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CRT_Ben
Joined: 28 Aug 2006
Posts: 1684
Location: Northern Virginia
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| Posted: Sat Feb 09, 2008 8:09 pm Post subject: Marquee LVPS heater mod questions - yes I've searched! |
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Hey guys,
I'm thinking it's time to do the heater mod because I just measured 6.5VDC at the P14 connector earlier today. So I pulled apart the LVPS and dug around for mod info. I need clarification on some items:
-Why use a 475ohm resistor and a 20ohm pot - why not just a 500ohm pot? ( http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=023-500 )
-If it's necessary to use the 20ohm pot where can you get those? I like PartsExpress but they don't even have anything close to 20ohms.
-My projector was manufactured Sept. 1996 so it seems likely that it had the faulty part. However my LVPS has a blue pot and the soldering definitely looks factory. (see pic) Dragan in this thread seems to think that the bad parts were grey in color with "MEXICO" on top: http://www.curtpalme.com/forum/viewtopic.php?p=28289#28289
Curt, could you write up a procedure that outlines exactly how you do this mod, and what parts you use? I'm aware of this link http://www.curtpalme.com/Marquee_Maintenance2.shtm but to me it seems little incomplete - for example, leaving out the part where you'll probably have to run jumper wires to the new pot and mount it elsewhere in the LVPS: http://www.avsforum.com/avs-vb/showthread.php?p=3279155#post3279155
I'm fairly adept with soldering, etc. but without an electronics degree I'm unsure of acceptable substitutions, if any, and where to get the appropriate parts.
Lastly - is 6.5V too high? If I have to order the parts and wait for them, am I better off not running the PJ until then?
Thanks in advance,
Ben
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garyfritz
Joined: 08 Apr 2006
Posts: 12088
Location: Fort Collins, CO
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| Posted: Sat Feb 09, 2008 8:16 pm Post subject: Re: Marquee LVPS heater mod questions - yes I've searched! |
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| CRT_Ben wrote: | | -Why use a 475ohm resistor and a 20ohm pot - why not just a 500ohm pot? |
I think the problematic part IS something like a 500 ohm pot. Problem is, a 500 ohm pot can go anywhere from 0 to 500. Too-low values cause too-high voltage.
475 + 0-20 can only range between 475 and 495. That way the pot fine-tunes the right value, but even if the pot completely shorts out you're still going to be fairly close.
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CRT_Ben
Joined: 28 Aug 2006
Posts: 1684
Location: Northern Virginia
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| Posted: Sat Feb 09, 2008 8:25 pm Post subject: Re: Marquee LVPS heater mod questions - yes I've searched! |
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| garyfritz wrote: | | CRT_Ben wrote: | | -Why use a 475ohm resistor and a 20ohm pot - why not just a 500ohm pot? |
I think the problematic part IS something like a 500 ohm pot. Problem is, a 500 ohm pot can go anywhere from 0 to 500. Too-low values cause too-high voltage.
475 + 0-20 can only range between 475 and 495. That way the pot fine-tunes the right value, but even if the pot completely shorts out you're still going to be fairly close. |
Ok, that makes good sense - I see now the logic behind using 2 components instead of 1. I also recall that Tim had something up on his website about this mod? But http://www.etechvideo.com/ is dead, at least for now...
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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CRT_Ben
Joined: 28 Aug 2006
Posts: 1684
Location: Northern Virginia
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| Posted: Sat Feb 09, 2008 8:38 pm Post subject: |
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| Nashou66 wrote: | Hello Ben, Here is a pic from the marquee maintanance group purchase thread that shows the resitor change under the board.
http://www.curtpalme.com/forum/download.php?id=3547
Athanasios
You must also cut the trace on top for this i belive. its in the thread i got the pic from . |
I did see that in a different thread - it's a good trick that makes it much easier to use a standard (not SMT) resistor. However it looks like they must have found a 20ohm pot small enough to fit directly on the circuit board?
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Tim in Phoenix
Joined: 21 Oct 2006
Posts: 4409
Location: Phoenix
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| Posted: Sat Feb 09, 2008 9:44 pm Post subject: Re: Marquee LVPS heater mod questions - yes I've searched! |
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| CRT_Ben wrote: | [
.......... I also recall that Tim had something up on his website about this mod? But http://www.etechvideo.com/ is dead, at least for now... |
Guys!
My hosting outfit hit the wall with no warning......
"Dear OnSmart Network Customer, Due to the difficulty in web hosting industry, we decided to close our business in March, 2008. In order to help our customers to transfer out to other web hosting provider. We have open a temporary help desk at http://help.onsmart.net/center/contact to keep track each transfer issue. Sorry for the inconvenience. Jacky OnSmart Network htttp://www.onsmart.net/"
I am currently pondering the move to another host, I will announce when we are running again. Our E-Tech/Papst fan mod includes the filament fix at no extra cost.
