TC> I got another question, since you're good with monitors.  This is
 TC> regarding the CTX CVP-5439A 14" .39dp SVGA analog (Tri-sync) color
 TC> monitor.  Since new, its made noises (which is normal) that I was
 TC> always curious about, but nobody has been able to explain technically
 TC> what the noises are from.  They are:
I know those well... I've got one in the workshop at the moment.
 TC> - power up "broomph" like a motor starting or something.  I can't
 TC> explain it exactly, but sometimes on power up it makes a low-pitched
 TC> noise.  Is that that Startup pulse provider you mentioned? Is that
 TC> what is powering up?
That's the degaussing coil. Nearly all monitors make this "boing" at power 
on. All colour screens have it (mono's dont). Degaussing is the process of
clearing the tube of any stray magnetic fields that may have built up on it's 
metal parts (such as shadow mask) which will effect the purity of the 
colours. The "boing" is because the coil is a VERY high current drainer and 
actually acts as a kind of crude loudspeaker - for your 50/60 Hz mains. It 
only lasts a short time as the degaussing pulse is only 1-2 seconds long ... 
it's turned off long before your tube heats up enough to show an image.
The electronic startup pulse is silent in operation. All it is is a resistor 
from the rectified mains input (which is about 330v or so); all it does is 
feed
a few volts DC at a low current to the PSU Switchmode controller IC to 
rovide
it with a voltage rail for the few milliseconds it needs to start up. After 
that, a winding on the psu transformer (with diode, capacitor etc) provides 
power for the chip. It's a "chicken and egg" situation - the chip only runs 
as it has power, yet power is provided by the fact that the chip is 
orking...
so how does it start? via the startup pulse!
 TC> - The old familiar "mode change tweets" - CRT tube adjusting to mode
 TC> or scan frequency adjuster of some kind??
 TC> - The "clicks" during some mode changes (I think this is from high
 TC> to lo res. The tweet from low to high res, or maybe I have that
 TC> backwards). This is some kind of relay to change mode back?
That particular monitor has 2 relays in it. you are hearing the mechanical 
operation of the relays. (A relay is an electricly operated, mechanical 
switch). The relays change state when you change modes.
 TC> I was just curious what those are.  I know if I DIDN'T hear them I'd
 TC> become extremely worried (espeically if the power-on noise didn't
 TC> happen when I turned the monitor on after its been setting more than
 TC> an hour...)
if the degaussing fails, you get colour impurities (eventually) but there is 
no long-term failure. If a relay fails, however, it's service time as the 
image onscreen will be incorrect (too wide/narrow/short/tall/bright/dull) and 
impossible to fix with the user controls.
 TC> RE: High Voltage
 TC> OUCH! That tube we look at? Sheesh! Wonder why they need so many
 TC> volts to operate the screen display? May be the number of times the
 TC> color guns have to fire, huh? And how fast it has to do so (ie.
 TC> scanning frequency).
Nope, irrelevant. The voltage is set by how much energy is required to 
accelerate the electrons from the gun(s) hard enough that they hit the 
screen. Too little voltage = little or no electrons hitting the screen = no 
pix. The size of the tube (15", 14" etc) is important, as is it's length 
front to back, and deflection type (90 deg, flat sq, trinitron etc).
(Remember, an electron is negative and is attracted by a positive charge. 
Without that big + charge at the other end of the tube, the electrons would 
be emitted from the gun equally in all directions, and would then just wander 
aimlessly about (more or less) and very few would ever strike the screen.
 TC> I've worked on "live" computers before. You just have to follow
 TC> one rule - STAY AWAY FROM THE POWER SUPPLY! Don't touch it to
 TC> "ground" yourself (or you just may - literally - if something
 TC> malfunctions). So many installation instructions say "leave computer
 TC> plugged in, but turned off. Touch the power supply to discharge
 TC> static in your body." IMHO, WRONG! That's asking for trouble.
Those instructions are correct. When the PC is plugged in, the metal box of 
the PSU is grounded via the mains cable. When they say touch the PSU, they 
mean, touch it's outer metal case, not "open the PSU's case, touch the stuff 
inside". If the PC was not plugged in, it would not have a path to ground, 
therefore touching the PSU case would be ineffective.
 TC> Anti-static wrist straps, which you can safely screw into a power
 TC> strip's ground are only less than $5 at Radio Shack. I tell folks
I hate wrist straps... not because of technical reasons, they just don't feel 
comfortable, and the ground wire annoys me, and gets in the way. Oh, and 
NEVER screw the ground strap straight to earth. If you touch a "live" part 
with a ground strap on, you provide yourself with a perfect path to 
electrocution... you lose the insulating properties of your shoes etc. ALWAYS 
ground a wrist-strap via a 1 megohm resistor. To not do so is somewhat 
upid.
 TC> I tell folks
 TC> to UNPLUG the machine and use the wrist strap when installing
 TC> cards (like sound cards, memory, modems, etc). That is the safest.
As I said, I never use wrist-straps. I fix probably 20 pc's a day (on a busy 
day) and never have issues with static.... but then again I meet plenty of 
users who blow stuff up trying to fit it themselves (usually as in "i bought 
this, tried to put it in and it didn't go" types).
 TC> I wish computer manuals would stop preaching unsafe working habits.
Not at all. There is nothing unsafe in them what so ever.
 TC> CH> safety devices & practices such as isolation transformers, CRT
 TC> CH> dischargers, capacitor dischargers, eye protection, and TEST before
 TC> CH> TOUCHtechniques.
 TC> Ah... so you DO have protective devices, much like the electric
 TC> company workers have when working on high voltage power lines?
Of course, but they're not "foolproof". You'll still get a nice kick in the 
pants if you do touch something live... all they can do is lessen the current 
drawn, which means a much lower chance of death or burns etc.
 TC> the #1 rule of electronic repair:
 TC> If you are not sure, DON'T DO IT! Have someone else do it. I usually
 TC> ask someone who knows and if I still am not sure about poking into
 TC> the unit, I take it to someone who has done lots of that type of
 TC> work and have THEM do it. Either that or buy another, or (more often
 TC> than not) make do without the unit. 
Yup... a good policy. I often think to myself how much hassle, time and money 
users could save if they had their stuff professionally fitted in the first 
place, instead of briniging my their aborted, damaged stuff and spending a 
_lot_ more to fix it properly.
       Craig
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