Rare iMac Prototype Won't Boot (Can We Fix It?) - Krazy Ken's Tech Misadventures
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- Опубліковано 5 вер 2024
- This rare iMac G3 prototype won't boot-heck, it won't even power on! Can Krazy Ken and Steve fix it? Watch the prototype "first impressions" episode ● • Insanely RARE iMac G3 ...
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@Xievva 3am here haha
7pm here
@@abhd1234 I 23:16 pm
9 am here
no ram so nothing going to happen
i recommended removing that CMOS battery get rid of it and recap capacity on mobo n put ram in slot u should be getting beep noises booting up
there is a yellow tantalum cap by the processor board where all those silver smd caps are located. Probe that with continuity tester to see if it is shorted. if you find any other tantalum caps, check them all for short. One of your rails are shorting to ground and the first logical place to check are those tantalums.
Yep, good tip.
Tant caps aren't inherently "bad" (or no worse than old electrolytics), but old Tant caps tend to get moisture ingress over the years, or just general ageing.
And that can cause an internal short, and sometimes they get a bit "explodey" the next time you try to power up the device.
Not half as bad as the RIFA filter caps in things like the BBC Micro, though. lol
Tant caps do seem to fail with a dead-short.
Oh, it's also worth saying that the overcurrent protection on some PSUs may be set to a lower threshold than others, so some will just trip (shut down) completely if there's even a minor short.
(ie. not a dead short between say a power rail and Ground, but a lower resistance than normal, causing a higher-than-normal current to flow.)
Some switched-mode PSUs will cause an audible "click" or "chirp" sound when the overcurrent protection kicks in.
There are schematics floating around for many models of iMac. It should be possible to at least get the PSU to start up without the logic board attached, so the PSU can be diagnosed separately.
It does seem like the logic board itself has a fault here, though.
Also, the continuity mode on a typical multimeter will beep whenever the resistance reading is below say 100-150 Ohms. So a beep doesn't necessarily mean there's a "short".
The power rails on some devices might give a VERY low Ohms reading, but that could be normal for that device. (eg. the Vcore power rail on a CPU, for example.)
But since the 5V rail on the prototype was showing a "short" where the other iMac wasn't, it does back up the theory that the prototype has a short on that rail. The weird thing is why the short seemed to go away when the other power filter was hooked up.
I don't know what else hooks up to that connector to know what else to test.
Good call, but with the logic board isolated from everything else, the short went away, which says to me that the short is external to the board, I’m pretty certain it’ll be something connected to one of the headers, could be any one of them which has a 12v rail connection.
I’d disconnect the power header to the drives first and check again, if the short is gone, the fault would either lie with one of the drives or the wiring harness to them.
@@Si1983h Yep, I only realized that only after watching the video for a second time (the other day). hehe
It was a bit confusing as to which parts they were testing when they spent a while looking at the power filter, and not just testing the logic board with the drives unplugged first.
(and swapping to the other known-good logic board, etc.)
So yeah, it might be a simple fault with the power to the HDD or something.
The fact the short completely went away, and the resistance was quite high after unplugging everything from the mobo was the smoking gun. I just didn't spot it at first, due to the way the vid was edited.
I also now don't think the power filter has a problem. It's pretty much just a big common-mode choke, and the windings look pretty thick.
Although you can get a lot of current on some of the lower-voltage rails, I wouldn't have suspected a chunky inductor to be the first thing to fail, although anything's possible, ofc.
God, i remember "volunteering" to help my 7th grade teacher clean out the bookmarks on the 3 of these (dark blue, or was it more indigo?) and that's how I ended up being an IT guy for like 3 years when I was 12/13/14 (i swung by a couple times when I was skipping school in 9th)
I was an IT guy at my middle school too, I’ve fixed more projector problems than the actual IT guy has before
@@JohnMackweb same 😂
Still am honestly
Same here. I was the "apple tech" for my middle school and was paid by the schol district at 13-14 for a bit. Pulled out of class to fix computer issues. Man it was the life lol. Now I'm a windows and Linux sys admin. I know how to use apple devices but am not an apple fan.
Try disconnecting or replace the harddrive and CD-ROM drive. I have seen the PCB part of a IDE drive that failed and created a short.
