iMac G3 DV SE 400: Bad CRT but VGA out works

[XBHS1997]

Hi guys,

I was given a Graphite DV SE 400 Mhz with video issues. And indeed: After several PRAM resets and a PMU reset and a new PRAM battery (which all changed nothing): bad colours, for example the icons + icon names on the desktop have a "pinkish tail" to the right. Sometimes, it partly seemed ok though. I think that when rebooting it will sometimes stay grey, no image at all. After putting it to sleep mode and waking it up, the (bad) image shows again, but darker. When doing this again, it becomes so dark that it's unreadable. HOWEVER when connected to a external display by VGA, the image on the display is faultless. Maybe the right corner isn't as round as the left one but I didn't try to change any settings about this, and the colors are perfect.

My question: Can the PAV board be faulty even if external video works fine?

The thing is that I also have a Graphite 500 with bad CD-drive and badly scratched case, but working. If I somehow manage to find a good Graphite "flip foot" (it's broken on both of them), I could make a good one out of those 2...

And I also have a Snow 600 which makes a buzzing sound when pressing the power button, and then, nothing.

I don't want to kill a repairable unit, and would like to save the Snow. Make 1 good Graphite or kill the 400 for spares? I have others with some broken plastic parts... But I've also been told that a complete case swap (as planned for these 2 Graphite) would be easier and most of all less dangerous than changing parts like the PAV board.

Before I go further I'd like to have an opinion about my last find's problems.

Thanks

Nicolas

edit: Last pic is when connected to the TV by VGA out.

 

[Macdrone]

They all seem to be having the start or end of the same failures.  The power board/analog boards with bad caps will do just what you are experiencing.  Just pull it apart and a recap would bring them all back most likely.  

 

[XBHS1997]

Yes, I think so too.

Has anybody already recapped an iMac G3 PAV board??

 

[XBHS1997]

Nobody?

 

[didius]

Yes, I think so too.

Has anybody already recapped an iMac G3 PAV board??

I have done it, see

https://68kmla.org/forums/index.php?/topic/20661-imac-g3-dv-se-recapping/

A lot of work though.

 

[goncalo]

I have a Rev A iMac that once started to get these colour aberrations like it was burnt out.

This started when I changed the resolution to 1024 by 768.

But by reverting to a lower resolution it magically returned to being a bright and crisp CRT.

 

[techknight]

The CRT is shot. 

That bleeding is caused by a very weak CRT. IF you had a CRT tester like a Sencore CR-70 with the correct adapters, you would find the guns near the red zone. 

Blooming/washed out, with color bleeding is definitely the sign of a weak CRT. You will need to change the CRT. As the gun emissions fade, it takes less voltage to reach the saturation point of the CRT. thats where the blooming and bleeding comes from. The corner focus will be blurred compared to the center of the tube. 

You can get it to clear up again by turning the screen voltage down, but it will get to the point where its so dim, you cant see it without the blooming and bleeding. 

Drifting voltages on the grids will do the same thing and mimic this issue, but if that machine spent most of its life turned on with the CRT burning all hours of the day, its likely weak.