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Discussion Starter · #1 ·
I have always suspected that varying or low A/C voltage has something to do with the G90's that crack the tubes as the few I know of seemed to have some sort of possible A/C voltage variation possibility when the tube cracked. This being bad weather leading to brownouts, poor wiring, etc.

I do believe this has now been confirmed.

I have a customer who had a tube crack years ago and when I replaced it I asked him to put a UPS on the AC input as I had suspicions back then that this might be the cause.

A few years go by and the G90 is operating perfectly, then one day I get a call that the PJ is down. Sure enough the G tube is cracked. Customer tells me that one day he tried to turn on the G90 and there was no AC power coming in. He checked the UPS and saw that it wasn't working so he took it out for warranty repair and plugged the G90 directly into the AC. And you guessed it, a few days go by and the tube cracks.

Back when this all started and I recommended that he install a UPS, I asked him about the AC leading to the PJ and he said it was supposed to be a dedicated line. I quized him again this time and he agreed to get an electrician in to check it out. The electrician found that not only wasn't it dedicated but that it was running all his lights and all his equipment (and he has quite a bit) from the one circuit and that the AC voltage was very low and varied as things were turned on. At this point he also looked at the UPS and found that it was performing perfectly and that there was nothing wrong with it (I suspect that the voltage may have been so low so long that the batteries went dead?? when he thought UPS was bad and removed it from the circuit).

From this I am going to conclude what I have suspected for a long time and that is that a low AC voltage WILL cause the G90 to crack a tube. My advise is to put a UPS on the G90's circuit that is large enough to handle the power requirements.


Terry
 

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good info Terry, and more importantly good to hear from you here on AVS. I suspect that AC power problems cause a number of mysterious problems on many CRT's and also AV components in general. A buddy of mine just paid and electrician in Phoenix to run a dedicated line, hang 2 wall sconces, and surround speakers for $400. Money well spent to protect Thousands of dollars
 

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I'll be odd man out here. I completely respect Terry, but I don't follow the logic, although his experience would dictate merit behind what he says.


Here's my counter:


-The G90s (and 70s) have an auto switching supply that ranges from 100 to 240 volts. They are auto regulating, and are designed to compensate for fluctuating voltages. While I've had a couple of SMPS failures in the G90s so far, I have not traced them back specifically to power surges or brownouts.


-While I have not tried it, I suspect that a low voltage condition to the projector will either shut it down completely, or will result in the HV lowering as well.


-I've had tubes shatter in almost all makes and models of sets, including Ampro, Barco and I've seen one Marquee do it too. With the exception of the old analog Barcos that used to eat tubes, I don't see a set design flaw in any of these sets that would cause repetitive cracks in tubes.


Now, am I going to go as far as saying Terry's info is wrong? Heck no!
I agree with Draganm, a UPS is a cheap way to insure a relatively stable voltage into an expensive CRT.


I am going to put a G90 on the bench in the next day or so, and I'll throw a Variac on it, and will take the voltage down to 80 volts or so to see if the HV increases at the tubes. If so, then Terry is bang on with his info. If not, I'm going to suspect that it's a fluke of the strangest kind. I will report back.
 

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Discussion Starter · #5 ·
Curt,

I can't explain this either. But I do know of 5 or 6 instances or tube faces cracking on G90's. 3 of them I have first hand info.


1. The one mentioned in the post below. The first time it cracked a tube there was no UPS and we were having very bad spring thunderstorms here which were leading to many brown outs at the theater mentioned. And then the second time it cracks a tube is when the UPS is out of circuit and the low voltage conditions are found.


2. A European who was running on 220VAC that he was bringing down to 120VAC. Unknown what or how he was doing that but problem went awat after he got the AC voltage straightened out.


3. A customer in upstate NY who had been running for 2-3 years without problem. One spring day bad storms came through and and his kids were watching it, there was a brown out, and the PJ turned off with a broken tube. Replaced tube, put in UPS, two years no problem.


All of these instances are new MEC tubes NOT rebuilds. All of them had an AC power problem that was associated with the tube cracking.


Curt like you this makes no sense to me, and never has. When I first started to hear about these failures even outside the PJ's I was involved with, I tried to understand what was going on here and also tried to duplicate the problem with G90's in my shop and was not successful. If you look there are some posts a few years ago on this where I was trying to methodically look at this problem but never could come to and definitive conclusions,,,,,EXCEPT that running a UPS seemed to make the problem go away.


This final cracking of a tube when the UPS was removed and voltave found to be low and varying depending on what equipment was turned on, further reinforces my conviction that running a UPS is not just prudent but essential on G90's.


Terry
Quote:
Originally Posted by Curt Palme /forum/post/18149221


I'll be odd man out here. I completely respect Terry, but I don't follow the logic, although his experience would dictate merit behind what he says.


Here's my counter:


-The G90s (and 70s) have an auto switching supply that ranges from 100 to 240 volts. They are auto regulating, and are designed to compensate for fluctuating voltages. While I've had a couple of SMPS failures in the G90s so far, I have not traced them back specifically to power surges or brownouts.


-While I have not tried it, I suspect that a low voltage condition to the projector will either shut it down completely, or will result in the HV lowering as well.


-I've had tubes shatter in almost all makes and models of sets, including Ampro, Barco and I've seen one Marquee do it too. With the exception of the old analog Barcos that used to eat tubes, I don't see a set design flaw in any of these sets that would cause repetitive cracks in tubes.


Now, am I going to go as far as saying Terry's info is wrong? Heck no!
I agree with Draganm, a UPS is a cheap way to insure a relatively stable voltage into an expensive CRT.


I am going to put a G90 on the bench in the next day or so, and I'll throw a Variac on it, and will take the voltage down to 80 volts or so to see if the HV increases at the tubes. If so, then Terry is bang on with his info. If not, I'm going to suspect that it's a fluke of the strangest kind. I will report back.
 

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hmmm, maybe you guys are missing something ? Maybe the voltage drop isn't a problem at all,maybe it's the spikes that occur after brown-outs that are causing this? Perspiring minds want to know
 

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Discussion Starter · #7 ·

Quote:
Originally Posted by draganm /forum/post/18156611


hmmm, maybe you guys are missing something ? Maybe the voltage drop isn't a problem at all,maybe it's the spikes that occur after brown-outs that are causing this? Perspiring minds want to know

Could very well be.


Terry
 

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Haven't had a chance to play with my G90 yet, but I will soon..
 

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Guys!


Is this an overheating problem, maybe the fans run too slow?
 
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