G3 AIO “Molar” issues - Flyback? Caps?

[Durosity]

I was hoping I’d be able to figure this out myself but alas lack of experience and information available has stumped me.

I’ve acquired an AIO G3 here in the UK which is in fairly good physical condition. There’s no battery bomb issues or rust, and the logic board works 100% as I’ve hooked it up to an external display and disconnect the internal video connections from the personality card. However when the internal connections are in place it does the following:

No chime

No LED on front

Fan does start

External monitor does get a signal but it seems to be at a blank command prompt (Open Firmware?)
PSU card clicks a relay when it tries to turn on the screen but then there’s a hissing sound that sounds like it’s from the PSU side

Analog board tries to do something and starts to make a buzzing/hissing sound but no video appears, and then cuts and starts the process again. Some components get very hot and then it shuts off.

I’m really not sure what is causing this and its behaviour seems to be a bit different to what I’ve seen elsewhere. Caps? Flyback? Both?

I see there is a few sources for the Flyback, including this one:

HVT / LOPT 6174Z-1009A for Apple Powermac G3

technotronic-dimensions.3dcartstores.com

Now they seem to indicate the output transistor needs replacing too, and lists two different parts (Sanyo or Fairchild) but I’ve looked all over the boards and I can’t see where this component currently is. Anyone able to point it out to me?

 

[Daniël]

That does sound like the flyback's on the fritz. iMac G3 Trayloaders can exhibit similar symptoms when theirs goes out, and I do believe LG manufactured the CRTs for the AIO as they did for the Trayloaders. Meaning, both got crap quality flyback transformers. If you're going to deal with replacing the flyback, I would suggest going the full mile by doing the caps as well.

 

[Torbar]

Also while you have it open, on the power supply board there's a 20ish pin connector that's goes to a cable for power for the motherboard(very similar to an ATX power cable)

Reflow that connector, because those joints tend to crack as well and cause issues.

 

[Durosity]

Thanks for the replies. Any thoughts on the output transistor? I can’t find any information about it beyond the linked page, so I’m not even sure if it’s actually applicable to the AIO.

 

[Durosity]

Alas I’m not having much luck with getting this working. One of the resistors on the analogue board gets super hot (R726), but I’ve not been able to work out why. I disconnected it and that then burned out R788 but replacing that didn’t help either. I’ve replaced the flyback, the C5404 transistor that’s known to fail, recapped most of the power and analogue board (I tested each cap and replaced all but the ones that tested 100% which was like 85% of the board. Unfortunately that’s about as far as my current knowledge takes me and any requests for assistance elsewhere has been unfruitful.

Anyone have any ideas of next steps?

 

[joshc]

The analog/CRT bits for the Molar Mac were done by LG, same as for the AIOs that preceded the Molar Mac.

I actually don't know if the analog board is unique to the Molar Mac or not, perhaps it is very similar or the same as the one used in the 5x00 machines?

Sorry, I know that doesn't answer your specific query, but just wondering if its really unique parts in that one or not. If not, swapping the analog board from another AIO into the Molar Mac would be an easy way of getting it going.

 

[Durosity]

Alas the 5x00 boards are different, but still manufactured by LG, and the CRT itself is the same. The problem is at the moment I don’t even know for sure that it is the analogue board.. it could be the neck board.. or the power supply.. or heck even a damaged cable! Unfortunately trying to get ahold of other parts I can swap it out with is near on impossible this side of the pond, and certainly not cheap to import (the Mac itself only cost me £75 in shipping fees plus the new flyback but as I’m still not working money is too tight to mention right now!) so I’m *hoping* I can find someone with CRT knowledge that will be able to help.

Fingers crossed

 

[LightBulbFun]

I sadly dont have anything helpful to add regarding the diagnosis other then it might be worth going over the PCB's and checking for cracks in the PCB's themselves, often when items like this get shipped because they are so heavy and have heavy components mounted on said PCB's, the shocks encountered in shipping can actually crack the PCB itself, cutting traces and all that sort of thing

but I just wanted to say its really awesome to hear that you do have a G3 Molar mac here in the UK! I have always wanted to import one myself, but I have never been able to quite figure out how the best way of doing it is I would love to know how ya managed to get such a bulky and heavy item shipped for only £75!

the Mac itself only cost me £75 in shipping fee

i have often thought of doing it by sea-freight, but again im not sure how that all works,

I am also interested in this "bulky heavy item shipping for cheap" thing for my lightbulb hobby side of things as well, as theres a very large Streetlight I really want to import from the US as well (tho I still have to actually find one in the first place!)