This. The short was present with the drives connected and wasn't with the drives disconnected.
Yeah my first thought would be that the short came from the hard drive as well.
diodes, just dealer desolder those
i fixed an emac by desoldering the filter cap across the 12v molex input (it failed dead short)
We did try this (and a ton of stuff!), it just didn't make it into the final cut of this video. Also, the IDE hard drive worked fine in another iMac, so that kinda rules out the PCB of the Hard Drive being problematic. However, we're not done yet with this machine!...
Casually whips out the keyboard for a TAM to use on a prototype iMac
It’s the only way he can use it on a iMac, that’s why
I know this is a straightforward test, but disconnect all drives and cables (and GPU cards for those that can be disconnected), and try again. Then remove RAM and you should get the faulty or no RAM tones. If you have a faulty CPU (in any Mac) you will also get no power. These are my basic tests for any Mac.
Yes, this is what we need to look into. I have doubts that (because of the cracked connector) that the CPU card is actually making good contact with the logic board. Sadly, this may be very difficult to fix. However, it's something I'd love to look at under a microscope.
@@Mac84 You could get Ken to mail you the iMac 'pod' and you could have a look at it, but you probably need the whole iMac to really test it. Hold on, you had your iMac in the video, so you drove there? Well, it looks like you are on another trip to collect an iMac! That's if he is willing to part with it, and maybe collect some other Mac bits...
"Push the button, Frank"
ohhhhh that made me so happy lmao
.
Steve. Send the phone spiders.
DankPods viewer
I always enjoy the more chaotic episodes when something is broken and nothing seems to work, hope this will be another one of those again!
Edit: Yes it was one of those
i would actually love to see another part to attempting to try and get this up and running.
I plan to! We'll do our best! Stay tuned… ; )
try to play roblox on it
It might help to test the first indicator LED solder pads to see if it would be lit. As far as I can tell, indicator #1 says the logic board recognizes that it's getting power, which can help track down which power phase isn't completing. #2 says it's attempting to boot. A shorted connection isn't a good sign, though.
UNPLUG THE CDROM! They can short out internally! It's connected to the same power rails as the hard drive... I was waiting for you to do it since you pulled out the logic board!
iMac: *won't turn on*
iPhone 13 when the screen or anything is replaced: "First time?"
In the words of Dave Jones - the first step to troubleshooting is "thou shalt check voltages"
I'd try to powerup the mainboard in isolation from everything else, i.e with (a) bespoke benchtop power suppl(y/ies)
the dodgy connections in the processor section are also highly suspect, but if the those connections test good then there's likely a failed component on the mainboard
from that point I imagine that starting from the soft-power-on circuit and working outwards would be the best way of troubleshooting the board
How to break a old iMac with the Computer Clan (Official Video)
2:09
When you are in a group project with people you hate
another possibility (that would make other issues hard to diagnose) is that the prototype differed just enough for it's CPU-board to not work in combination with the retail version.
So you as a technician, can only figure out that 5v rail is on short and that's it? And by replacing power filter not solving problem out thats obvious, cus prot and retali was good. What about 3,3v/5v rails? What's on smc? And also chipped socket is a no no, consider to look after. Good luck guys!
I have spent literal years trying to get a mac classic Ii to work much like this process, all i ever got as a sign of life was a shock from the power board once.
its gonna have to be something that disconnected when you took it out of the chassis, dvd drive maybe? hard drive? strange question, did you try turning it on without them?
still got a blue one of these on my desk, its been changed to a sata drive after the original IDE died. working fine
Prototypes sometimes have secret power on sequences where you must complete a sequence of steps to turn them on, I have devices you even have to shake and turn upside down then power them off and turn them back on again to make them power up. I doubt this is the sequence of your mac but... there might be a power on sequence.
LOL! 9:42, _right_ when Ken pressed the power button, my phone alerted of an upcoming appointment. My alert sound? The Macintosh boot chime. "Hey, it wor-oh, no, that's just my meeting, not in the video."
Holy frick
So, I am troubleshooting similar power-on issues for a G3 iMac and found the service manual you mentioned. I found the service page that talked about checking to assure power flow is correct. I had to double take, because the manual actually says this: "With one hand behind your back, touch the red probe on the volt meter to the positive lead of capacitor C28 on the logic board (see the photograph on the next page) to see if you have +5V on the logic board.". The **With one hand behind your back** line made me ROFLOL.
