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iMac DV 400 ps problem

Maconthemove

Well-known member
Got two iMac DV 400 computers with dead power supplies. Will power supplies from iMac 233 or 266 work in the newer model?

 

funkytoad

Well-known member
That is a good question. I have been searching to find an answer to that. No luck yet, but I will let you know if I find something.

 

Maconthemove

Well-known member
Doing a little googling, it seems there is two ps groups. the 233-333mhz and the 350-700mhz group. Maybe some one knows something about imac ps.

 

iMac600

Well-known member
The 233-333mhz iMacs are Tray Loaders. The PSU from a Tray Loader generally doesn't fit a 350-700mhz Slot Loader.

 

phreakout

Well-known member
It could very well be the PAV board is bad (Power Analog Video).

If you look straight down from the top mid-rear of the iMac, right where the small holes are located around the handle, you'll see the the electrical cord's connector is attached to the big circuit board underneath the picture tube (CRT). THAT circuit board IS the PAV. It is essentially the main bridge of electrical power for the iMac; It suuplies power to the logic board, down convertor board and picture tube.

This is a common problem in CRT-based Macs. One way to tell it's nor working is after adding power to the iMac, it tries to turn on for a second, but shuts off. Also, a high pitch whine coming from the inside the computer. A new board will cost around $300-$400 USD, not including labor and tax.

It could also be the down convertor board that has gone bad.

This small board is attached to the logic board and PAV board, located underneath the iMac. It is there to supply low-voltage to the logic board and also to the hard drive. I'm not sure how much a new board costs, but I know it's much cheaper than a PAV.

The logic board could also be faulty. This one is obviously located underneath the iMac. This is another part known for failure, but on a rare occasion. This board, like all other logic boards, detect when the power button is pressed and runs a quick POST test (Power On Self Test). The cost to replace a logic board is fairly expensive, around $400 to $600 USD. At those prices, I would just opt to replace with a newer Mac.

73s 8)

 

MacTCP

Well-known member
I have 1 spare 500mhz iMac G3 down converter (which would work in a 400mhz too), if you need one. I also have a whole upper 500mhz iMac G3 which should contain a PAV board. (I don't want to get the PAV out myself because it's so close to the CRT)

If you need something, I might be able to help you.

 

Maconthemove

Well-known member
Just plugged in the imacs. Blue imac powered up when I lifted the back end up. There was a long beep than silence. The power button was lit up and it did nothing.

Pink imac does nothing at all.

 

MacTCP

Well-known member
Beeps usually have something to do with RAM. You should open the coinslot on the bottom of the iMac to see if there is RAM and if it is in correctly.

 

Maconthemove

Well-known member
Good call MacTCP. Reseated the ram and no more beep. Noticed that pink imac had no battery. Would that cause it to not start up?

 

MacTCP

Well-known member
Noticed that pink imac had no battery. Would that cause it to not start up?
It doesn't seem likely that a battery would cause something that big, but I think it would be worth a try since you can often get them cheaply from online stores. Sometimes weird things can happen because of batteries.

 

phreakout

Well-known member
Actually, something as simple as a PRAM battery can be startup related. It could cause the Mac not to start up at all or even power on.

Remember, the battery powers the PRAM, Power Management Unit (PMU/CUDA) and detection for power button. When that battery goes dead, the PMU/CUDA gets corrupted and loses its sync with the rest of the Mac. The PMU/CUDA isn't just a chip; it's an entire computer on a chip.

73s 8)

 

Maconthemove

Well-known member
Tried resetting the cuda switch on both blue and pink imacs. No success.

The pink is dead and the blue starts up,then chimes, then just sits there with the power switch light pulsating. Going to find the service manual.

 

equill

Well-known member
Tried resetting the cuda switch on both blue and pink imacs. No success.The pink is dead and the blue starts up,then chimes, then just sits there with the power switch light pulsating. Going to find the service manual.
When you do find it you will discover that the PMU takes more than a prod at the button to reset it. The PMU is a computer within a computer, and it repays extreme care, electrostatically, when you are near it.

Having taken the bottom off the iMac while it stands on its display face, reconnect the power cable to a switched off and grounded power outlet. Remove the battery and wait 10min. (10min is overkill, but you need to be sure that you have reset the logic board by removing all power for long enough.) Install a new battery, but ground yourself on the RFI cage before you do so. Touch no part of the logic board other than the battery cage during this process. With the cap end of a ball-point pen, or similar, press the PMU switch once, and only once (ie, no bounce) for a second or so. Reassemble the iMac and power up. If you still get no startup, you will have to start on the real bit of diagnosis.

The first part of that will be to confirm that all the internals are present.

de

 

Maconthemove

Well-known member
Bought a new Pram battery. 3.63V Pink computer is stone dead. Blue computer still powers up, hard drive and dvd drive spins. Powers down. It does not shut off, seems like going in to a sleep mode.

 

phreakout

Well-known member
Bought a new Pram battery. 3.63V Pink computer is stone dead. Blue computer still powers up, hard drive and dvd drive spins. Powers down. It does not shut off, seems like going in to a sleep mode.
Try reinserting the battery, press the PMU/CUDA button once for 1 second. Next, turn on the blue iMac and immediately press and hold down Apple (CMD) + Option + Letter P + Letter R. You'll hear the startup chime for 3 chimes. Then, immediately press and hold Apple (CMD) + Option + Letter O + Letter F. This will put the machine into "Open Firmware" mode.

Enter the following:

reset-nvram (hit Return)

set-nvram (hit Return)

reset-all (hit Return)

The iMac will reset and you should hear the startup chime one more time.

If this doesn't work, then it could be a problem with the PAV board, logic board or bad RAM. Try a different RAM to see if things improve, first. If not, try installing an identical logic board from a spare machine. If you get the same results, it's most likely the PAV board.

73s 8)

 
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