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jontag
Joined: 24 May 2010
Posts: 5
Location: Phoenix, Az. USA
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| Posted: Mon May 24, 2010 4:18 am Post subject: Blue tube very dim on marquee 8500 |
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I picked this projector up over a year ago for almost literally pennies($29.99) and have gotten great use out of it.
A couple of weeks back the blue tube didn't come fully on. tried the obvious of switching boards and plugs and have gone as far as physically switching the red and blue tubes. Red tube works hooked up to blue side but no change with blue tube on red side...still very dim(only visible looking directly in). Tube face looks better than i thought it would, a 7 or 8 rating, considering 9800 hrs.
Oh, almost forgot the blue did come fully on a couple of days ago... i had forgotten to hook up a couple of wires in my rush to turn it back on after switching some stuff and got a vertical blue line top to bottom flash for a second, turned it off and hooked up what was forgotten and when it turned back on the blue fired up. Worked for about 2 minutes and went back to very dim again.
_________________
Marquee 8500(working) from Goodwill: $30
VGA to 5BNC RGBHV: $27
9' x 6' homemade screen: $30
Phase Technology speakers salvaged off construction remodel: $0
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JustGreg
Joined: 07 Mar 2006
Posts: 3098
Location: Kenosha, WI
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| Posted: Mon May 24, 2010 5:29 am Post subject: |
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I have the same problem with both blue tubes I have (one in, one for spare). Sometime in the past the filament voltage must have been too high and toasted the filament. Have you checked the voltage at P14 yet? If the red tube worked connected to the blue G2; and you also swapped the NB and cabling I'd say it's had it.
If you aren't too picky and don't mind a 6-ish tube CZ Eddie has some he's selling. Look for his ad in the FS forum for Marquee parts.
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Greg
"Is it ignorance or apathy? Hey, I don't know and I don't care!" --Jimmy Buffett
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jontag
Joined: 24 May 2010
Posts: 5
Location: Phoenix, Az. USA
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| Posted: Mon May 24, 2010 6:48 am Post subject: |
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Kinda figured it may be fried... Only thing that doesnt have me convinced is that it started working again if only for a couple of minutes... picture was as good as it was b4 the outage... not sure.
Thanks for the reply and i"ll start looking for replacement which may have to be down the road a bit... company may be going under so nothing but esentials for now
_________________
Marquee 8500(working) from Goodwill: $30
VGA to 5BNC RGBHV: $27
9' x 6' homemade screen: $30
Phase Technology speakers salvaged off construction remodel: $0
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draganm
Joined: 08 Mar 2006
Posts: 8990
Location: Colorado
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| Posted: Mon May 24, 2010 3:17 pm Post subject: |
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| jontag wrote: | Kinda figured it may be fried... Only thing that doesnt have me convinced is that it started working again if only for a couple of minutes... picture was as good as it was b4 the outage... not sure.
Thanks for the reply and i"ll start looking for replacement which may have to be down the road a bit... company may be going under so nothing but essentials for now |
Replacing the tube will get you up and running but unless you check and fix the filament voltage you will simply burn out more tubes. Look on the front of the machine, if it's a 1995,96,97 model then you can almost bet it will have the bad voltage controler (trim pot) inside the power supply. I have a buddy by Bell road & 43rd Ave. with a used blue tube, I'll see if he still has it.
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Sparky015
Joined: 12 May 2009
Posts: 1185
Location: Cleveland / Akron, OH
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| Posted: Mon May 24, 2010 3:47 pm Post subject: |
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also check the buy/sell forum. there are at least 2 people (myself included) with 9 rated tubes at very good prices. There are used tubes as well.
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~Paul
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Mon May 24, 2010 3:55 pm Post subject: |
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I've never seen a tube go low in output, then normal again, then low again. Makes no sense, but it's not the first time that CRTs don't make sense to me. 
A 100% for sure test: Swap the blue and green tube locations physically. That way EVERYTHING driving the green tube will now drive the blue, and vice versa. If the blue tube stays dim, then it's the tube for sure.
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JustGreg
Joined: 07 Mar 2006
Posts: 3098
Location: Kenosha, WI
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| Posted: Mon May 24, 2010 6:19 pm Post subject: |
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| Curt Palme wrote: | I've never seen a tube go low in output, then normal again, then low again. Makes no sense, but it's not the first time that CRTs don't make sense to me.
A 100% for sure test: Swap the blue and green tube locations physically. That way EVERYTHING driving the green tube will now drive the blue, and vice versa. If the blue tube stays dim, then it's the tube for sure. |
Isn't overdriving a tube the same (if you squint real hard) akin to the way a tube rejuvenator works? eg, super heats 'crap' on the filament, filament/cathode and burns it away? Granted, the results are spurious and not always permanent (especially with FP CRT tubes as opposed to 15" multi rez PC monitors). That's probably why the OP saw his tube 'restored' for a couple minutes.
