Monitor Trouble

Depending on how the CRT lost its vacuum, and if anything is shorting or not inside the CRT, will determine if there will be an actual short when putting the power on to the monitor.

Buy your description, it sounds like the CRT was damaged, and air got inside. In this case, your monitor is considered to be, "scrapped"!

If you were able to find a CRT and replace it, you may find out the hard way that something else may also be damaged from the fall. It does not take much to break pieces in a monitor from being dropped.

--

Jerry G. ======

I have a Smile International CB0913DL, which is a very small color SVGA computer monitor. The other day, it fell off the top of a mini-tower computer case that was sitting on a concrete floor. I tried to catch it and partially succeeded. It hit as softly as one could expect, but I thought I heard something go "hissssss" when it landed.

It was not powered when this happened. I'm not even sure I really heard a hissing sound, as the room air conditioning was on and it is loud. Looking inside the monitor, I can find no sign of damage or broken glass anywhere on the picture tube. The circuit boards are all tightly in place and everything looks good there. All the interconnecting cables are in their sockets and I haven't been able to find anything that was loose or intermittent by prodding the boards with the power on.

The monitor does turn on normally and the controls respond when pressed. I've just got no sign of a picture whatsoever, and there isn't even a flash on the screen when turning the power off. (The monitor always flashed when turned off before this.) The CRT heater does appear to be running. The only trace of damage I found was a piece of case plastic that was already cracked.

My question--if the CRT had lost its vacuum in the fall, wouldn't there have been a show of sparks and other violent signs of failure when I powered the monitor? Would the heater in the tube still be functional? I'd have expected it to burn out quickly.

William

Hi!

That's good to know.

Ah well. I didn't have much in it, that's for sure. It's actually a very tiny display, used in applications like POS terminals or similar. To my surprise it would sync perfectly at 800x600 without issue. It had a good picture, but the screen burn was terrible. I could still read the log-in screen text of whatever kind of a system it had been attached to.

At the time, I could have bought a whole trailer of them for pennies on the dollar. I just didn't believe the guys selling them when they said the monitors were color. Now I wish I had--these seem to be somewhat hard to find. :-( Of course, none of them were pretty. All of them had screen burn and most looked like they'd been used in a basketball game, including this one. I guess it just finally had enough.

Curiously enough, the electronics all seem to be *fine*. I've got high voltage, the CRT heater is running, the energy saver LED will come on after the computer should turn off the screen, and all the controls respond by turning on the LEDs in their buttons when pushed. Perhaps even more curious--this monitor does not have OSD (it was made in 1995) but it does have a dedicated board for the control pushbuttons that uses an 8051 microcontroller in a socket. That seems like a lot of "horsepower" for such a simple task.

William

I have *never* seen a CRT that has lost its vacuum, continue to have a visibly functional heater. As you surmise, it is normal for it to burn out immediately. Likewise, it is common to see fireworks in the CRT neck, particularly with small ones where the inter-electrode gaps are small. Somewhere on the CRT neck, you might be able to see the gettering flash deposit which, if the CRT has taken air, will be white rather than shiny brown. However, sometimes, the getter element hangs down inside the bowl, so you can't see the deposit. A few voltage checks at the A1, grid, focus anode and cathode pins, should tell you the story of why there is no display

Arfa

Check for the getter flash inside the CRT neck. There should be an area of likely shiny metallic coating somewhere inside the glass envelope and it may be visible near the base. If it is present, the vacuum is intact. If there is as area of white or red or brown, then it's broken.

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