CurtPalme.com Home Theater Forum

[Tim in Phoenix]

Hello

Possible neckboard or VIM issue. At power-off the cathode should slam to black and G2 should drop quickly. You might put a voltmeter on neckboard R76 and see if G2 cuts off quickly. Another possibility is the tube itself

[draganm]

[Nashou66]

I noticed this some times happened on one of my Longbows. After a few times of it happening i never noticed any spot burn so I forgot about it. It might have went away on its own IIRC. How many hours on the tubes?

Nashou

[jbmeyer13]

Does it look something like this when powering down?

https://www.youtube.com/watch?v=fz31tMrXW7g

[tschaeikaei]

So i did it again. It's here: http://youtu.be/sFlrfBbATqg
I use the pic mute (standby) button at 0:42.
Notice the strange deflecting at powering up.
The tubes have about 1500h and the green is a P43.
I took the VIM out some days ago, maybe i have to reseat it?
The dot isn't that bright, not brighter than it appears on the video.
So i believe if everything stays as it is, there is no risk of a spot burn, is it?
I i want to have it gone.

Regards, Julian

[tschaeikaei]

I took the green VNB out and after some resoldering i noticed there are burnt (brown) traces in the area around R10 and R11.
Could the fail lay around here? The two resistors measure 10Ohms like they should.

Regards, Julian

[draganm]

replace that VNB, they're cheap and plentiful and it's nor worth risking a tube.

[tschaeikaei]

Do we know it is the VNB? I am going to change the green and red VNBs and if the failure is depending on the green VNB, i will try to find the fault.
If i don't find it, i will replace it. But... this whole CRT thing is not only to watch movies, but to learn about electronics (for me).

Update: Changed the green with the red VNB, the spot appears on the green tube as it did before.
I would tip on some kind of deflection error. Watching the video, you will notice a strange behavior of the green at powering up between 0:07 and 0:15.
The other tubes don't do that, only the green. You know that those two stripes appearing at 0:16 are normal picture.
It's only stripes because my camera scans with 50Hz while the projector does 60Hz.

Regards, Julian

[jbmeyer13]

[tschaeikaei]

Update: Swapped VNBs, VIM, HDM, CLM. nothing helped to make the problem go away.
But, there is something else that appeared after swapping the green and red VNB.
The green tube is way darker than it shuold be. I reinstalled the green tubes lens
and had to crank G2 up by 10 points to 72 to see the menu on the screen.
It is brighter now, but loosed all contrast. The picture looks like completely washed out on green.
The other two colors are as they should be.
I swapped the VNBs back, the green VNB back on the green tube, same with the red.
The problem stays the same. Strange looking green at powering up, washed out dark picture
and the bright dot at power down.
All the other boards were swapped back. Everything again where i started.
Is there something i can do (preferably measure at the tube pins)
before i dismount the green tube from the other projector and mount it into the projector currently working with?
I don't think that i killed the tube, because nothing spectacular happend.
Every time swapping a board, i powered the projector off with the remote and disconnected the power input cable.
Any idea?

Regards, Julian

[jbmeyer13]

[tschaeikaei]

Is there a possibility to measure the tube in any way?
Do you have a pinout of those 180DMB22?
It should be possible to detect a gatter short with an ohmmeter, right?
I agree that it would be best to swap tubes to see if it is the tube, but thats more work than changing
boards. Could i try with mounting the red neckboard on the green tube and connecting all the inputs
that normaly go to the red VNB to the green one?
I heard that the red phosphor is kind of more efficent than the green or blue, so does it get lower voltages or current?

I will dismount the contrast correction module and be back in some minutes.

Thanks, Julian

[Tim in Phoenix]

Hello

No harm in swapping neckboards. All the signals on the 14 pin cable are identical to all three tubes but you could swap blue G2 and video mini coax to green.

[tschaeikaei]

I did dismount the color correction module -->no difference.
Measured all DC voltages on the blue and green neckboard everything as it is written on the PCB.
And everything the same as you write, Tim.
Brightness goes to -2,3V at 100%.
Measured the blue and green G2 input (not at the tube pin, but at the VNB input.
Something above 600V when brightness is cranked all the way up to 100%.
What what i don't see (looking into the green lens) is that the tube gets brighter when i crank brightness.
Contrast on the remote does make a difference, G2 on the color calibration menu too.
But the brightness button does not have an effect on the green tube.

Anything else that can be measured?
Maybe i swap the green and the blue VNB..

Regards, Julian

[tschaeikaei]

So, the green tube works. I got full brightness again playing with the neckboard, input cables and signals.
The strange powering up and bright dot at powering down stays, but i got a good picture on green.


Update:
Ok, i definitely had a problem with the green VIM. The input capacitor at the 85V rail had a short, or better to say an internal flash-over at higher voltages. No chance to measure it with an ohmmeter or capacity meter.
Changing the capacitor cured the problem with the washed out picture.
I think i know now, where the burned traces come from.
I have a perfectly normal picture again now, but still strange deflection at powering up and the bright dot at powering down.
Regards, Julian

[jbmeyer13]

When you swapped over the G2 and RCA mini connector from blue to green the problem remained, therefore it sounds like the issue is isolated to the green tube itself.

[tschaeikaei]

One problem is solved, so back to the first one.
Yes, jbmeyer. The green is the only tube that did the bright dot and the deflection behavior at power up.
I can't believe it should be the tube itself, nor the deflection coils or any other coil that sits on it.
I would not have a perfectly aligned, even focussed and converged picture otherwise, would i?
I would tip on one of the deflection boards for the powering up behavior.
Will try again later to fix it.
I have to confess, that i didn't watch the powering up and down behavior all the time while i had that dull and dark picture on the green.
That scared me too much about the tube.
Remember it's a P43 green, and i don't want to search months on ebay and pay a price that could me more than
the 2 projectors cost me.
So, i am happy now.

[tschaeikaei]

I swapped all the green with the blue marked connectors on the convergence, vertical and stigmator board.
No change. I'm running out of ideas now. Anyone?

[jbmeyer13]

[tschaeikaei]