Were you ever able to get the short to reappear? Maybe it's in the drive assembly, I'm not sure if you tested that or not.
Regarding checking for voltages, PCs have a standby power rail as well as main power rails. Presumably the iMac is similar. The 5V Steve found is probably this standby source and its presence doesn't mean the main rails work. If you know how the motherboard "talks" to the power supply I would check to see if it is commanding the supply on. If the power supply is commanded on but isn't turning on then you know it's a basic power issue (likely short circuit protection). If the supply is NOT commanded on then then you have bigger issues.
Did you check the hard drive power cable for shorts? Or the hard drive? Does the short still occur with the drive power unplugged from the board? CD drive?
“Open up the butter packet” OMG a MADtv reference lol
Make sure to check any accessories like the CD drive and HDD
Having no idea how iMac logic boards work (never stopped me from making suggestions before), I believe the PPC 750 processor is rated at 3.3V, so there's either going to be a separate 3.3V rail from the PSU, or there's some local regulation on the board somewhere. Always check yo voltage rails!
I know you tried to see if the red wire put out 5 Volts DC to ground but did you try the other of the power rail to see if the yellow lead on the hard drive to the power supply on the logic board to ground put out 12 volts dc Because if you do not have both voltages then there might be a short because computers use 5 volts and 12v they do use other values in some instances but that’s just somewhere to start You could also check to see if you’re getting 5 V out of the keyboard port When you have the power supply connected and 12 V for the remaining components like the cooling fans
8:27 "Open up the butter packet.."🤣😂
That's some old school MadTV! The John Madden Quick Pop Popcorn Popper
🤣😂🤣😂
Oh my god
I threw away a tray-loader iMac that wouldn't boot anymore years ago and I don't remember trying to reseat the processor card 🤦
Hey Ken, man I dont want to sound mean or anything but right now, I'm on the proccess of diagnosing voltajes on a trayload imac g3 that turns on by itself by plugging it in, but no boot not chime, and I've been unable to find any service manual neither any diagram of the board ( same retail board) and now Steve does exactly what I need to do..... but covers what and where is he measuring.. with his HUGE hand god damn it!!!.
Could it be the shield sorting the board? It’s not shorted out of the case…
As for the ADB - it doesn't surprise me. The "Professional" Power Mac G3 (Blue & White) kept the ADB port while moving to USB. (And humorously the visually matching Apple Studio Display 15" LCD, while it changed the video plug to VGA over Apple's DA-15 video port, it _didn't_ have a USB hub in it, it had ADB! It wasn't until the graphte-G4-matching Studio Display that it got a USB hub instead.)
Awesome video! Always cool to see this rare machine, can’t wait for more!
Thank you! 😇
15:10, "Rocket surgeon" nice.
I inherited from my father a Gebruder Resch Vienna Regulator (pendulum) wall clock. Dad had inherited it from his father, but could never get it to work, When it came to me, I disassembled it and saw a number of parts were broken or crudely repaired.
I bought the movement from another Gebruder Resch regulator with similar serial number and replaced:
The chime flirt
The pendulum bob
The right weight pulley
The rack pin
The fan
I was told by an antiques dealer that because I had used period original parts from the same manufacturer, I would be justified in selling it as an original.
The clock is still going strong. It was my first attempt at a clock repair, but it's a hobby of mine now.
this makes me chringe especially if the retail board was a REV B vs a REV A board. there were slight power differences and a rev B in a REVA analog / power will will fry a board.
Maybe Adrian Black could take a shot at this one.
Maybe the ram slots need to be populated before power on will proceed?
My guess is the casing/bracket is touching a contact directly as the short disappeared after removing it.
All this talk about bad caps or whatever, I didn’t quite understand the short issue. Was the resistance actually checked between VCC and ground rather than a continuity check?
The little board appears to only have an inductor on it, so don’t really understand what can go wrong here.
Also, voltage was present on the “shorted” board?
