iMac G3 high voltage noise

[tony359]

Hi there

I've collected an old iMac G3 for next to nothing and after adding RAM and an HDD it works (lovely machine!)

Only issue, I hear a slight high voltage "click" every now and then and the picture jumps for a split second. I understand it should be the flyback transformer - or the cable come loose.

I would like to have a look to see if it's anything easy - I'll be careful.
However, the weird thing is that it started clicking like once every minute when cold and then basically stopped when hot. Does that tell anything about the cause of the issue?

Thanks!

 

[Alexis Trinquet]

Sounds like something is arcing in the HV section.

If it's a tray loader, it could be a FBT issue (unlikely but...) or that some dust and other grime got underneath the anode cap.

 

[tony359]

Hi - I'm not too familiar with these series but the disc load in a slot, there isn't a tray coming out.
I can indeed clean the cable and the surrounding areas. I've removed the HV cable before on a CRT projector and if I remember correctly the cable is kept in place by a spring on the flyback trasformer itself - that is, you push and twist and the cable comes off?

Thanks for your input!

 

[DeltaMac]

Don't forget to short that HV cable to the chassis before you disconnect from the CRT. A few thousand volts be a "shocking" experience for you

 

[tony359]

Absolutely! And I'll also make sure the system is unplugged for 24 hours before I even do that! Thanks for mentioning!

 

[Alexis Trinquet]

Hi - I'm not too familiar with these series but the disc load in a slot, there isn't a tray coming out.
I can indeed clean the cable and the surrounding areas. I've removed the HV cable before on a CRT projector and if I remember correctly the cable is kept in place by a spring on the flyback trasformer itself - that is, you push and twist and the cable comes off?

Thanks for your input!

On some FBTs you can disconnect the cable from the FBT's shell, but not all of them AFAIK.

The part where it could be arcing would be the "Ultor" or "Anode cap", where the red HV wire connects to the tube, I belive on the slot loaders it's on the bottom of the tube (since SL G3s have the tube mounted upside down, as the anode cap normally is supposed to face upwards).

If cleaning the anode cap area doesn't do any better, then it could be that the arcing is happening in the FBT itself, from memory, I know that some Apple CRTs (those sold with the Power Macintosh G3 "Blue & White" and briefly with the early G4s) would both suffer a similar failure, their FBTs would degrade and begin arcing inside, causing the same "image shrink and tick" effect.

 

[tony359]

Thanks, this is important information. I will keep you posted!

 

[tony359]

Hello,

I just wanted to follow up on this. I disassembled the iMac and cleaned the HV lead, sucker and surrounding areas. Today I had a chance to leave it on for a while and I am happy to report that the HV "clicks" have gone, along with the picture issues.

Thanks a lot for your inputs!!