iMac G3 Runs 1 hour, freezes, reset button results in black screen

Hey Graham and Welcome to Apple Discussions,
Wow, 9.2.2? What applications are you running there? I actually still use 9 for SMIs of applications that will only use 9 in iMacs that are donated to schools.
A local paper just retired theirs this last year.
Do you see any video anomalies when this failure occurs?
The classic failure pattern for these iMac G3s is that the PAV board goes out. The PAV is the power supply for the monitor section but the logic board derives power from it via the down converter. That's a small board on the side of the logic board and I've heard of them going bad but never seen it.
I have 3 logic boards w/ down converters in my spares stock. I have a lot of 350s which were donated from a school and I swap faster logic boards into them from non working FireWire models. Ultimately tho' I wind up w/ a lot of units w/ nonworking PAVs. You're welcome to any parts that I have but I don't think that's your problem.
The good news is that there are a lot of G3s out there and also G4s. We have 2 G4s (4 altogether)17" 800s here. 1 my wife uses and the other I run pdfs and DVDs on in my tech shop.
Richard

Message was edited by: spudnuty

Hey Graham,

And thanks for the offer of spare part's, but I just don't think it's worth it,.. shipping parts to the UK would cost,

Yah I didn't notice that you were in the UK.

lots of G3's about selling very cheap indeed

Yes for as cheaply as $20 around here for the 350.
I know what you mean. Here's a quote from my blurb:
"The iMac in particular is very desirable in these situations:
a) It has a small footprint and is self contained.
b) I have a large amount of educational software that I load them up with.
c) The kids love them. I have seen iMacs get hugged. I never see that with any other computer."
I actually had someone donate an old iMac to me. I had it in the back of my van and I actually had to walk away for a bit while he said goodbye to it!
You could actually have a temperature problem that might have to do w/ the CPU heat sink. I know there were temperature monitoring apps for OS 9 but I don't remember what they were called. If that turns out to be the problem you'll have to take the iMac apart. Email me for instructions if you want to take that on.
Richard

Graham,

..Tricia Helfer desktop ...

Mmmmmm OK I'm Googling...OMG!

.. it said CPU Temp was 2ºC, and as I type it's reading 6ºC (Room Temp is 20ºC) whereas on the new iMac it reads 30ºC

Yah that doesn't look right.

hamster cage for my daughter.

Definitely a thought!

I'd love to have a look inside her, but I recall hearing that these crt's have lethal charges in them for quite a while, & I just don't do dangerous, especially when I can't see it !

Well if you go into the iMac you'd only be going into the bottom - logic board. and dangerous voltages don't exist down there.

As a last ditch attempt, I'm wondering if I should install OSX on it

You must make sure the firmware is upgraded to 4.1.9 and that has to be done in OS 9.
http://support.apple.com/kb/HT1395?viewlocale=en_US

..& use the Temperature software in the OS, maybe that would work better than Gauge Pro in this iMac or maybe that's a waste of time?

That can be a possibility. If it was the CPU temp that's causing this the entire logic board would have to have come loose or perhaps the conductive paste has dried out/failed, unlikely.
So upshot. In my experience the part that fails in these G3 iMacs is the PAV (The board you see when you look down from the top it's under the CRT and drives the monitor section. The logic board derives power from the PAV via down converter).
The shutting down is a classic symptom and the most irritating.
Others: No start - power light blinks or turns amber, video gets wonky - color shifts or size variations, sparks arcing sound, native screen is dark but external monitor works fine (not on option on your 350, no external spigot). This is why I've got 7 or so iMac G3s in my basement. Mostly 350s since I was given around 20 of them and I repaired and donated most into the inner city. The ones left have PAV problems.
Wacky upgrade options:
You could buy a Snow or Graphite 700 (cheap) and clap the exterior pieces onto it from your 350.
You could gut the Blueberry and put an Intel Mac Mini in there w/ a 15" LCD (cheap) and have a totally updated machine, lighter too.

Richard

Message was edited by: spudnuty