CurtPalme.com Home Theater Forum

chillman · Joined: 09 Apr 2007 Posts: 134 Location: Germany, Bavaria

Hi everybody,
I have my Ampro set up by now, and the picture is great except one thing: The blue tube is always lit up dim all over the phosphor, even without a connected source. This isn't caused by too high G2, G2 setting works normal. Also the lit-up area is not only inside the raster. It is lit up uneven, there's an area which is brighter than the rest. So what could cause this? Broken tube? It's a PT18-205.

papalek · Joined: 08 Mar 2006 Posts: 1536 Location: Longs SC

Swap the neck card with another tube and see if the problem follows it or stays with the blue tube.

**Curt Palme** · Posted: Sat Jan 05, 2008 12:07 am Post subject:

It can also be the sub brightness and sub contrast controls, or some drift in the G2 cutoff. Try swapping neck boards first though.

chillman · Joined: 09 Apr 2007 Posts: 134 Location: Germany, Bavaria

I finally had time to check this and it seems that it's not the neckbord as the problem remains with swapped neckboards. I made a picture of the blue tube, there's actually kind of a second raster which is not affected by G2, and some kind of glow uneven over the phosphor. I made this picture with G2 way down, so you can see the normal raster (displaying a focus test pattern) and also the "second raster". This seems very weird to me, can someone explain this? Is it likely caused by the tube? I also noticed that I have to crank up G2 on the blue tube in order to get it to display low-brightness detail and to be able to get colour balance right.

**AnalogRocks** · Posted: Fri Jan 11, 2008 5:53 pm Post subject:

I've seen this on a Sony 1272 recently too. I'm interested in what causes it.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

What do you have if you pull the video line from the RGB card?

chillman · Joined: 09 Apr 2007 Posts: 134 Location: Germany, Bavaria

It's the same just without the real raster of course.

EDIT: Could it be that there's something glowing in the neck that shouldn't glow and these electrons then are focused on the phosphor? The second raster reacts on geometry adjustments.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

When you swapped the neck boards did you also swap the wire harnesses connecting the the CRT card or use the same ones that were on the tube thats giving you problems?

chillman · Joined: 09 Apr 2007 Posts: 134 Location: Germany, Bavaria

I swapped the neckboard completely, so the wires connected to the neckboard on the blue were the same as before. I will try swapping wires. ( If they are long enough)
EDIT: Didn't change the problem. So it's probably the tube, huh?

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Yes, unfortunately is does look like the tube. It could be a contamination short. Since you have nothing to lose, you could try putting the tube on its face and try tapping the neck with a piece of wood or plastic. Dont use metal. It may dislodge the contaminent. But remember there is risk involved. Even though the tube seems bad you dont want to get injured if you break the neck trying this. Also if you choose to see about having the tube rebuilt then you dont want to break the neck. Also you may want to see if someone has a Sencore to try to remove the short. Some work and some dont. I think the Sencore sheet has the specs to do the MEC tubes. I had one done years ago, but I cant remember the outcome.Your choice now. Good Luck.

chillman · Joined: 09 Apr 2007 Posts: 134 Location: Germany, Bavaria

Alright, thanks for your help, I will remove the tube tomorrow and see if I can fix it or if I can find someone with a Sencore. Fortunately it's not a tube with perfect phosphor so finding a equally good or better tube for cheap should be possible.

tse · Joined: 03 May 2006 Posts: 1014 Location: Sweatbucket, Fl.

The tube does look like it has a secondary emmision problem. It can often be fixed with a Sencore 7000. There are probably other rejuvenators that will work, too.

Scott