.
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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: Sat Feb 09, 2008 10:45 pm Post subject: |
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Sorry, this is a component level repair, I won't be posting details.
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draganm
Joined: 08 Mar 2006
Posts: 8990
Location: Colorado
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| Posted: Sat Feb 09, 2008 11:46 pm Post subject: Re: Marquee LVPS heater mod questions - yes I've searched! |
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| CRT_Ben wrote: | | -My projector was manufactured Sept. 1996 so it seems likely that it had the faulty part. However my LVPS has a blue pot and the soldering definitely looks factory. (see pic) Dragan in this thread seems to think that the bad parts were grey in color with "MEXICO" on top: http://www.curtpalme.com/forum/viewtopic.php?p=28289#28289 |
Well what i've said in the past is if you have the blue pot you should be ok but you unless you've done the mod you should check the P14 voltage 2 or 3 times a year just to be sure. If you have the Mexican pot then you MUST do the mod ASAP. I have seen thoss things drift up towards 7 volts. 
| CRT_Ben wrote: | Lastly - is 6.5V too high? If I have to order the parts and wait for them, am I better off not running the PJ until then?
Thanks in advance,
Ben |
that's borderline, but considering the cost of new tubes do you really want to gamble?
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Joust
Joined: 05 May 2006
Posts: 2429
Location: Almonte, Ontario, Canada
TV/Projector: Marquee 8501LC
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| Posted: Sun Feb 10, 2008 4:36 am Post subject: Re: Marquee LVPS heater mod questions - yes I've searched! |
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| CRT_Ben wrote: |
-Why use a 475ohm resistor and a 20ohm pot - why not just a 500ohm pot? |
You could use one, The smaller the pot the more granular the adjustment is.
You simply have to ensure that your voltage divider is calculated properly.
a word of caution. if you do try something else. disconnect P14 and measure the voltage before you plug it in.
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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: Sun Feb 10, 2008 4:23 pm Post subject: Re: Marquee LVPS heater mod questions - yes I've searched! |
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| draganm wrote: | | If you have the Mexican pot then you MUST do the mod ASAP. |
I'd also suggest you get a new dealer. 8)
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CRT_Ben
Joined: 28 Aug 2006
Posts: 1684
Location: Northern Virginia
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| Posted: Sun Feb 10, 2008 4:57 pm Post subject: |
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OK, in order:
Tim - Sorry to hear that! I hope you get up and running soon.
Curt - Fair enough, I understand.
Dragan - I'll reply to your email in a bit, but is it unwise to tweak the factory pot in the meantime, knowing that I'll be replacing it soon, one way or another?
Joust - Thanks for the info. I think I'll stick with the established design because it's proven, and the fine adjustment sounds much nicer to dial in.
Curt - 
Thanks for all the help, guys!
Ben
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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AnalogRocks
Forum Moderator
Joined: 08 Mar 2006
Posts: 26706
Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
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| Posted: Mon Feb 11, 2008 7:44 am Post subject: Re: Marquee LVPS heater mod questions - yes I've searched! |
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| Curt Palme wrote: | | draganm wrote: | | If you have the Mexican pot then you MUST do the mod ASAP. |
I'd also suggest you get a new dealer. 8) |
Good BC humour. 
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HD done right!
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draganm
Joined: 08 Mar 2006
Posts: 8990
Location: Colorado
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| Posted: Mon Feb 11, 2008 10:18 pm Post subject: |
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| Curt Palme wrote: | | draganm wrote: | | If you have the Mexican pot then you MUST do the mod ASAP. |
I'd also suggest you get a new dealer. 8) |
LOL, I think it's been a least 10 years since I think of that when Someone uses the word Pot. I would say now with wife + kids cooking pot takes first place with trim-pot a close second.
| CRT_Ben wrote: | | is it unwise to tweak the factory pot in the meantime, knowing that I'll be replacing it soon, one way or another?Ben |
go right ahead, it will adjust fine with the Blue trimmer but it might or might not stay there. The Gray one was always very jumpy though, and wouldn't stay put to save your life (or your tubes).
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AnalogRocks
Forum Moderator
Joined: 08 Mar 2006
Posts: 26706
Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
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| Posted: Tue Feb 12, 2008 2:30 am Post subject: |
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| draganm wrote: |
| CRT_Ben wrote: | | is it unwise to tweak the factory pot in the meantime, knowing that I'll be replacing it soon, one way or another?Ben |
go right ahead, it will adjust fine with the Blue trimmer but it might or might not stay there. The Gray one was always very jumpy though, and wouldn't stay put to save your life (or your tubes). |
Would that make it a Mexican Jumping Pot?
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HD done right!
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