iMac G3 Slotload 350MHz No power

[IlikeTech]

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!

[Challenger 1983]

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

[IlikeTech]

Nope, VGA port isn't populated.  The problem is the PSU won't even start up, I don't think it's a logic board issue.

[Challenger 1983]

4 hours ago, IlikeTech said:

Nope, VGA port isn't populated.  The problem is the PSU won't even start up, I don't think it's a logic board issue.

I’m going to guess it’s capacitors, I’ll see if I can find a cap replacement guide for you

[Challenger 1983]

I couldn’t find anything regarding a capacitor replacement guide unfortunately, it seems PSU failure is common on these machines 

[IlikeTech]

I'm going to try heating the board up with a hairdryer, I can see if getting things warm allows it to power on.  If it does, I'll go ahead and replace the caps.  If not, It's likely the flyback and that's unobtainium unfortunately.

[CC_333]

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

[IlikeTech]

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.

[Iesca]

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 January 14 by Iesca

[bibilit]

IIRC battery not required, at least for mine.

 

Flyback issue was due to heavy use and no fan present on the design, so probably not your issue here.

[Daniël Oosterhuis]

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.

[Iesca]

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!

Edited Tuesday at 10:09 AM by Iesca
EDIT: uploaded pic, punctuation, minor edits

[Daniël Oosterhuis]

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?

[Iesca]

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!