iMac G4 sunflower not starting - power button or power supply?

[paardenkapper]

Hello fellow mac enthusiasts. I hope that you may help me with my recently purchased sunflower/lamp Mac G4.

I bought it for cheap from a seller who stated that the mac was running until recently and just would not start anymore.
With a little experience with Intel iMacs I thought this might be a nice project.

When I took it home I hooked the mac up to a power outlet and pressed the start button - nothing.
As I read in some forums the power supply does fail a lot in these iMacs and this would be noticable by a clicking noise from the device, but there was no noise whatsoever.

So I took it apart.

The PRAM battery held 3,2 volts and is about 11 years old. I ordered a new one but I am still waiting on it.

One thing I noticed when inspecting the power switch was, that it seemed to be loosened - everytime you press the power button basically the whole button just moves and I am not sure if the button even does anything at all. I think the previous owner might have pressed really hard on the button plus due to heat buildup the solder pads might have come loose.

I even pulled out the drive cage and inspected the power supply for obvious leakage of caps but I could not find any.

Which brings me to the following questions

a) Does the button actually close or break a circuit on the board?
b) Can it be resoldered, has anybody done this before?
c) Is the PRAM batt charge of 3.2 volts enough for the iMac to start or should it be replaced in any case
d) Can I somehow test the power button with a multimeter before and after soldering?
e) Can I make sure the power supply is working correctly to rule out any other possible faults?

Thank you so much in advance!

 

[Dronecatcher]

This might be of some use:

Broken power button on iMac G4 - Apple Community

discussions.apple.com

Maybe remove the switch and test to see whether it functions - I suspect it's not just a simple on/off circuit?

I've found that most Macs will work without a PRAM battery and some will get upset if I dying battery is left in - there's also the PMU (Power Management Unit) to contend with which can throw a spanner in the works! Good luck.

 

[Needleroozer]

Hello fellow mac enthusiasts. I hope that you may help me with my recently purchased sunflower/lamp Mac G4.

I bought it for cheap from a seller who stated that the mac was running until recently and just would not start anymore.
With a little experience with Intel iMacs I thought this might be a nice project.

When I took it home I hooked the mac up to a power outlet and pressed the start button - nothing.
As I read in some forums the power supply does fail a lot in these iMacs and this would be noticable by a clicking noise from the device, but there was no noise whatsoever.

So I took it apart.

The PRAM battery held 3,2 volts and is about 11 years old. I ordered a new one but I am still waiting on it.

One thing I noticed when inspecting the power switch was, that it seemed to be loosened - everytime you press the power button basically the whole button just moves and I am not sure if the button even does anything at all. I think the previous owner might have pressed really hard on the button plus due to heat buildup the solder pads might have come loose.

I even pulled out the drive cage and inspected the power supply for obvious leakage of caps but I could not find any.

Which brings me to the following questions

a) Does the button actually close or break a circuit on the board?
b) Can it be resoldered, has anybody done this before?
c) Is the PRAM batt charge of 3.2 volts enough for the iMac to start or should it be replaced in any case
d) Can I somehow test the power button with a multimeter before and after soldering?
e) Can I make sure the power supply is working correctly to rule out any other possible faults?

Thank you so much in advance!

View attachment 2186065

a.) The power button is a normally-open momentary switch. There will be two small pins coming off the back of it that are internally connected when you press the button.
b.) It looks like a few of the mounting tabs of the power button have come off the circuit board. These can be resoldered, but you’ll need a relatively powerful soldering iron to heat up the ground plane to which those tab attach. You’ll also want to be careful not to melt the plastic of the button itself.
c.) I would think that ought to be fine.
d.) You can definitely test it, although it looks like more of a structural problem than an electrical problem to me. Measuring across those two pins in back in resistance mode should indicate an open circuit (often notated as 0.L for overload on the meter screen), and pressing the button should indicate close to zero Ohms. You can also do this test in continuity mode, if your meter has one.
e.) You could unplug the power supply from the motherboard, plug it into the wall, and probe the output connector for the standby 12V rail. Obviously you’d need to be a little careful since this involves mains power, but the output connector should be totally safe.

 

[paardenkapper]

Much appreciated. Thanks for the swift reply! I actually read the entry in the apple forums but my experience with that board is mostly: your mac is old, get a new one. ;-)

I will definitely test the iMac without PRAM battery but as I already removed the mainboard I will try and resolder the frontal solder pad. And with a magnifying glass I was able to see the two pins in the back which I don't think are damaged yet the power button is lacking resistance to the push of the button from the case when pressed.

Unfortunately it seems you cannot run the iMac with the lower part detached.

@Needleroozer Where exactly would I measure the 12v rail on that board. I am kind of hestitant to have it plugged into the mains power with the lower part separated.

 

[paardenkapper]

Just a quick update: I managed to solder the the button back to the pads and tried my luck - still nothing.
Not even the slightest twitch.

