CurtPalme.com Home Theater Forum

[Rattanee]

So I'm slowly building my NEC empire, and my latest patient was a PJ I was given by forum member tschaeikaei (Thanks again!) for parts. I managed to salvage the main reason I went through the trouble of having the PJ brought to me across half the EU, that being the point board Anyways, I will want to use the frame of the PJ, so I would like to rule out what may be wrong with the PJ.

I was told that there was something wrong with the neckboards. Well... burnt resistors on the green and red neckboards, and on the green and red outputs of the Video Out PWB. Removing the neckboards, I measured, and found a Heater-Cathode short on both red and green tubes. Once I hooked up my rejuvenator to the tubes, I found no heater glow... so I actually measured between the two heater pins too, and sure enough, all three tubes have open heater circuits... Shame too because the tubes had better phosphor then the tubes in the PG+ I put the point board into...

What would cause such a catastrophic tube failure? Could one tube shorting have caused feedback to the heater circuit and fried the other tubes too, or is it more likely a LVPS fault that put over-voltage out onto the heater circuit? I'd like to figure this out before I do further testing, as I'd prefer not to fry any of my working tubes... also, if anyone has 8508 tubes for a reasonable price, do let me know

Cheers

[Curt Palme]

I've had that once only with a VDC tube. Exactly the same thing. HK short. I then tried zapping the tube, and that killed the filament. I hvae never had a set do it, but that doesn't mean it can't happen. Generally, the filament is completely isolated from the rest of the set, in case of arcing, things don't fire down the chain of circuits in a projector. (or TV).

I have a TON of 8508 tubes, some new with the plastic still over the tube face. Email me NOW, as I was going to toss them due to no interest. I think I can come up with at least 2 sets of NOS tubes.

What I'd do with the set is install one red tube by itself, to see if there's issues. Run that for 100 hours, then put the G and B in. The set will run fine with only one tube installed, but all the yokes, etc need to be connected for the G and B.

[Curt Palme]

I've had that once only with a VDC tube. Exactly the same thing. HK short. I then tried zapping the tube, and that killed the filament. I hvae never had a set do it, but that doesn't mean it can't happen. Generally, the filament is completely isolated from the rest of the set, in case of arcing, things don't fire down the chain of circuits in a projector. (or TV).

I have a TON of 8508 tubes, some new with the plastic still over the tube face. Email me NOW, as I was going to toss them due to no interest. I think I can come up with at least 2 sets of NOS tubes.

What I'd do with the set is install one red tube by itself, to see if there's issues. Run that for 100 hours, then put the G and B in. The set will run fine with only one tube installed, but all the yokes, etc need to be connected for the G and B.

[Rattanee]

I only hooked a single tube up to the rejuvenator, and didn't even try zapping it as I saw no heater glow. I am pretty certain that all three were burnt up by the PJ, and I guess it's also possible that the fault was a high heater voltage from the LVPS that burned out all three filaments, two of which shorted and caused the burnt resistors...

What do I do with the HV leads? Just not plug them in? Will the splitter not arc out if there's nothing plugged into some of it's ports ?

Is it possible to fire it up without tubes? I'd like to check the tube voltages before installing any tubes... also if I do, I have a green with pretty much useless phosphor... so that'll work.

Email sent!

[gjaky]

The set can run without tubes, even with nothing plugged into the splitter, no arcing is expected. But as Curt said all coils for all tubes should be plugged in.