CurtPalme.com Home Theater Forum

[Tim in Phoenix]

Guys!

Some of you know I was the technician for Electrohome CRTs in the Detroit area for many years, with clients like Ford, GM, Chrysler, EDS, U of M, Lear, and dozens of others.

When the Marquees first rolled out in late 1992, Ehome invited near 200 of its' dealer personnel to Toronto for the big news. The Marquee was their first CRT with tubes bigger than seven inches as well as their first magnetic-focussed chassis. The M8000 was to replace the ECP series, with the M9000 as their first LC offering. The M8000 sold nicely after the intro, but we were seeing a lot of soft failures in the neckboards, with the symptom usually streaking, which was determined to be failures in certain small transistors on the neckboards. Tube arcs was believed to be causing these failures.

My life became hell as I had to change out two or three sets of neckboards every day for several weeks, and the replacement boards were failing too. Ehome stopped shipping new projectors to us while they sorted out the problems, which was not good news either.

To study these failures, the Ehome engineers wanted arcs on demand, so they contacted the physics department of a university nearby. Two guys from the university paid a visit to the Ehome plant, discussed what was needed, and they brought a powerful laser on their return visit. By firing the laser at certain points on the electron gun, they would vaporize a small amount of metal and the tube would arc most every time. They could measure the arcs hitting devices on the neckboard, and the appropriate diodes and caps were added for a more robust design.

I am not sure what became of the laser-drilled test machine.


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[1031]

I readet while ago about that prosess.

http://www.research.ibm.com/journal/rd/262/ibmrd2602N.pdf

[r.bauer]

[draganm]

[tse]

Electrohome came up with a really good CRT grounding method for controlling arc current. The copper tape with conductive adhesive placed on the external dag and two flat braided cables coming back to the spark gap ground from there. That keeps the arc current contained where it doesn't cause too much problem. The heck of it is the CRT manufacturer suggests that in the spec sheet but not everyone caught on.

Scott

[Tim in Phoenix]

Say Scott


Are you saying early Marquee tubes lacked the ground straps? It is sixteen years ago and I don't remember.


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[tse]

Tim, I don't know about the early versions. The later ones have the ideal configuration. I've seen alot of projectors that ground the dag to the chassis. That lets the arc current return to the HVPS through anything connected to the chassis. The Electrohome method contains the arc current to the flat braided cables so it doesn't travel through anything that might break from the current surge.

Scott

[Heywood Jablome]

The hard part was getting the sharks with fricking lasers on their heads to keep still long enough for aiming.

[Tim in Phoenix]

Guys!

Another bizarre story unfolded one morning in 1990. Arriving at my office, my partner Bill is just hanging up the phone with a highly pissed customer who says the picture on her ECP 4000 is jumping wildly all over the place. Bill is white as a sheet, she chewed his ass pretty good. He says "You better get over there". There is Lear Automotive Seating, about fifteen miles away. I check in through security and they escort me to a classroom. About thirty people are standing about, and there are rows of tables with PCs filling the room. The ECP is towards the front, and the image is fluttering wildly. I have seen this maybe once before when a slide projector had been used sitting near an ECP.

There is a vague smell of burning plastic.

I knew it wasn't the projector acting up, it had to be external. The ECP is on a table with many wires and outlet strips to power the PCs. The projector and maybe six PCs are all on one extension cord. It is a one hundred foot cord-reel like you would use in your yard with a hedge trimmer. It is ten feet to the wall outlet, so there is maybe ninety feet of cord still on the reel, making for a very powerful magnet. I touch the side of the reel and burn my hand...... The women from the phone walks in and begins cursing me. I tell her to empty the room and turn off all the PCs in front, or else there is about to be a fire. She starts cursing me, they are in the middle of loading much software onto the machines. Then the cord-reel let go and the front row went dead.

Fifteen minutes went by as I let the reel cool down some. Sure enough, when unfurled, it was nicely charred through the middle. The woman starts cursing again like it was my fault, and announced there was no way she was paying for my service call, even though a fire was avoided.........


.

[tse]

It is always the projector that is at fault.......

Scott

[Robert A. Hill]

Scott,
The Ampro 3600s use copper spring contacts from the CRT metal enclosure to the CRT dag coating. Then a ground strap connects the enclosure and neckboard ground ti a ground on the motherboard. Nothing actually keeps the CRT assembly isolated from the chassis. So arc current can go to the HVPS? Is the Electrohome CRT isolated completely from the chassis with rubber grommets or insulators?

[ecrabb]

That's a good story, Tim. The self-righteousness of people - even in their own stupidity and ignorance - never ceases to amaze me.

My dad used to rent motorhomes in the late 70s and early 80s. A few times every summer, somebody would call and be all pissed because "this motorhome is a piece of sh*t - the air conditioner won't work." My old man would ask them how the coach was plugged into the land power, and the reply was usually something along the lines of, "With an extension cord!!! How else do you think I could reach the house?" He'd explain to them that if they'd go out to the driveway, they'd probably find a smoking, smoldering, mess of plastic and copper that probably only looked vaguely like the extension cord they used to trim the hedges with. Some felt stupid, and some were just pissed like it was the motorhome's fault, but very few could believe that was why the air conditioner wouldn't cool the coach.

There are some REALLY stupid people out there.

SC

[emdawgz1]

Johnnys first rule of life.....

"2 out of 3 people you meet are CLINICALLY STUPID"

Nothing is their fault. They are always right. You must always accommodate them.

[Curt Palme]

[Curt Palme]

[Blorton]

Wow! Great story Curt - very lucky there.

re: the cursing woman - I don't believe in hitting women, but I dare any of you to say that a nice solid backhand wouldn't feel pretty damn good in that case.

[Heywood Jablome]

Welcome to the car business... I've been living it for 16 years.

[BobNelson]

Tim:

Tell them about the leaky roof.

[Tim in Phoenix]

[1031]

Here is another story.. My friend moved to new house, before he had dedicated hometheater room. New house had no room for HT room, He thinked that maybe he could build HT in garage, problem is that he is car hobbiest and usually he keeps his old convertibe there, so there is no room for seatin..I suggested that why not do "drive in theatre" Just sit on car seat and wach movies.. Ok he said but we needed something cheap for projector. I founded one guy that had old flight simulator projectors sitting in storage about 5 years. It was quite near to me so i drove there and founded 6 E-Home M8000 projectors, most with worn out tubes, few decent. So i taked extensioncord and powered one of those and it runned quite ok. Now the best part. Storage was old cow shed, there was no heating, air was moist and whole projector had mold inside..And the smell You can image how old cow shed smell´s, air there had so much "acid" that it was miracle that there was copper left on pcb´s
So i had stinky projector back at my car trunk and now it is on ceiling at my frieds garage (cleaned of course)

So Marquee survived there.. what do you think if there was kept digital projectors?