 

[Durosity]

but I just wanted to say its really awesome to hear that you do have a G3 Molar mac here in the UK! I have always wanted to import one myself, but I have never been able to quite figure out how the best way of doing it is I would love to know how ya managed to get such a bulky and heavy item shipped for only £75!
i have often thought of doing it by sea-freight, but again im not sure how that all works,

Ah now I just went over my previous posts and realised I didn’t actually say how I got it! I did write a post about this a while ago, but I’m guessing I never actually pressed the post button!

So I didn’t actually import this, I just imported the replacement plastics (hence why it was £75) as the ones this one has were shattered and partially missing. This one I actually found about 10 miles down the road from me when I was buying some VESA mount arms for a monitor. I was just walking out and saw it out the corner of my eye in a pile of junk! It was a moment of sheer confusion. The vesa guy had no idea what it was or where it had came from.. it was about to go in a skip!

So.. I rescued it! It’s clearly had a rough life.. the plastic casing was utterly destroyed. I was lucky enough to be able to convince someone on eBay to sell me the casing from a broken one they had (in hindsight I wish I’d got them to send me the power and analogue boards too). The metal frame to this one is damaged too but I was able to bend it back into place.

I’m hoping I can get it working. I’m still no further forwards, BUT I did find at least one cap I didn’t install correctly when I replaced them, and found one more that was out of spec, so I’ve actually taken off all the caps and I’m gonna put them all back on being super careful to make sure they’re correctly positioned. Fingers crossed!

That said, I have imported other things before. The best being an LC 520 (again rare in Europe as they didn’t really sell them here as best I’m aware) and also black 5500 (which oddly enough came with a UK keyboard). The 520s front bezel shattered in transit, which I was expecting, but other than that was perfectly working and a replacement bezel sorted it out! The 5500 came without a single problem.. which was odd as I had a 5500 shipped from London not long before and it was utterly decimated!

So yeah.. I’m chuffed to have a few rare Macs! If you’re ever in the Newcastle upon Tyne area you’re more than welcome to come have a look at them!

 

[croissantking]

This one I actually found about 10 miles down the road from me

Ah, it was already in the country. There can't be more than half a dozen here, I guess?

 

[Durosity]

I’ve only ever seen one for sale in the UK, back during the pandemic, and I seem to recall it going for an insane amount. But who knows.. maybe there’s more sitting in back rooms waiting to be rediscovered!

Unfortunately I’ve reached the end of what I can do with this now. I’ve replaced every single cap with brand new ones and still the same issue. All the voltages seem to be good. I’ve even replaced the CRT in case it was naffed. Unfortunately whatever is wrong with it is beyond technical abilities to diagnose, and I’ve not been able to get any help from any tv or monitor repair groups that I’ve been able to find. I’m just gonna re-assemble it for now and stick it in the storage rack, hopefully one day I’ll be able to revisit it!

 

[croissantking]

Unfortunately I’ve reached the end of what I can do with this now. I’ve replaced every single cap with brand new ones and still the same issue. All the voltages seem to be good. I’ve even replaced the CRT in case it was naffed. Unfortunately whatever is wrong with it is beyond technical abilities to diagnose, and I’ve not been able to get any help from any tv or monitor repair groups that I’ve been able to find. I’m just gonna re-assemble it for now and stick it in the storage rack, hopefully one day I’ll be able to revisit it!

Did you say you weren’t sure if it was the analog board or the PSU that was the problem? It would surely not be too difficult to rig up an ATX supply to confirm the analog board is what needs service.

From there, I would start to check other components such as diodes and resistors and confirm that all are working to spec. This could obviously take a while… the other option I see would be to look to other forum members in the US who could help you out with a spare analog board.

