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iMac G3 Slotload 350MHz No power


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Hi all, I'm looking at a 350MHz iMac for a friend.  It doesn't power on when the button is pressed at all.  I can hear the high voltage come up for a second, and then slowly discharge when the button is pressed.  The Power LED doesn't come on, or even flash.  I don't hear the CRT degauss.  I do hear a mild pop from the speakers.  Checking the voltages listed in the service source, I see voltage on the standby circuit, almost exactly 5 volts.  I also see voltage at the C10 cap, around -1.3 volts.  Does anyone have any ideas on what might be the issue?  Might this be a general caps problem?

 

Also, is there a way to run the logic board externally to test it?

 

Thanks!

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23 minutes ago, IlikeTech said:

Hi all, I'm looking at a 350MHz iMac for a friend.  It doesn't power on when the button is pressed at all.  I can hear the high voltage come up for a second, and then slowly discharge when the button is pressed.  The Power LED doesn't come on, or even flash.  I don't hear the CRT degauss.  I do hear a mild pop from the speakers.  Checking the voltages listed in the service source, I see voltage on the standby circuit, almost exactly 5 volts.  I also see voltage at the C10 cap, around -1.3 volts.  Does anyone have any ideas on what might be the issue?  Might this be a general caps problem?

 

Also, is there a way to run the logic board externally to test it?

 

Thanks!

Hey Iliketech, does the motherboard have a VGA port at the back?, if so you can try an external monitor to see if there’s any Image

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  • 2 weeks later...
On 11/23/2020 at 9:23 AM, IlikeTech said:

If not, It's likely the flyback and that's unobtainium unfortunately.

Well, the flyback itself may be (at least until some enterprising rich person decides to either clone it), but in the meantime, you should be able to part out the PSU/AB of an otherwise working iMac whose plastics are shattered (which, sadly, are relatively common)?  It probably wouldn't last like a new part would, but it should last long enough for your friend to enjoy it.

 

c

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  • 4 weeks later...

Well, I wound up using this machine as a CRT donor to fix his other machine that had a CRT with some deep gouges in the front glass from being set down screen side down on the ground at the dump where it was found.  That machine is a tray-loader and should be much more reliable in the grand scheme of things.

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  • 3 weeks later...

I'm having the same issue with my newly acquired iMac G3 DV SEs. I have acquired three of them that seem to have been stored for about 20 years inside of a warehouse (two in their original boxes), and which were used perhaps only a few times before being shelved.

Unfortunately, all three have exhibited the symptoms as described by @IlikeTech whereby the CRT attempts to power up, and there's a pop in the speakers, but nothing else happens. I actually have replaced nearly every capacitor in one of the iMacs for its logic board, the PSU, the downconverter board, AND the CRT board. Having done all that, nothing has changed. The same symptoms are exhibited.

I am aware that it needs a good 3.6V 1/2-AA battery in place in order to power up, which I have installed, followed by pressing the PMU (Power Management Unit) reset button (once, as proscribed by the Service Source manual). Nothing changes.

 

It seems unlikely to me that all three Flybacks would simply die, just sitting there for two decades.


Any thoughts?

Edited by Iesca
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5 hours ago, Iesca said:

I'm having the same issue with my newly acquired iMac G3 DV SEs. I have acquired three of them that seem to have been stored for about 20 years inside of a warehouse (two in their original boxes), and which were used perhaps only a few times before being shelved.

Unfortunately, all three have exhibited the symptoms as described by @IlikeTech whereby the CRT attempts to power up, and there's a pop in the speakers, but nothing else happens. I actually have replaced nearly every capacitor in one of the iMacs for its logic board, the PSU, the downconverter board, AND the CRT board. Having done all that, nothing has changed. The same symptoms are exhibited.

I am aware that it needs a good 3.6V 1/2-AA battery in place in order to power up, which I have installed, followed by pressing the PMU (Power Management Unit) reset button (once, as proscribed by the Service Source manual). Nothing changes.

 

It seems unlikely to me that all three Flybacks would simply die, just sitting there for two decades.


Any thoughts?

 

Sadly I can't help, but I do hope you find a solution. I picked up a Flower Power over the weekend which has the same problem, splitsecond of HV and speaker popping when trying to power on. I'm going to get a donor machine at some point anyways, probably a generic color like Graphite or Blueberry, to fix this one up (front is yellowed so I need better plastics as well), but I'd still like to keep the original PAV as a spare if it can be revived.

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It lives!

After cross-posting on the Mac Garden's Discord, a fellow user suggested that they had experienced the same thing, but that simply leaving the iMac plugged into the outlet for awhile seemed to resolve the power-on issue. I decided to give this a shot and, after a few days (with intermittent testing), it suddenly sprang to life today! At first it struggled to stay on past the Disk First Aid screen, but after waiting until later in the evening, it turned on—and stayed on! I've navigated around the old hard drive, even run a DVD, and it all seems to be working great. Hard drive is probably not long with us, but it works for now.