I've been slowly getting things updated on my 8500 and fired it up yesterday only to have the blue go super bright with G2 and drive set to factory on G&R but higher G2 on blue due to it's low emission condition, to achieve the 'same' ouput as the other tubes. I pulled the board (NB) and suspect there must be a bad new cap, resistor, or opamp. (I'm leaning toward a bad Ohmite at R76 or 81) This post, with those results, sure do get me thinking if it's possible to build a poor mans rejuvenator using a pj's built in HV. 
Radiation emissions would be a huge concern. I'm not worried about blowing the tube up, and although I've had all the kids I ever want; I don't want my face to melt off either.  (some would argue it would be an improvement). I don't want the I Sense circuit to take out the VIM either so it may not work.
Knowing when to realize you're in over your head is critical too! (Kids don't try this at home factor).
Restoring (a tube) is always a last ditch effort to save a tube anyway, so what do I have to lose?
Here's an article by Jestine Yong, EE tech and writer. He's big in the DIY dot com world. If anything this article is informative and written in laymens terms and should in the least provide people with a solid understanding of what's under the hood of a CRT tube.
This article in no way means anyone should try to single out the G2 in a CRT pj tube and attempt to emulate his results for the purpose of saving a (cough cough) 'few' bucks on a new tube; but does beg the question - "I wonder if........."
http://ezinearticles.com/?How-To-Restore-Picture-Tube-Without-using-a-crt-tester,-restorer-or-rejuvenator&id=548647
Obviously the IC would have to be modified to fit the application and methinks a protection circuit to supplement that of the NB is a must also.
As Moe of Three Stooges fame says, "We shall see what we shall see". (Ma-ha, Yeah-ha, Seebeaucoupdofaddymuch?)
_________________
Greg
"Is it ignorance or apathy? Hey, I don't know and I don't care!" --Jimmy Buffett
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jontag
Joined: 24 May 2010
Posts: 5
Location: Phoenix, Az. USA
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| Posted: Tue May 25, 2010 6:54 am Post subject: |
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Thanks for all the replies.
Curt, I physicaly switched red and blue tubes, would putting blue in green spot be diff? Switched red and blue so still had known working green for menu and such, have it in dining room so been using internal signal. Was very frustrating to have it go dim again, I'm pretty sure the neighbors heard me screem. Good thing these things are heavy, pretty sure I started walking tward it with intent to throw.
Draganm: Thanks for the offer, but for now till work gets alot steadier its gonna have to sit. This economy is gonna be the death of me.
Thus begins the planning for the overhaul. This thing is bone stock save for the squeeze mod I did as far as I know. Considering how little I have into it, I shouldn"t complain.
_________________
Marquee 8500(working) from Goodwill: $30
VGA to 5BNC RGBHV: $27
9' x 6' homemade screen: $30
Phase Technology speakers salvaged off construction remodel: $0
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
Posts: 24396
Location: Langley, BC
TV/Projector: All of them!
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| Posted: Tue May 25, 2010 12:46 pm Post subject: |
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OK, wait, so the blue continued to go dim? You weren't clear above...
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JustGreg
Joined: 07 Mar 2006
Posts: 3098
Location: Kenosha, WI
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| Posted: Tue May 25, 2010 7:01 pm Post subject: |
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| Curt Palme wrote: | | OK, wait, so the blue continued to go dim? You weren't clear above... |
If I understood him correctly emissions were low so he did whatever to the nb, then forgot to reconnect 'something', and when he fired it up the tube went super nova, then after reconnecting the whateveritwasheforgot, the tube was 'normal' for a very brief time but then returned to it's pre-tinkeredwith state. Sound about right OP?
_________________
Greg
"Is it ignorance or apathy? Hey, I don't know and I don't care!" --Jimmy Buffett
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jontag
Joined: 24 May 2010
Posts: 5
Location: Phoenix, Az. USA
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| Posted: Thu May 27, 2010 6:38 am Post subject: |
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Thats exactly what happned, though wouldnt call it supernova. Just a verticle bar top to bottom what would be a couple of pixles wide. Wouldnt even say it was overly bright for maybe half a second then faded. worked for maybe 3 min after I hooked up what was missed (honestly dont even remember what wasnt hooked up) then everything went yellowish. It still glows @ the back of the tube same as the green and red, and still shooting a picture but would be like 5 or 10 % brightness at most, not even enough to reach the screen...
EDIT: the blue bar wasnt overly bright. Lasted only half a second
_________________
Marquee 8500(working) from Goodwill: $30
VGA to 5BNC RGBHV: $27
9' x 6' homemade screen: $30
Phase Technology speakers salvaged off construction remodel: $0
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