 

[Durosity]

So the power supply on these also powers the analog board (like the Performa 5x00 series). If I disconnect the analogue board completely then the system will boot, so the ATX side of the power supply works fine, it’s either an issue with it powering the analogue board, or the analogue board has an issue. The power lines from the power supply to the analogue board do hit the voltages expected as per the silkscreen markings without load, and it does with the board connected too, except it then keeps dropping down.. but I don’t know if that’s because it’s shorting and causing it to drop.. or if that would be expected in that circumstance.

As for the diodes and such, yeah that was a thought, but tbh my knowledge of that side of things is awful. I’ve been trying to learn about it but at present I can’t get my ADHD meds so focusing is.. difficult. Ironically not something I ever noticed I had problems with pre diagnosis and medication.. but now I’ve had the meds trying to learn anything new is impossible.

As for other users, alas I’ve not had any luck finding anyone who has any knowledge of them on that side. I’d love to be able to buy a replacement known working but moneys too tight to mention as Mick Hucknall once said

 

[croissantking]

Did you say the PSU was recapped?

What is it actually doing when the analog board is connected? Which rails are dropping down?

As for the diodes and such, yeah that was a thought, but tbh my knowledge of that side of things is awful. I’ve been trying to learn about it but at present I can’t get my ADHD meds so focusing is.. difficult. Ironically not something I ever noticed I had problems with pre diagnosis and medication.. but now I’ve had the meds trying to learn anything new is impossible.

My knowledge isn’t advanced either but perhaps you could start by using a multimeter in continuity mode to check any ceramic caps and diodes for shorts. Place the leads across each component in turn and see if it beeps (it shouldn’t).

Maybe map out the analog board beforehand by taking a photo, printing it out and marking off each component you’ve tested as you go along.

 

[joshc]

Do these run just as hot as other AIOs made by Apple? Is it worth reflowing all the joints as another starting point if not done already?
Sorry, my knowledge is limited here too, but its always good to rule out the easy things.

 

[croissantking]

Do these run just as hot as other AIOs made by Apple? Is it worth reflowing all the joints as another starting point if not done already?
Sorry, my knowledge is limited here too, but its always good to rule out the easy things.

Exactly, there are many different things you can try as well as many different approaches to troubleshooting.

Perseverance is the main key.

 

[joshc]

Basically, analog boards and power supplies are hell to work on (at least from my perspective, as a bit of an electronics noob), unless you are really accustomed to how they actually work and have some of that core electrical engineering skillset - I attended electronics class at school but I wouldn't say I remember a lot of it, and I've never properly sat down and spent the time to learn the skill in a serious way.

There is a difference between swapping components, poking at things with a multimeter, and trying stuff like reflowing solder joints, to actually understanding a schematic properly and having that electrical engineering mindset of how to troubleshoot a complex circuit properly.

Also, having no schematic available doesn't help matters at all...

It doesn't help that analog boards and PSUs contain lots of high voltage things as well, things can get spicy...I know everyone knows this, but please stay safe when doing the poking.

 

[Daniël]

Do these run just as hot as other AIOs made by Apple? Is it worth reflowing all the joints as another starting point if not done already?
Sorry, my knowledge is limited here too, but its always good to rule out the easy things.

They probably do run a bit toasty.
From what I've been reading, that's also why the flybacks fail, apparently the lower quality LG made flybacks when overheating, will cook the lacquer off the windings, which then causes the internal arcing which presents itself as unpleasant "zapping", which causes the image to distort as it zaps.

If the internal shorts are bad enough, that can cause the situation to become worse, to the point that the machine won't power on at all, shutting off the second the flyback receives power and immediately shorts itself out.
That's the case for iMac G3s, but also the Molar Mac, which has a strongly related CRT chassis from what I understand.

 

[croissantking]

One of the resistors on the analogue board gets super hot (R726), but I’ve not been able to work out why. I disconnected it and that then burned out R788 but replacing that didn’t help either.

This is your best clue and I suspect there is a problem component in this area. This is where I would start from, maybe seeing what other stuff is connected to R726.

I’ve replaced the flyback, the C5404 transistor that’s known to fail

Did you use a known good flyback?

 

[Daniël]

Ah, I missed that the flyback has since been replaced, disregard my previous comment.
That does make this a more difficult to solve issue, I fear.