Next step will be to replace the rotten speakers, following the advice from this MacRumors thread: https://forums.macrumors.com/threads/replacing-imacg3-speakers-suffering-from-foam-rot.2156308/

 

I'm curious what is going on here, electrically speaking. As previously stated, I replaced nearly all of the capacitors (all but 3, of which I had ordered the wrong replacements), and so the idea that some sort of capacitor reformation is occurring seems unlikely to me. Does it really all come down to the PMU chip? Or is something else going on? Was it necessary to replace the caps at all? I have two more to repair, so I'm keen to know the fastest route!

20210119_040753-1-1.jpg

Edited by Iesca
EDIT: uploaded pic, punctuation, minor edits
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5 hours ago, Iesca said:

It lives!

After cross-posting on the Mac Garden's Discord, a fellow user suggested that they had experienced the same thing, but that simply leaving the iMac plugged into the outlet for awhile seemed to resolve the power-on issue. I decided to give this a shot and, after a few days (with intermittent testing), it suddenly sprang to life today! At first it struggled to stay on past the Disk First Aid screen, but after waiting until later in the evening, it turned on—and stayed on! I've navigated around the old hard drive, even run a DVD, and it all seems to be working great. Hard drive is probably not long with us, but it works for now.

Next step will be to replace the rotten speakers, following the advice from this MacRumors thread: https://forums.macrumors.com/threads/replacing-imacg3-speakers-suffering-from-foam-rot.2156308/

 

I'm curious what is going on here, electrically speaking. As previously stated, I replaced nearly all of the capacitors (all but 3, of which I had ordered the wrong replacements), and so the idea that some sort of capacitor reformation is occurring seems unlikely to me. Does it really all come down to the PMU chip? Or is something else going on? Was it necessary to replace the caps at all? I have two more to repair, so I'm keen to know the fastest route!

 

How does the "recharge" hold up? If you leave it disconnected from power for a while, then reattach and immediately attempt a power on, does it work or does it need that "recharge" again?

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8 hours ago, Daniël Oosterhuis said:

How does the "recharge" hold up? If you leave it disconnected from power for a while, then reattach and immediately attempt a power on, does it work or does it need that "recharge" again?

 

I have not tried this just yet, but I will report my findings once I do!

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  • 2 weeks later...

I have now revived a second of the three iMac G3/400 slotloaders I acquired, using the plug-it-and-leave it method as described above. The second one, not having had its capacitors replaced at all, took a little bit longer, between 4-5 days. I can't say for sure if that's the reason, but I have the third plugged in now, so we shall see how long that one takes!

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Just bought a pair the other day actually! The ones that people have linked elsewhere have angled terminals, and those won't fit inside the speaker bubbles from what I gather. Maybe should grab these too, since they only have one pair left currently...

 

I was also able to chisel off the magnetic mounts from the old speakers from one of my units, so we'll see how they fit! Gosh, they are glued on super tight! D:

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Actually, from what I read on that MacRumors thread, the back is actually held on primarily via magnetism (with perhaps some light glue to keep it from shifting around), and a gentle but firm whack of a hammer should break it loose.

 

Also, another option is https://www.ebay.com/itm/313025353556, but it appears to be out of stock at the moment.

 

The more I think of this, the more tempted I am to pull out a spare set of speakers from a Blueberry iMac (also rotted, of course), buy a set of these, and try replacing them!

 

c

Edited by CC_333
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They are indeed magnetic, but it took more than a firm whack... Definitely glued on as well, but once separated from the original speaker drivers, they should hold on to the new ones with just the magnets.

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4 hours ago, CC_333 said:

The more I think of this, the more tempted I am to pull out a spare set of speakers from a Blueberry iMac (also rotted, of course), buy a set of these, and try replacing them!

Do it!

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Here to report that my Flower Power has managed to revive itself too! Just the day I got a nicer condition, working Blueberry to fix up the Flower Power, someone in a chatroom asked me to take a video of what the FP was doing as his was having similar issues. I had left it plugged in on and off for several days, with no effect, but of course the moment the camera was rolling and I hit the power switch... it chimed and went right into its OS X Tiger install. What is causing this?!

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I really want to know too! I really feel like the PMU chip is to blame, but is it recalibrating or something? Who knows, but it really does take several days, whatever it is... And resetting the PMU by pressing that button by the RAM slots seems to have little effect, at least as far as I can tell. Currently letting the third sit over the weekend without resetting the PMU or even installing a new battery (currently empty).

Edited by Iesca
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I can now confirm that one of the iMac G3/400s that I had previously revived started right up again after several days of being unplugged. This was the one that had had most of its capacitors replaced though, so I will check the 2nd one soon to compare.

 

Meanwhile, the 3rd one has not been revived just yet, but I installed a fresh battery and reset the PMU, so hopefully that will speed things along. (It's possible it may have revived eventually without, but it has already been a few days).

Edited by Iesca
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I've had the Flower Power out of the power most nights, as it has a slight high pitch coil whine when it's off which my younger ears still pick up, and it's just on my annoyance threshold. So it's been off for several days during the night and most of the day, and it still turns on first try when reconnecting it to power. Pretty positive result so far!

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