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Old 9th Apr 2012, 5:00 pm   #1
Lucien Nunes
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Default The spooky tale of the monitors in the crypt

Because CRT monitors are increasingly becoming a 'vintage' technology, I thought I'd post about this here, where lots of people actually understand them!

On film sets it is customary to set up monitors for certain people, especially the director and script supervisor, to see what the cameras see without having to look through the eyepiece. With cine cameras, a miniature video camera is built into the eyepiece optics, in the case of electronic cameras the main output is used. These are connected to a recording / editing / compositing / archiving system operated by the video playback department, independently of the camera assistants.

A playback operator called me from location in an old church where a three-camera shoot was taking place in the crypt. Due to the limited access and difficult working conditions, none of the nine monitors they had taken down onto set was very large. They were all Sony and JVC professional CRT models known for their performance and reliability, including 9, 15 & 17 inch versions. The operator remained with his control station at ground level where further and larger monitors were also located. Multicore cables had been run out from his equipment to the various groups of monitors and cameras below ground, all of which worked perfectly when powered up.

Shooting had begun and at first all was well. The crypt set was dimly lit as the scene was to be played by candlelight and the images shown on the monitors were dark and moody, as the operator saw from the many LCD screens built into his rack. After some hours, he began to get reports on the talkback that the pictures downstairs were too dark, to which he remarked that the camera output appeared correct for how the scene was lit. Nonetheless the director had the operator's assistant readjust his monitors. Not long afterwards, someone else reported that three monitors had started to display a strong red colour cast. Despite the darkness of the vault in which they were stationed, their images soon became too dim to view properly and almost entirely red. Whilst the playback team tried to locate the suspected cable damage, these plus three more faded almost to black.

Nothing could be done at the time due to the difficulty of access, however the monitors above ground and at the control station continued to function normally therefore work continued. As and when possible, new multicore video cables and power feeds were laid on following a different route. The playback crew were alarmed to discover that these made no difference; all affected monitors continued to give only a feeble red picture. New monitors were taken down, which when connected to either the new circuits or the old gave perfectly good performance. Electrical damage to the original monitors was then suspected, especially when one was brought to the surface for testing and found to be dead. At this point the call came through asking whether I could visit the location that evening to conduct a post mortem.

While loading my test equipment into the car, another call reported that the new monitors were also starting to darken. I put on some speed and reached the church at dusk, where I was led through the gloomy and almost deserted nave, down the narrow staircase into the crypt. Instead of cold, damp and desolate as it probably is most of the time, when we reached the bottom we found a bustling underground town, hot and stuffy from the heat of the lights and equipment and haze from the obligatory smoke machine. By now the remaining monitors from the first group plus all but one of the replacements had succumbed to the disease. Their average survival time in the crypt had been just a few hours.

To be continued...

Lucien
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Old 9th Apr 2012, 10:59 pm   #2
Framer Dave
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Default Re: The spooky tale of the monitors in the crypt

Sounds like the beginning of a good yarn, Lucien. Looking forward to Part II!
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Old 9th Apr 2012, 11:18 pm   #3
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Default Re: The spooky tale of the monitors in the crypt

Those smoke machines used to work by vaporising an oil-based substance. I don't suppose it's getting into the monitors and being 'cracked' somehow (by the EHT ?) into something red/brown which is a) plating onto the CRT to change the colour and b) coating the electrics, resulting eventually in their expiry ? Just a thought ...

Cheers,

GJ
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Old 10th Apr 2012, 12:04 am   #4
Lucien Nunes
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Default Re: The spooky tale of the monitors in the crypt

Smoke machine smoke is a nuisance in the long run, because a thin sticky film can build up on surfaces over time if the concentration is high. But it does not and must not cause electronic malfunctions, otherwise theatres and music venues would be unable to use it.

The pictures turned red due to an electronic issue, not something red on the screen. There were various other electronic devices such as PCs and their monitors, sound equipment etc also in use in the crypt. This all worked fine, only the video playback department's monitors were affected.

Lucien
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Old 10th Apr 2012, 3:06 am   #5
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Default Re: The spooky tale of the monitors in the crypt

After using smoke machines in venues, I can confirm the fluid nowadays is glycol (burning sugar) which causes massive problems with optics or anything with an internal fan.
Amps suffer when used in a smoky environment as do video projectors, namely CRT units!
It is unlikely that the smoke machine ******** up the screens, the time when it could do damage is if the room is filled up with a very dense fog/smoke, by then though, poople would have had to evacuate the place, too much glycol upsets breathing and eyes!!!

