Guys,


I have probably 200 hrs on re-tubed 8500, new red and blue ( working fine ), rebuilt VDC green.

The green has just developed the dreaded spot kill on shut down. :eek: I have taken the red neck card and installed on green, still got the spot. :mad:

I don't recall hearing the HV crackle on start up, but everything else is working ok with no abnormal diagnostic lites on.

The tube doesn't have a burn yet, so I am looking for other things to check so as to fire it up as minimally as possible.

Anything else to check?
Tube toast?

Jim

Anything else to check?


That problem could also be coming from the VIM. Swap the mini RCA connectors on the VIM (red<>green).

If not the neck board, it's most likely the VIM. And can also be the G2 lead (circuit in HVPS) to the effected neck board.

That problem could also be coming from the VIM. Swap the mini RCA connectors on the VIM (red<>green).

If not the neck board, it's most likely the VIM. And can also be the G2 lead (circuit in HVPS) to the effected neck board.

Thanks Mike.

I swapped RCA's on VIM (red and green) no luck.
I don't seem to have the HV crackle, but diagnostic lites are all normal.

Any way of checking the G2 circuit in the HVPS?

Jim

Hello

It could be the tube, or the G2 is not dropping at power-off like it needs to; try swapping red and green G2 feeds or put a voltmeter on the green neckboard at the tip of R76; it should slam from 550 volts dc to nil very fast.

If it is the tube and the phosphor is not scarring you might as well just use it.

If it's a sharp dot at shutdown, it could be an issue. If it's more like a dim firework explosion in the middle of the screen, then no worries.

You do have HV, or you'd have no picture at all..:)

Ps: re-reading the above, it's most likely a function of the tube, but as Tim says, this is probably due to a shifting cutoff voltage within the tube that will not cause any damage over a period of years.

Hello

It could be the tube, or the G2 is not dropping at power-off like it needs to; try swapping red and green G2 feeds or put a voltmeter on the green neckboard at the tip of R76; it should slam from 550 volts dc to nil very fast.

If it is the tube and the phosphor is not scarring you might as well just use it.

Tim

At the tip of R76 I have 575vdc, at shutdown it slams to less than 1/2v.

Thanks
Jim

If it's a sharp dot at shutdown, it could be an issue. If it's more like a dim firework explosion in the middle of the screen, then no worries.

You do have HV, or you'd have no picture at all..:)

Ps: re-reading the above, it's most likely a function of the tube, but as Tim says, this is probably due to a shifting cutoff voltage within the tube that will not cause any damage over a period of years.


Curt,

It looks about 1 pixel and then has what looks like a negative spike on a scope about 1-2" long.
It doesn't look any brighter than any of the menu screens.

I tried to take some pics with no success.

Thanks
Jim