAV board for $75, I say do it! I think I paid $150
to Microdoc in Eugene aafter dinking around replacing caps and
resoldering. I can't say for sure if the PAV board is your only problem.

In article t,
Adam wrote:
I was given a pile of parts that amounted to an Apple iMac DV 400
(http://www.lowendmac.com/imacs/400.shtml) awhile back. The guy that
gave it to me said that it didn't power up but that he had no idea why.
I know that iMacs of this vintage were notorious for blowing their PAV
(power, analog, video) boards. All the Mac people that I have talked to
say that the only way to fix it is to replace the PAV board because the
boards weren't fixable (such a typical Mac user solution). I don't want
to spend the $75 to buy a new board when I know that I should be able to
fix it with a few bucks worth of of the shell electronics.

After reassembly I plugged the unit in and hit the power button. All I
got was a quick blink of the power LED and a click through the speakers.
If I tried to turn it on again nothing would happen unless I had
unplugged it for a few minutes. The same thing happened when I tried
using an external monitor (this model has a standard 15 pin VGA
connection on the back) so I doubt that the flyback is the culprit.

Next I disassembled the unit to get a better look at the PAV board. I
carefully inspected it for cold solder joints and the like. I've seen
better PCB manufacturing but all in all everything looked okay. One
thing did jump out at me. The top of the large 560uF 400V capacitor
designated C905 on the PCB was domed (out not usually a good sign).
Unfortunately I don't have a ESR meter so I am unable to verify that it
is bad. Is there anyway I can test this cap without an ESR?

With my hypothesis about the capacitor I search the web for "imac" and
"C905" and found a page
(http://homepage2.nifty.com/tamaru/iMacDV/iMacDV_1.html) where the
author seems to be documenting the same problem although I can't be sure
as it's all in Japanese. On this page there are also a number of
pictures of a power IC that on my board is labeled as IC901. It would
appear that this is a Fairchild KA5S12656
(http://www.fairchildsemi.com/ds/KA/KA5S0965.pdf).

Does anyone have any experience working on these iMacs? Will replacing
the cap and/or the power transistor get this beast up and running again?
Any thoughts on where I can find the Fairchild part cheap (Digi-Key
doesn't list it and I doubt that Fry's or Radio Shack are going to stock
it). I'd love to find somewhere in the Portland, Oregon metro area that
stocks it or is able to get it easily (and inxepensivly).

--adam

Hi!

Unfortunately
it didn't help. It still only blinks for a half second or so the first
time I hit the power button.

Look around the battery for a small button on the board. (IIRC it's the
"CUDA reset" button.) Push it for a short while. Maybe the dead battery
corrupted the PRAM and is keeping the machine from starting?

Worth a shot.

As far as dead batteries go, I've seen some of the iMacs I administer will
keep going, oftentimes just complaining about the clock not being set.
Others just won't start and may blink for a second or two..or even do
nothing at all when the power button is pushed. Some started right up when I
put in a new battery. Others I had to push that little button.

William

Did someone attempt to put System X in this machine? But then it should
power up but no video as he

http://forums.macosxhints.com/archiv...p/t-11411.html

These guys put an ATX power supply in one:
http://www.radiomods.co.nz/imactoatxconversion/

This is from the iMac diagnostic:
"In a No Power situation, first check for +5 V trickle power at J9
(refer to =93Testing J9 for +5 V Trickle Power on the Logic
Board=94), then check the DCO (Down Converter On) voltage on the
logic board at capacitor C10 (see figure below)"
It goes on .

Richard

Did someone attempt to put System X in this machine? But then it should
power up but no video as he

http://forums.macosxhints.com/archiv...p/t-11411.html

These guys put an ATX power supply in one:
http://www.radiomods.co.nz/imactoatxconversion/

This is from the iMac diagnostic:
"In a No Power situation, first check for +5 V trickle power at J9
(refer to =93Testing J9 for +5 V Trickle Power on the Logic
Board=94), then check the DCO (Down Converter On) voltage on the
logic board at capacitor C10 (see figure below)"
It goes on .

Richard