Voltage reference should be 3.3 and 5 volts needed. Swap out the CPU module. Better still, compare these resistances between ground and VCC. Anything greater than 10 megs is usually ok
Use a thermal camera to see if any part is overheating
13:30 - So there was a short between 5V and Ground on the proto board at that point.
13:50 - But the short disappeared once the board was removed from the chassis.
It's generally not so likely that a chunky filter inductor would cause a short like that (vs a filter for higher voltages like mains).
But did you test the hard drive power connector for a short between 5V and Ground, with the connector unplugged from the mobo?
My bet is it's the HDD, CD drive, or some other device external to the logic board that has a short.
As a process of elimination, the filter inductor module can just be unplugged from the mobo, then check again for a short on the 5V rail.
If the short is still present, unplug the HDD power connector, check again, and so on.
oic, later on, with the mobo back in the chassis (and HDD supposedly plugged back in), there was 5V on the board again.
Assuming that's the same 5V rail as on the HDD connector (as sometimes there can be multiple rails for the same voltage), that's quite weird.
It depends on what the resistance reading was on the 5V and Ground pins of the HDD power connector with the board in place.
I don't know how the power routing is done on the iMac, but it looks like ALL of the power rails from the PSU pass through the big filter inductor first, and only then to the mobo.
And then presumably it has some FETs or switching regs on the motherboard that allow power through to the HDD and CD drive connectors via the soft-power option?
If that's the case, then there could *still* be a dead short on the HDD power connector, which is why it won't turn on.
Or, if the PSU works more like an ATX PSU (probably), it will have a 5V Standby supply that's always on.
And one or more PS_ON_N control wires to turn the main part of the PSU on.
That could explain why you were getting 5V on a specific part of the motherboard.
But the short on the HDD power connector (or elsewhere on the mobo) is preventing the main part of the PSU from starting up. It's likely just shutting down due to overcurrent protection.
(which will often cause a hissing or clicking sound from the PSU.)
Since you have a good working unit you can always measure the resistance of each chip pin referencing ground an compare differences. If there's an open or short circuit this will narrow it down. Also invest in a huntron for more in depth troubleshooting
Any idea when the follow-up will be uploaded?
The only time I've seen one of these in person was when I was in elementary school, they had a red one running I think MacOS 9.
I was still a Windows fan at the time and I hated Macs so I didn't even bother to look at it very much or use it.
Hear me out… but could the shield tray be sorting the board? It’s not shorted out of the case so it may be that…
How awesome to be back Steve and Ken!
At 14min you were saying that the short was no longer present with the logic board on the bench. Did you try checking other components in the system? CD drive/HDD etc? And where does that black plug you were testing on go to? Try checking the plug itself while NOT plugged into the logic board. Also try booting the system with that not plugged in (im assuming that is the power down to the HDD/CD)
I realize you may of already tried this and it just didnt make it into the video. But that would be my suggestion
That voltage tester be sounding like a Toyota
First thought see if you can rig some extensions for cabling and boot/power the system out of the case, I saw another comment in the thread that suggested that it might be making contact with some of the shielding when you had it out of there it went away. That would eliminate those gremlins at least. I had a Bondi blue iMac, that my roommates boyfriend drunkenly urinated in and of all the things you think that might have damaged it didn’t, the problem surfaced several weeks later when corrosion on part of the shielding was making contact with the board. (Moral of the story don’t let your idiot boyfriend piss in my iMac or you pay all of rent for 90 days)
Try the CMOS reset button on the board? My buddy had a G3 that wouldn't boot and that fixed it.
Love the new intro, haven’t watched for a while, been busy, but great work
The intro has been the same for a couple years, but thank you! I change the montage clips every so often, but that aside, it's been the tried and true intro I've used for a long time. : )
I would check the power cable that is connecting to the board to see if the power supply is shorting out. When you guys were testing the red and black cables while connected to the board, it was shorted. What happens when you disconnect that 4-pin connector (red, black, black, yellow) and test the continuity to see if you get a short on the connector itself
Any followup for this g3?
Sense after you removed the board did you check the power cable of the drive for an upstream downstream fault?
Maybe all you have to do is to get a new battery and proper ram. I believe those imacs just refuse to start altoghether if the pram battery is drained.
Did I miss where you checked for the short after removing the HDD power? Because I am pretty sure that would be a great test...
