iMac G3 as display monitor (for Raspberry Pi)

[agentb]

Anyone have external VGA video hooked up to an iMac G3? My understanding is the original tray-loader iMacs have an internal DA15 that you can hook VGA up to. But the later slot loader iMacs require some sort of EDID init sequence to turn on.

I’m thinking of picking up a tray loader iMac G3 to hook up a Raspberry Pi to, thought it could be a fun machine to have.

 

[agentb]

Some interesting custom boards here along with the init sequence for the slot-loader iMac G3’s:
https://github.com/qbancoffee/imac_g3_ivad_board_init

 

[Eudimorphodon]

FWIW, the flyback transformers on all G3 iMacs (but *especially* the trayloaders) is an infamous failure point; they were blowing up back when the machines were only three or four years old. I’m curious how hard it’s going to be to find one that works.

Also of note about the trayloaders: (take this with a grain of salt, though, I got rid of mine 14 years ago… and at the time it still worked but the flyback would occasionally make loud ominous cracking noises) The internal monitors on those does connect with a Mac-standard pinout DB-15 connector, which makes it easy to connect external monitors to the iMac’s motherboard, but it’s my recollection the monitor itself isn’t a standard multisync and won’t behave with standard VGA frequencies. Again, double check this, but my recollection is it actually had a fixed line rate and changed resolutions by modifying the vertical refresh. (IE, it ran at something like 100hz in 640x480 and dropped to 70hz in 1024x768 mode). You may have to take this into account and cook up custom mode lines. I don’t know if this applies to the slot loader monitor.

 

[agentb]

Eudimorphodon Thanks for the info. Yes, reliability certainly could be a concern! From Rocky Hill's github, it looks like you need to config the RPi to "hdmi_mode" 18 = 1024x768 @ 75 Hz -- hopefully that would work also for the tray-loader iMac G3's:
Configure Resolution and Refresh Rate
-Edit config.txt

sudo nano /boot/config.txt
-Add the following to the bottom of the file and save

#iMac G3 settings
hdmi_group=2
hdmi_mode=18

 

[agentb]

I also just read that the eMac has a Sony Trinitron tube in it, so that may be more appealing -- but would require the mods used for the slot-loading iMac G3 I think to get the VGA signal connected and the monitor turned on.

 

[Eudimorphodon]

Eudimorphodon Thanks for the info. Yes, reliability certainly could be a concern! From Rocky Hill's github, it looks like you need to config the RPi to "hdmi_mode" 18 = 1024x768 @ 75 Hz -- hopefully that would work also for the tray-loader iMac G3's:

That sounds about right; again, it's been a long time but the vertical refresh rates were, like I said, somewhere around 100hz-ish for 640x480, 80-something for 800x600, and 70-something for the highest mode, so it's probably a pretty good bet the tray and slot-loaders used the same settings, or very close to it.

Unfortunately from what I've heard eMacs if anything have a worse reliability reputation than the iMacs. Another thing you need to watch out for is the plastics in all of those machines is bad; the slot-loader iMacs have the worst reputation but my tray-loader was starting to crumble to bits at the end as well. I mean, seriously, I'd almost swear that they specifically used some kind of biodegradable material instead of polycarbonate.

Anyway, I'll stop being negative(*). It sounds like an interesting project.

(* I just really came away from owning one of those things with a pretty jaded opinion of the machines, and maybe to a greater extent Apple's engineering in general around that time. Had a B&W as well and its case also just spontaneously started falling apart around its fifth birthday.)

 

[VERAULT]

i currently have 4 imacs and i just gave away an imac and an emac a few weeks back. honestly i have never seen one with a bad flyback. im not disputing you i just havent seen that particular failure yet.

 

[Eudimorphodon]

i currently have 4 imacs and i just gave away an imac and an emac a few weeks back. honestly i have never seen one with a bad flyback. im not disputing you i just havent seen that particular failure yet.

Yeah, I'm sure it's one of those things where your mileage varies drastically. My personal datapoint was I technically owned two identical (Rev. B) trayloaders which I both got for free: The one with the monitor that worked (but was starting to fail within a couple years) I got for free around its third birthday from a well-heeled coworker who's wife had a ground rule that he could buy whatever computers he wanted as long as one left for every new one added. The other came a year or so later as a box of parts from a different coworker who started a project of trying to stuff its logic board into an old Sun disk box after its monitor went boom. (But gave up/got bored, possibly after realizing that what he'd have in the end would still be a Rev. B iMac. That's what happened to me shortly after soldering together the adapter to use it with an ATX power supply instead of the big chunky original board.) Between that and word of mouth from what I can tell the attrition was really high on the tray-loaders, but, hey, I'm sure there must be some percentage of them that are still working like new.

I also had several friends and coworkers over the years complain about their slot-loaders dying, but of course you're only going to hear the complaints.

 

[Timo W.]

I own a heavily used iMac G3 with a tray-loading drive as well (from the fruit colors series). Still works fine. Like VERAULT, I never saw one with a broken flyback. Maybe this was only an issue with the very first ones?

 

[VERAULT]

I own a heavily used iMac G3 with a tray-loading drive as well (from the fruit colors series). Still works fine. Like VERAULT, I never saw one with a broken flyback. Maybe this was only an issue with the very first ones?

3 of mine are the original bondi blue 233mhz versions. I really only keep the first model... Although I have owned a couple of the other versions.