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iMac G3 Slotload 350MHz No power

Daniël

Well-known member
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?!

 

Iesca

Well-known member
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).

 
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Iesca

Well-known member
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).

 
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Daniël

Well-known member
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!

 

Iesca

Well-known member
I can now confirm that all three of the iMac G3s are alive and well, but the third's revival was a bit more dramatic than the others, although it may perhaps point to the actual problem with these things (to someone more knowledgeable than myself).

It took almost a week to start up stably. When it started turning on, at first all seemed well, but then there were snaps/pops and momentary distortions in the CRT raster. I was worried something was shorting, but I never caught it visually inside and it eventually stopped. (At this point it was not reliably staying on.) However, the display would then begin to sink and distort on the screen, with horizontal worms across the whole display, lasting generally until the machine was shut off again. This too has disappeared, and everything appears to now be completely stable. I backed up the HDD, installed the original system, and updated through 9.2.2.

Before I update the firmware to 4.1.9f, is there reason to try and preserve the factory boot ROM? It's version 1.2f2, though I would have no idea how to do this.

 
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Iesca

Well-known member
Another update: the new speaker drivers I ordered on ebay arrived recently and I was able to install them successfully! (When installing any new drivers, make sure that the red wire is on the left side for each one while you face the speaker assemblies as they would be installed in the iMac, at least for the Graphite iMac G3/400 DV SE).

My only comment is that they are very loud, I had to turn the speakers down individually all the way from within the Sound control panel, otherwise, even with the master volume set to near minimum, they were quite blasting. Perhaps 4Ω is too low an impedance?

 
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CC_333

Well-known member
My only comment is that they are very loud, I had to turn the speakers down individually all the way from within the Sound control panel, otherwise, even with the master volume set to near minimum, they were quite blasting. Perhaps 4Ω is too low an impedance?
Maybe so.  I'm not super well-versed in the subject of loudspeakers, but maybe one can add a resistor of the appropriate wattage to increase the impedance to 8Ω?

c

 

belzrebuth

Well-known member
I'm already trying having the power plug connected to my G3 which is not turning on as reported ealier in this thread.
I'll update if that fixes the no power issue I'm having.
With that said a resistor won't address the impedance mismatch of the amplifier/speaker as that is relevant (varies) in respect to the frequency applied; it's not fixed.
As a load you could test an amplifier with a fixed resistor but a resistor in series with a speaker would probably alter the frequency response of the speaker.
You could try it in order to bring the volume down a bit but it's not a 8 ohm speaker; it's a 4ohm speaker in series with a 4ohm resistor.
 

dan.dem

Well-known member
As a load you could test an amplifier with a fixed resistor but a resistor in series with a speaker would probably alter the frequency response of the speaker.
You could try it in order to bring the volume down a bit but it's not a 8 ohm speaker; it's a 4ohm speaker in series with a 4ohm resistor.
Hmm. I don't see a reason why a resistor (of decent quality) should have a negative influence on the frequency response of an amplifier speaker combination. Usually a (decent) resistor has an clearly better Q-factor than a good speaker, meaning its capacitive and inductive components are negligible, hence largely independent of frequency.
Even more: In both analogue and digital amplifiers a higher resistance load makes it easier to maintain the intended wave form hence minimizing THD.
For my 1980s Yamaha amp I'm using good ceramic resistors in series to (cheapish) modern speakers (labeled as 4 Ohm but going as low as 2 Ohm in some situations - so, that's a non ohmic load!) as a temporary measure (now 2 years :unsure: ) until I find a good replacement for my old 8 Ohm Peerless.

So, @CC_333 I see no problem reducing the amp's load with a resistor in series. And an iMac isn't a high fidelity audio device, hence no worry about this. But it would be interesting to know what the original speakers impedance is. It could be as high as several tens of Ohm. Also, be aware that a good part of the audio amp's energy is now used to heat up the resistor, so without increasing the load on your iMac's amp (better not) your speakers will end being several decibels less loud than the original ones (assuming a similar efficiency of the old and new speaker). If you are tuning the resistors to a similar speaker volume like the original you may overload the iMac's audio (and you likely will encounter distortion).
 
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