That was my exact thought. Doubt the short magically went away on its own after all. Kind of figure it has to either be further down the chain from that connector. That or its a short from a random trace or solder point thats making contact with the chassis. May have been ruled out off screen, but ruling out and finding the definitive origin of that short to ground would be a great test to pursue if they haven't
Try spray the board with air duster upside down and see what chip is getting hot and you should find your short. You can also use a thermal camera. Probably not a chip though, I would check all the caps first.
test those capacitors on the logic board with an in circuit esr tester
Did you Try unplugging the Harddrive Powercable? Maybe the Harddrive is shorting something together. it should at least start up to the qustion mark symbol.
Fantastic content! Those late-night computer diagnoses are some of the best moments in life! Reminds me of when I turned my inspiron 8500 into a dual-boot with a tactical version of Ubuntu 😁😁
Are you plugging the drives back in? Because they could be the problem.
Send it to Louis Rossmann, he'll get you fan spin.
You probably already checked, but I thought I'd ask. Did you try unplugging the hard drive power from the logic board then checking for a short? Short could possibly be in hard drive or pigtail.
Do these not have a CUDA button? I had a later model CRT iMac that wouldn't do anything until I pressed the CUDA button inside.
Good effort! I wish I had a mac84 under my workbench.
The board is shorting to the case isolate the downside of the board or the case replace the hard drive cable or the hard drive
there’s a lot of different types of prototypes Apple made.
Some of these prototypes are really cool to see. (Including that iMac g3)
I really hope you find other types of
Prototypes in the future.
I got one of those, bought as soon as it came on the market. Works perfectly! It's fun to play the old games every now and then. :D
How about using a thermal camera and seeing what is overheating
"Push the button, Frank." I expect nothing less from a man that actually looks like Frank Conniff.
to see the contents of the prototype drive, cant you guys plug in the prototype drive into the retail board?
So the short was found on the hard drive connector while the drive was plugged in, did you test the drive it's self?
Hopefully we can get the whole traffic under the table problem sorted out *eventually*
As far as I know I still have one working condition in the loft.
Guys, you’ve not tried powering it up with the power to the drives disconnected, that’s the first thing I’d try.
I, too, hate under desk traffic!
Can’t wait to find out what’s going on, I have a iMac G3 indigo that I have that was doing the same thing! I could hear electricity but it would never start
That intro give me such fun vibes. I barely started watching and I’m excited to see the kraziness! 😁
would cleaning the board help ?
is there a follow up to this?
You'd need a lab bench power supply. disconnect the power supply board, put 1v 5a into the shorted rail and see what component on the board is heating. Then desolder that component and retry until the short is gone. After that, replace all desoldered components. This can be tricky though if there are power converters on the board, because this method will not help you find a shorted MOSFET
16:40 haha, amp jacks covered to prevent "somebody" to screw up :DDD
him:just says its not gonna work me:really sad
Switch the CD drive from the retail model to the prototype to see if its the drive causing the short due to some internal electrical fault
could you please link the service manual you guys used?
Great intro, can't wait for the rest of the show
did this ever get solved?
Try Checking Tantulums
Then You Can try Dissconect The Drives And Everything That You Can Disconnect because THAT Might Give System The Error To Not Boot
Guys, I'm telling ya, they aren't that hard to fully disassemble. I rebuilt a set of those about 15 yrs ago. No manual either. I have to call y'all out on that. These are soo simple to take apart, just be careful.
Apple hater here but love these things because I love all things technology. Thanks for the information.
"I'm not a rocket surgeon." - Krazy Ken 2021
Just a random suggestion, maybe try the prototype logic board in the retail machine's logic board sled
When you took the board out it made me think that there could be some weird thing like the iMac took a bump or a drop during shipping or something like that in its lifetime and the sled had become just slightly warped enough to touch the bottom of the logic board making a short
Would love to see an update video!
this is simpler then you think
just desolder two diodes next to power plug on Hard Disk Drive
you have burned diode, which goes into dead short when burned
BUFFERING then: steve!
I feel like adrian black could have that thing up and going in less than half an hour.
"I'm not a rocket surgeon" ROTFLMAO!
Push the button, Frank.