Last edited by Glowing Bits!; 10th Apr 2012 at 3:11 am.
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Old 10th Apr 2012, 10:05 am   #6
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Default Re: The spooky tale of the monitors in the crypt

I'm guessing its a strong magnetic field causing shadowmask/aperture grill distortion. Maybe it's encased in iron which has become magnetised over the years?
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Old 10th Apr 2012, 10:19 am   #7
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Default Re: The spooky tale of the monitors in the crypt

Hmmm...I'm guessing that the monitors were the only equipment in the crypt involving high voltages. So here's my theory: condensation from the hot, stuffy atmosphere getting on to the monitors' PCBs, maybe affecting the first anode voltage, and then auto-greyscale struggling to keep the RGB drives correct as the operating conditions change, and finally running out of steam and turning everything red? It's a long shot...
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Old 10th Apr 2012, 5:34 pm   #8
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Default Re: The spooky tale of the monitors in the crypt

Maybe high humidity thanks to a lot of people breathing in a confined poorly ventilated space, and spark gaps on CRT base starting to leak or flashover.

John
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Old 10th Apr 2012, 10:30 pm   #9
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Default Re: The spooky tale of the monitors in the crypt

Does sound like a combination of both heat and humidity.

You said that one of the monitors was found to be dead when brought to the surface, what about the others?

Did any of them recover when they were back on the surface for some time?

Were the monitors affected all of the same type?
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Last edited by MrElectronicman; 10th Apr 2012 at 10:32 pm. Reason: Added word for clarity
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Old 14th Apr 2012, 8:00 pm   #10
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Default Re: The spooky tale of the monitors in the crypt

Were there any LCD monitors in the crypt and were they affected?

Is the church near any railway lines?
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Old 15th Apr 2012, 12:51 pm   #11
Lucien Nunes
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Default Re: The spooky tale of the monitors in the crypt

Sorry to leave the cliffhanger up for so long - got stuck on a job in Italy with little time to use the comp. Anyhow a couple of the suggestions almost hit the nail on the head...

The monitors removed from the crypt did not work correctly at first, although a few of them had improved slightly by the time they reached the workshop. Proper greyscales were only restored after repair. Other equipment such as LCDs worked perfectly throughout.

People have mentioned condensation / humidity causing leakage. I had thought about this after the first call but dismissed it as the sole cause, for two reasons. First, the monitors had worked perfectly for some time before the fault appeared, yet under normal operating conditions once the chassis is up to temperature it is almost impossible to form condensation inside due to the temperature rise in the air passing through the monitor. Flight-cased monitors typically run with restricted cooling anyway and attain quite high internal temperatures. The other reason was that I have extensive experience of these models of monitor (there were four models involved) operating under arduous conditions; in the Sahara desert, at sea in a storm, in a tent for a month in continuous rain, etc. without ever having experienced this behaviour. Heat, likewise, does not normally cause problems with these chassis. They have generously-rated electrolytics designed for years of 24/7 operation and can endure much higher temperatures than the people using them.

Leakage, however, was certainly the cause of the fault. Soon after arriving on site, I opened one of the monitors and blew a hairdryer around the LOPT and tube base card to see whether moisture did play any role. The picture immediately improved, although the greyscale remained rather unsteady. Running a cotton bud around the tube base connections revealed a deposit of dust that was unusually dark in colour. I folded a clean piece of writing paper and ran it across the screen like a squeegee, from which it collected a similar dark variety of dust. This I tested with a Megger on 500V, obtaining a reading of just 2MΩ across a half-inch strip even with poor contact at the probes.

It seems that the atmosphere in which the monitors had been operating had a particularly effective recipe for causing leakage. The smoke-machine smoke, while being harmless in isolation, concealed the presence of a very small amount of pure carbon lampblack from the candles. Due to the low air turnover, the CRT monitors were electrostatically precipitating the carbon onto their HT and EHT areas, where it was bonded by the cracked oil and formed into unusually conductive paths by the moisture, despite being below dew point. The EHT was geneally unaffected due to being very well sealed, while the focus, H-stat and A1 / G2 were all subject to more or less leakage from their connections. Most affected was the G2 supply on the Trinitrons. Leakage was occurring from around the pot shafts on the tripler and across the tube base card, not only to earth but also to the tube cathodes with obvious effect on the beam currents. The deposit was generally too thin to see with the naked eye although once collected on a cotton bud it had the telltale dark colour.

The final cure was to carefully clean all HT / EHT parts, the tube base and neck etc. with alcohol and reseal / regrease where needed. A total of 16 monitors had to be processed this way, all of which have worked perfectly since. None of the other equipment was affected at all, indeed it was almost impossible to find anything else on which the carbon had deposited.

Pics below show one of the older (2005) Sony 9" monitors, a PVM-9042 with the S-M1C chassis, before and after cleaning. The effects on the later and larger models and the JVCs were almost identical.

Lucien
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