I even tried the hairdryer method with the PRAM battery removed.
So I guess the new PRAM battery won't change much. Probably the board or psu is fried?

 

[OldMacs4Me]

The very first thing I would check is the PRAM battery, Accessible via the RAM door. It is probably dead as a doornail and can prevent this era computer from booting.

 

[paardenkapper]

I fondly remember my PowerBook Titanium denying any signs of life with a drained PRAM battery. So maybe you‘re right.

I keep you posted as soon as the battery arrives at my doorstep.

 

[NSMacGuru]

A machine of that vintage is also prone to capacitor leakage. Might need to be recapped.

iMac G4 recap

After seeing some nasty caps on a beige G3 Power Mac, I decided to open up my beautiful iMac G4 and check the caps. A quick visual inspection looked good, but you know what can lurk beneath. I removed a few of the SMDs and sure enough... While there wasn't any liquid on the board, there were...

68kmla.org

 

[paardenkapper]

Thanks for the reminder - I looked for obviously damaged or bloated caps in the power supply as well as the motherboard but it looked really clean and nice. Aside from that I am clearly not an expert in electronics and it seems that spare parts are hard to come by.

 

[Needleroozer]

@Needleroozer Where exactly would I measure the 12v rail on that board. I am kind of hestitant to have it plugged into the mains power with the lower part separated.

I was saying to unplug the motherboard from the power supply entirely and measure the ends of the pins in that connector, although that does require you to be comfortable with plugging it in while the iMac is split open.
This pinout from the classic DremelJunkie site indicates that all the yellow wires should be providing 12V automatically:

The 17" iMac G4 Native PSU

Introduction While I have not hooked the native PSU up to a mod and there is one wire that I do not understand the purpose of, I have...

www.dremeljunkie.com

And with a magnifying glass I was able to see the two pins in the back which I don't think are damaged yet the power button is lacking resistance to the push of the button from the case when pressed.

If it doesn't feel like the button is clicking over-center when you press it, it might be that the metal membrane has been damaged and therefore the button would probably need to be replaced. If you could test those two pins in the back with your multimeter, that would provide conclusive evidence of whether the button itself were fine.

 

[paardenkapper]

Thanks @Needleroozer - I finally had some kind of progress here.

At first I opened the iMac with the power cord connected and tried measuring the 12v rails as described above: NOTHING.

But I got curious and put back in the PRAM battery and the power connector to the board and connected the power cord again. Now I can clearly hear a ticking noise from the power supply - so this is faulty.

I found another thread from 2017 where a possible repair was discussed but this is clearly not feasible for an amateur.

https://forums.macrumors.com/threads/non-working-imac-g4-power-supply-possible-to-repair.2084739

Bringing out the hairdryer again also made no difference whatsoever.
Should I give up now?

 

[TheShortTimer]

I found another thread from 2017 where a possible repair was discussed but this is clearly not feasible for an amateur.

https://forums.macrumors.com/threads/non-working-imac-g4-power-supply-possible-to-repair.2084739

Why do you think it's not feasible for you - is it because soldering work is involved?

Should I give up now?

Personally, I wouldn't give up if it's because you think soldering is beyond you. Anyone can do it.

 

[paardenkapper]

Why do you think it's not feasible for you - is it because soldering work is involved?

No, because in the linked thread the OP stated that a controller chip might be faulty.
Removing chips is beyond my abilities - I admire guys like dosdude but I know my boundaries.

Personally, I wouldn't give up if it's because you think soldering is beyond you. Anyone can do it.

I already soldered the power button back to the mainboard. Low voltage repair is alright with me but when it comes to high voltage as possibly burning our house down I'm kind of hestitant.

Thank you for encouraging me anyway. Maybe someday I come along an iMac with a broken screen and can merge 2 broken ones into a working one.

 

[Needleroozer]

Thanks @Needleroozer - I finally had some kind of progress here.

At first I opened the iMac with the power cord connected and tried measuring the 12v rails as described above: NOTHING.

But I got curious and put back in the PRAM battery and the power connector to the board and connected the power cord again. Now I can clearly hear a ticking noise from the power supply - so this is faulty.

I found another thread from 2017 where a possible repair was discussed but this is clearly not feasible for an amateur.

https://forums.macrumors.com/threads/non-working-imac-g4-power-supply-possible-to-repair.2084739

Bringing out the hairdryer again also made no difference whatsoever.
Should I give up now?

That’s a shame - component-level diagnosis and repair on high-voltage stuff is definitely higher-stakes, and I tend just to check for blown fuses or rectifier diodes rather than getting into the minutiae of the switching circuitry.
Sometimes these power supplies pop up on eBay for not too much, so swapping the power supply out may also be an option depending on the selection where you are.

 

[paardenkapper]

As some sort of last resort I wrote to an independent Apple repair provider in my greater vincinity. If he can offer me a repair I will gladly pay for it. Aside I will keep an eye out for a damaged unit or even a working power supply.

If nothing works out there is still the option of upcycling it to an external monitor which I find rather intriguing.