CurtPalme.com Home Theater Forum

draganm · Joined: 08 Mar 2006 Posts: 8990 Location: Colorado

I recently took off the neck-board from my 8500, it had been on the machine for a pretty long time, many years, and it was not easy to remove, like it was "stuck" on the tube pins. I had never seen this before and I have pulled off hundreds of VNB's.

It eventually came off and didn't think anything of it. A couple weeks later I put a different VNB on there and no output from tube. Tried a second vnb , same thing. Swapped leads on VIM , channel is good. Check for G2 voltage, good at 380V.

I have never heard of this but is it possible an output pin was damaged on the tube? I know the pins that are visible are not the actual hi-vacuum pass-thru pins but rather a cover that goes over those, so it seems unlikely that the tube itself is damaged and in-gassed. How fragile is this intermediate piece?

Anyone seen anything like this before?

**Curt Palme** · Posted: Thu Dec 01, 2016 3:30 pm Post subject:

Are you sure a pin didn't pull out of the tube? I've had that happen before a few times. Is the filament on?

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Yes, the pins do pass through the glass seal. If you tweak a pin too hard all the vacuum will leak out.

Generally if this happens, the appearance of the tube face will change due to oxidation of the aluminizing layer.

Inspect the pins and tube neck very carefully. Gently wiggle the pins and if any of the pins moves and you hear glass making grunching noises, you can expect that the tube is wrecked.

Swap two neck boards and give it a test. If the problem stays with the tube, you probably killed the tube.

**Curt Palme** · Posted: Fri Dec 02, 2016 12:15 am Post subject:

I have had pins break off at the glass without breaking the vacuum. THat's what I'm suspecting is happening here.

Tim in Phoenix · Joined: 21 Oct 2006 Posts: 4409 Location: Phoenix

Hey Dragan

I have one new 180DMB blue here, make me an offer. Also have some used in two projectors, I will try to determine condition of those over the weekend

draganm · Joined: 08 Mar 2006 Posts: 8990 Location: Colorado

I don't think any of the pins broke off, none of them even bent AFAik but I'll check again this weekend. Curt have you had any luck soldering in a new pin ?

Tim I saw your tube, I'll definitely be getting that if it's a broken pin/gassy tube on mine

**Curt Palme** · Posted: Fri Dec 02, 2016 5:41 pm Post subject:

No, I never have. Check first if the filament is on. Also, the G2 might be a bit low at 380 volts, maybe swap G2 leads just to check>?

draganm · Joined: 08 Mar 2006 Posts: 8990 Location: Colorado

the filament looks like it's lit, orange glow from neck like normal. I think 380V is ok for an idling machine with no video being displayed but I can swap leads easily enough

I'll take a closer look tonight at the pins

**Curt Palme** · Posted: Fri Dec 02, 2016 6:28 pm Post subject:

Also check the filament voltage. I have had some tubes die almost overnight due to that creeping 6.35 volts going up to over 7. At least you know you have vacuum in the tube, otherwise the filament wouldn't be lit.

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Check your anode connection. (Power OFF!) With no anode voltage you'll have no image at all.

Swap anode leads between two tubes. (At the HV splitter block.) Power off when doing this, and wait for 30 seconds after
turning it off before swapping the leads to allow the HV to bleed off.

Tim in Phoenix · Joined: 21 Oct 2006 Posts: 4409 Location: Phoenix

No

You cannot solder a tube pin. The heat will crack the glass

Tim in Phoenix · Joined: 21 Oct 2006 Posts: 4409 Location: Phoenix

Hey Dragan

Put of a picture of the tube pins

draganm · Joined: 08 Mar 2006 Posts: 8990 Location: Colorado

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Weird, but hey, be glad that it went dark instead of full output!

I always, when working on a Marquee, attach an emergency string to the P14 plug harness, so if I lose G2 control on a tube
I can pull the P14 plug which will shut the tubes down safely after several seconds and avoid the spot burn that is very likely
if you turn off a Marquee via the remote with no G2 control on a tube.

It's pretty much the only way a Marquee can damage a tube.

I did ask for the tube part number. Its specific part number would have told me which pin G2 is on.
For example, P19LCP09RJA vs. P19LCP03RJA are nearly the same tube but the different last number indicates a different G2 pin assignment. (Oddly, in neither case is G2 on pin 9 or 3, so the numbering scheme isn't really very logical.)

What probably happened here is that the beam current limiter on the neck card kicked in and killed the spot before any damage occurred.

draganm · Joined: 08 Mar 2006 Posts: 8990 Location: Colorado

i think the tube has to be a 180DVB, let me see if the number is visible but it's on my ceiling and dark in there

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

That makes sense. DMBs have G2 on pin 2, DVBs and MOST other 8" Panasonic tubes have G2 on pin 6.

It appears that for projection CRTs, pin 6 G2 is the norm, pin 2 is the oddball.