PDA

View Full Version : Monitor



robharv
27-05-2003, 05:47 PM
During work and standby my monitor works fine but on shutdown with the monitor switched off, after a period, it starts an intermittant buzz which can only be rectified by switching off the power supply.
Any ideas?

Billy T
27-05-2003, 07:11 PM
Hi Rob

By switching off the power supply, do you mean at the power point on the wall? The on/off switching on modern moitors can be either mechanical or electronic, but either way, once off the majority of the monitor's innards are without power.

The noise you hear may be from the input power filtering which is always live so long as the power plug is in a live socket. The filter consists of an arrangement of capacitors and inductors (coils) but in the absence of current flow, the inductor canot make any noise. Capacitors can, however, as they often possess piezo-electric properties (same effect as used for "crystal" microphones and ceramic pickup cartridges. Modern uses for piezo-electric ceramics include positioning for mirrors in optical systems, head adjustment and other motorless drive systems.

Anyway, it is possible that one or more capacitors in the filter input to your monitor may be vibrating mechanically in sympathy with the input mains voltage. Alternatively, there could be a defective joint that is arcing slightly, and this would also excite noise out of a ceramic component.

Without knowing morabout the circumstances that is my best guess as to the source of the noise. Other information might suggest or identify an alternative reason.

Try listening to the area around the mains plug into the rear of the monitor (or the cord input if there is no plug) using a length of plastic tube as a stethoscope. That may help narrow down the location.Cheers

Billy 8-{)