iMac G3 power on issues

[Ryanteck]

Hi,

I have recently acquired a G3 iMac tangerine edition of which it has the common power up issue however while there's lots of mentions about what is the likely culprit there's no clear "check this part" from what I can tell.

The problem is when I press the power button I get the chime, screen works perfectly but after about 10 seconds it shuts down. Then attempts after are just resulted in a pop noise from the speakers and the CRT power off noise.

Research is indicating the PAV board which is hard to get to. I understand there's high voltages and will take care when repairing it by discharging the crt but most threads stop there.

So far I haven't taken the cover off but the capacitor inside looks very bulgy. However then some other threads I see indicate this could be normal for imacs despite usually being a clear sign of failure?

How do I go diagnosing the faulty part. I have multi meters, decent soldering gear, oscilioscope and such. While one option is to get a working PAV board the hassle of taking it apart I might as well repair it if possible as a replacement has a high chance of developing the same issue compared to for example if it's the capacitor getting a brand new one of decent quality and high lifetime.

 

[AL1630]

First try replacing the PRAM battery. My iMac G3 used to do that a couple years ago and I replaced the battery, and it hasn't done that since (Knock on wood). The PAV board will most likely go at some point, but I haven't heard of someone successfully fixing one yet.

 

[Ryanteck]

First try replacing the PRAM battery. My iMac G3 used to do that a couple years ago and I replaced the battery, and it hasn't done that since (Knock on wood). The PAV board will most likely go at some point, but I haven't heard of someone successfully fixing one yet.

PRAM Battery ordered and we'll see if that fixes it. If that doesn't fix it then I'll have to diagnose some more as I wouldn't have thought a battery could cause this issue but could see it being one of these weird things that could.

As for repairing the PAV Board I suspect it depends on what's wrong. If its the big capacitor on the board causing it then that should be easy to replace. One of the electrical tests I ran measured quite a low insulation between the L+N and Earth Pins.

Update: I removed the battery, the screen turned on the first time and about 30 seconds later it then shut down and attempts to turn it back on just resulted in the CRT de-gauss noise. I have a new battery on order however might wire a couple of AAs or use a 3v3 power source to try.

 

[Ryanteck]

I'm not fully sure about multiple posts in a row rules however this one justified more than an edit.

I actually just have gone and picked up another iMac for free which is a G3 Grey edition (I believe the DV Models?) I might swap the PAV Boards around as to me the Tangerine is more important to get working than the Grey.

However I tried swapping the PRAM Batteries around and that didn't help. Also comparing the capacitors they both look about as bulgy as eachother. I'll wait for the other PRAM Battery to arrive and try that. If it doesn't fix it then it'll likely be the PAV board I need to diagnose.

 

[pl1984]

What you described sounds like a capacitor issue. I wouldn't be surprised if the problem turns out to be a bad capacitor. They go bad with time, even if they're not bulging. But bulging can be a little misleading. I had a Dell which suffered from the failing capacitor issues of the mid 2000's. I inspected them and they weren't bulging but the top of one was just slightly "rounded" (i.e. not perfectly flat). Replaced it and the system ran fine going forward.

Unless a specific model is known to have boot issues with a weak / dead PRAM battery I can say in 99% of the failure to boot cases it is not the problem. Doesn't hurt / cost much to try it but I can't recall reading where replacing it fixed the failure to boot.

As for the multiple posting rules I can't recall if the rules speak to that or not. My opinion is we're here to share information and I see nothing wrong with it.

 

[DearthnVader]

I have a blueberry iMac board for sale, is the PAV board the small power board connect to the main logic board?

 

[Ryanteck]

@DearthnVader the PAV Board is the one which is on the top just under the CRT. I believe the power board that connects to the logic board is called a stepdown board.

Either way I'm not too interested in replacing my PAV Board as if I replace it with another while it might work for now it'll just develop the same fault in the future so ideally want to learn how to repair it.

 

[DearthnVader]

@DearthnVader the PAV Board is the one which is on the top just under the CRT. I believe the power board that connects to the logic board is called a stepdown board.

Either way I'm not too interested in replacing my PAV Board as if I replace it with another while it might work for now it'll just develop the same fault in the future so ideally want to learn how to repair it.

Ok, let me know if you need parts off the PAV board, free to good home, I have one, but it had an issue of not powering on without a CUDA reset, so I think something on that board was going bad. It didn't have an issue staying on indefinitely once the system powered on.

I really don't know anything about the PAV board, but I can remove any part you may think you need and ship it to you, if you're in the US, for the cost of shipping.

 

[Ryanteck]

Ok, let me know if you need parts off the PAV board, free to good home, I have one, but it had an issue of not powering on without a CUDA reset, so I think something on that board was going bad. It didn't have an issue staying on indefinitely once the system powered on.

I really don't know anything about the PAV board, but I can remove any part you may think you need and ship it to you, if you're in the US, for the cost of shipping.

Thanks very much for the offer. However I am in the UK so the shipping would be quite expensive.

For now I have put the entire body from the Graphite machine in the tangerine shell as the tangerine shell was in better condition along with keyboard and mouse.

 

[HeatedCane]

Ok, let me know if you need parts off the PAV board, free to good home, I have one, but it had an issue of not powering on without a CUDA reset, so I think something on that board was going bad. It didn't have an issue staying on indefinitely once the system powered on.

I really don't know anything about the PAV board, but I can remove any part you may think you need and ship it to you, if you're in the US, for the cost of shipping.

Hi, I was wondering do you still have the PAV board? I’d like to buy it off you because I’m having the same issue as the user you were helping out in this post. Let me know thank you!

 

[DearthnVader]

Hi, I was wondering do you still have the PAV board? I’d like to buy it off you because I’m having the same issue as the user you were helping out in this post. Let me know thank you!

I thinkI still have it, but I have no clue what state it's in storage in...

I have a couple of Rev. 1 iMac's with me here in KY, but those parts will likely not do you much good.

 

[HeatedCane]

I thinkI still have it, but I have no clue what state it's in storage in...

I have a couple of Rev. 1 iMac's with me here in KY, but those parts will likely not do you much good.

Got yea well I’d I think I’d still be willing to take the gamble on buying it off you if you do still have it. Lmk.

 

[HeatedCane]

I thinkI still have it, but I have no clue what state it's in storage in...

I have a couple of Rev. 1 iMac's with me here in KY, but those parts will likely not do you much good.

Any luck on finding seeing if you have the PAV board still?