Is it the DCO of my IMac G3 faulty?

+hi Seong...+

WELCOME...

well, even after replacing the DCO, the logic board could still be in question...
sounds like a part here, a part there, a part everywhere... 😟

after 7 years of use, she may be a good MP3 player, back-up - Got Airport??

sorry 😟

Thanks,
den
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.
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Hey Seong,
Well before doing that continue the checks in your manual. Especially the ones on the CRT neck connection, the connectors to the upper and lower board.
I have repaired one that had a loose neck connector.
There is a common fault on these PAVs that I have found and that is bad solder connections on the flyback transformer. They look like circular cracks in the solder around the pins that connect it to the PAV board. I've seen 3 of these.
This will require removing the PAV from the divider panel. Note the warnings about the anode voltage.
Richard

Hey Seong,

I prefer to use a multimeter to test continuity connections as I may miss it by >checking using my untrained naked eye.

I use a magnifier to do that. Testing things in circuit is hard to tell what's going on. The probes themselves can cause the faults to go away.

anyway i am having fun..taking it apart to this level for the first time..really >a marvellous machine.

Are you aware of Sam's site:
http://www.repairfaq.org/sam/tshoot.htm
and I made a discharge tool using this:
http://www.repairfaq.org/sam/captest.htm

anyway i am having fun....

Yes I have fun doing this too. The iMacs are very rewarding to work on esp since the faster ones will run the latest OSs. I've also started to include iBooks in my repair schemes. There are a lot that can be had cheaply since the GPU fails. It has been a cheap fix for me but lately my guy has been sick.
Richard

Well if you're having fun

Hey Seong,

.. five faint crackling sound from the speakers... clrk clrk clrrrk clrk clrk .. >when the power button is press .. is a sign of BAD ROM.

Well as you know 5 is a sign of bad logic board but it's hard to tell since the logic board isn't getting good power.

Could a bad ROM cause a total NO POWER... blank screen, no attempt to boot?

Well if that was the case you'd expect the screen to light up since the PAV would be working properly. Have you tried hooking a VGA monitor to the output spigot under and to the rear of the iMac?

Which unit produce the voltages? Is it the DCO or PAV or Logic Board.....
... all of the four components to replace i.e. DCO, Logic Board, PAV and the >power led switch based on the symptoms described. If need be, which ones to try >first in order of probability of the component being faulty.

This is right out of the manual:
"Power is controlled in the iMac system by the power/analog
board. Once the unit is plugged in, power flows from the AC outlet
at the wall to the AC inlet on the power/analog board. From there,
the power flows through the main cable on the power/analog
board, to the video neck board, down converter board, logic board,
and all its attached components."
So the iMac is a monitor first then the high voltages in the monitor are "converted" to lower voltages so that the logic board can use them. That's why that little board is called the "down converter".
It's the PAV that fails first due to a combination of: higher voltages, heat, no fan, insulation breakdown>shorts.
I always drop the logic/DCO into another 350-400 machine taking into account the warning about the "thermal pad" on the CPU. (see "introduction") It's the most cost effective way. I have pulled and replaced the flyback (twice) but it's a pain and costs as much as a used iMac. There are 6 400s for sale in Chicago for $40 on Craig's List, complete.

Richard

Seong,

..I have tried the external monitor earlier on..and when nothing happens, I >thought how silly of me to expect anything when there is no power to boot up, no >led light, etc..it may not be so silly after all.

Well that was a shot, thinking that the failure didn't affect logic power. That happens sometime

..let me see if i can get hold of used IMac DVs in Singapore.

Actually anything from the 350 through the 700 will work. It's just that the heat sink might be different. This is from the Flower Power service manual:
"Thermal pad is used on these boards:
661-2425, 500 MHz
661-2426, 600 MHz"
So is it a 500-600? If so the heat sink might be in a different place. Don't know much about what was released in Spore? Is that a local nickname?

With your info, I now think the PAV is the most likely culprit so dropping the >logic/DCO board on another unit to test will be a good idea.

Yes certainly the cheapest way.

Richard