Question about HP Compaq FS 7550 17" CRT Monitor

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Monitor makes annoying screech noise

When applications are maximized or opened more than half the size of the screen, the monitor emits a high pitched screeching noise which will only go away if you reduce the size of application windows or minimize them entirely.

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Re: Monitor makes annoying screech noise

What you are reporting is a problem in the horizontal section of your CRT monitor. Usually this is from a component that is failing in the Horizontal circuit.

Most CRT monitors use what is called scan rectification to develop the voltages required for the different circuits inside the monitor. This puts a strain on the Horizontal Output circuits that are responsible for not only the voltage to the flyback transformer to allow CRT illumination (40,000 or so volts DC), but some of the flyback secondary power circuits are what runs the rest of the monitor. When the components in the Horizontal output circuit get weak and can no longer support the higher demands of the dependant circuits, the flyback transformer tries to run harder. The more current it tries to draw to continue operating, the louder the whine becomes. Since the flyback operates around 17,000 cycles per second, it is in the audible range. Since you can physically hear it, you can also notice the change as the load demand on it changes.
What happens when you reduce the size of application windows or minimize them entirely is the demand on the power circuits is lessened and the flyback circuit is no longer trying to produce the higher demand that it was with the large application windows.

It is a good bet that it will not be too long before the Horizontal output and/or transformer give out completely and leave you with a dead monitor and a large repair bill.
Since it has not gone completely out yet, I would suggest you consult your local repair shop for an estimate. It may be a simple matter of replacing the high voltage capacitors around the Horizontal output transistor before the other parts in the horizontal circuit are damaged. This would certainly be a less expensive alternative.

If you opt to not get it repaired, new 17 inch LCD flat panel monitors can usually be purchased for around $150 or so.

Only you can decide which choice is right for you. At least now you have a few facts to help make the decision.

(I realize I probably gave you more information than you wanted, but I felt it might make things a bit easier to understand. If not, please forgive the disertation.)

I hope this helps.

Posted on Nov 06, 2007

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