CurtPalme.com Home Theater Forum

racerxnet · Joined: 20 Jun 2007 Posts: 362 Location: Illinois

I installed new tubes on my 9500 had it up and running. After a week or 2 the Blue tube would start to flicker and then lose output. I swapped out the Green neck card for the Blue and the problem follows. If I shut down the projector and let it sit the tube will function normally for a few minutes and then drop off. Looking at the tube face, it has a ton of noise showing. I can see the overlay of the menu prompt, but the rest of the face is black. I swapped out the HVPS, new neck card, changed signal wires, and reseated all boards. I am stumped and would like to get it running again.

No faults on the LVPS
No faults on the control board
P14 voltage at 6.35 after a good warm up.

MAK

dvh99 · Joined: 25 Dec 2009 Posts: 2158 Location: nederland

so if you swap the blue vnb with the green vnb the problem goes to the green tube?

racerxnet · Joined: 20 Jun 2007 Posts: 362 Location: Illinois

Yep it does. This was after a new neck card was sent to me as well.

dvh99 · Joined: 25 Dec 2009 Posts: 2158 Location: nederland

you disconnected the blue rca cable did you when you swapped neckboards and put the blue rca on the "green" neckboard?
if so it`s the vnb or am i missing something.

if i am missing something you could also swap out the connectors on the cva fgm and hdm to see if this narrows down the problem.

if not its the vim i suppose.

cleaning all connectors on the fgm hdm cva vim and vdm with alcohol and toothbrush might help.

good luck,

dennis

gjaky · Joined: 05 Jun 2010 Posts: 2790 Location: Budapest, Hungary

A little additional information, these are not "normal" boards, but my VNB-DB modification boards (modified VIM, VNB and a daughterboard installed on it).
The boards were sent out tested good, and the blue tube held up for some time, then Mark reported the tube would not fire up anymore. So I sent a fourth neckboard with a new daughterboard (also tested, good), after installation it held up 10 minutes or so as Mark reported, then went dim too. Now it seems the board is working only when it is cold, then drops out. The boards seem to be damaged indeed since when putting on other tube the problem follows the VNB.

barclay66 · Posted: Wed Nov 22, 2017 12:56 pm Post subject:

Hi,

Maybe the tube has some short that puts excessive load on the cathode or G1 amplifiers on the neck board. For a limited amount of time, the amplifiers will work under these conditions but will ultimately fail. A fail analysis on one of the failed neck boards could reveal this (e.g. shorted or open output stage transistors).
The noise pattern on the tube face reminds me of similar effects visible on tubes with shorts between cathode and filament or cathode and G1...

Regards,
barclay66

redfox001 · Joined: 16 Mar 2009 Posts: 2251 Location: The Netherlands

I have a cheap blue tube for sale. Want to get rid of it. Please pm me.

**Curt Palme** · Posted: Wed Nov 22, 2017 3:14 pm Post subject:

While an internal short is possible in any CRT tubes, it's very unlikely. Tap on the neck of the tube to see if you can get the blue tube to act up, but this sounds like an isolated problem with the card. Can you leave a 'good' board on the blue tube, and put a stock original on the green for a couple of weeks to see if you have a problem still?

Is there a chance that the modded board is more prone to static electricity and HV compared to the stock ones? Tim posted long ago about original Marquee boards failing due to normal internal tube arcing, that's what you might have here.

gjaky · Joined: 05 Jun 2010 Posts: 2790 Location: Budapest, Hungary

Of course the „sensitivity” of the modified boards could not be ruled out, but on the other hand at least two other forum member using my mods on regular basis for quite while now, and there was no such complain yet.

dvh99 · Joined: 25 Dec 2009 Posts: 2158 Location: nederland

redfox001 · Joined: 16 Mar 2009 Posts: 2251 Location: The Netherlands

Small thing about static electricity. I used a wallplug without earth for a while and slowly I started hearing small sparks appear during movies. Back to grounded plug and they disappeared again after a while. Still strange that 'after a while' thing Smile

barclay66 · Posted: Fri Nov 24, 2017 8:48 am Post subject:

racerxnet · Joined: 20 Jun 2007 Posts: 362 Location: Illinois

Gabor has been very kind in trying to asses the problem. I thought it was a bit odd that the green neck card swap showed no drop out after running on the Blue tube for several hrs straight. All the ground straps were connected accordingly and also ran grounds to the chassis and wires from the neck cage. I looked at the straps on the Bell as well and looked good. I moved on to the Sony 665es.

MAK