eric@oakhill.UUCP (Eric Quintana) (10/23/90)
* (I accidently posted this to comp.sys.amiga as well, sorry)
Here it is -- How I fixed my 1950 vertical jitter problem.
The problem was this:
The 1950 monitor will sometimes jitter the screen vertically one scan line.
This problem is intermittent, but usually requires the monitor to be powered
on for an hour or so (monitor dependent -- some show the problem earlier).
The resolution you use does not matter, however I found that a hi-res with
interlace (and the deinterlacer on) is more susceptible. (The default
A3000 workbench settings for resolution and color show this problem.)
What to do:
First, try adjusting your vertical hold.
Next, try adjusting your vertical center. Surprisingly, I found that this
adjustment affects the jitter.
Third, try adjusting the deinterlacer (as per instructions in the small
white book). This adjustment has a range of about 15 turns; during most
of that range, the screen is just fine (except for the jitter). In fact,
I found that the deinterlacer has no effect on the jitter problem, but
you should make SURE your deinterlacer is not the problem.
If you still are seeing the jitter (and it bothers you), below is a
description of how I made an internal adjustment on the monitor to
remove the vertical jitter.
Disclaimers follow:
If you do not know what you are doing, I DO NOT advocate that anyone open
their monitor, for the following reasons:
- Let me quote Scott Hood at Commodore "You should note that your
monitors are covered under the one year warrenty period and if
they need fixing your dealer should handle it or an authorized
repair center."
- The high voltage warning sticker on the back of your monitor is
there for a reason. When turned on, some wires have 10,000+ volts.
A friend of mine touched his screwdriver to a wire and we could hear
the sparks arcing THROUGH the insulation.
- If not careful, it is relatively easy to break something as you remove
the case. The last thing you want to break is the back of the picture
tube.
- Finally, I am NOT a TV repairman. Without a technical reference,
there is no way for me to know that the adjustment below is the
"correct" way to fix the problem. The adjustment is my best GUESS
at fixing the jitter.
Still want to open your monitor? Ok, here goes.
You will need a 2-point phillips screw driver with a shaft longer than
4 inches. You need this to reach the screws at the top back of your monitor.
Odds are you don't have one. Neither does your hardware store. Either
get one from a friend, or buy one from an electronics supply store.
Disconnect the power and computer from your monitor. Remove all of the
phillips screws on the back of the monitor. Do NOT disconnect the monitor
base (or foot -- the thing that swivels). CAREFULLY remove the case.
Try not to break the back of your picture tube. Note that the control
knobs on the side of the monitor are not part of the case, so don't try
to move them.
(I actually placed the monitor face down (picture tube down) on top of a
large cushion. Then removed the case by lifting it STRAIGHT up.)
If the monitor is face down on a cushion, stand it up on its base again.
Reconnect it to the computer and power. Make sure you are not touching the
inside of the monitor. Turn it on.
If you have curious hands nearby, or a pet who seems to get his tail in
everything (my cat does), throw them out and lock the door!
Now, the first step is to get the thing to jitter again. You cannot
make an adjustment until it does. This could be a long wait.
(Of course it will never jitter now that YOU are the repairman :-)
Make sure you disable screenblank if it is on.
Once it starts to jitter again, you may want to adjust the vertical
center to make the jitter as BAD as possible. Remember, adjusting the
vertical center affects the jitter (I don't know why).
Now make the adjustment with the BAD jitter on the screen. You will use
the small tool Commodore gave you for adjusting the deinterlacer. The POT
you will adjust is on the side of the monitor directly below the vertical
hold knob. (If you don't know what a pot is: on my monitor it's a black
round thing with a slot in the center so you can adjust it by turning it
with a screwdriver.)
Note that you may wish to memorize the position of the pot before you start
(ie. mark it or write it down) in case you want to simply return the pot to
its original position.
To make the adjustment, use the deinterlacer tool to turn the pot slightly.
A 16th of a turn should show a change in the jitter! If the jitter returns,
try turning it a little more. (I personally turned mine an 8th turn to the
right. My screen has been rock solid ever since.)
Give the monitor some time to adjust to its new setting (several hours).
If it seems to be solid: power down, disconnect, reassemble, don't break
the picture tube, reconnect, power up, and viola! Good as new.
(You might want to re-adjust the vertical center.)
I wrote this article to be a little tongue-in-cheek, but realize that
opening your monitor is SERIOUS business. Reread the disclaimers above,
and if you break something, I'm truely sorry.
Eric Quintana eric@rorschach.sps.mot.com
Motorola Microprocessor Designpoirier@ellerbe.rtp.dg.com (Charles Poirier) (10/24/90)
In article <4064@rorschach.oakhill.UUCP> eric@rorschach.UUCP (Eric Quintana) writes: >Disclaimers follow: > >If you do not know what you are doing, I DO NOT advocate that anyone open >their monitor, for the following reasons: > - Let me quote Scott Hood at Commodore "You should note that your > monitors are covered under the one year warrenty period and if > they need fixing your dealer should handle it or an authorized > repair center." > - The high voltage warning sticker on the back of your monitor is > there for a reason. When turned on, some wires have 10,000+ volts. > A friend of mine touched his screwdriver to a wire and we could hear > the sparks arcing THROUGH the insulation. >Still want to open your monitor? Ok, here goes. This caution needs to be added to. Some wires still have those 10,000+ volts EVEN AFTER THE POWER IS TURNED OFF and this very high voltage can persist for DAYS due to charged capacitors. These voltages can ARC through 1/4 inch or more of AIR. If it discharges through your body, it will likely kill you. There are ways to discharge the capacitors but I couldn't (and wouldn't try to) say how exactly. So, if you *still* want to open your monitor, be very cautious and STAY AWAY from the wires, especially the fat, well-insulated-looking ones. Be careful in there, Charles Poirier poirier@dg-rtp.dg.com
a309@mindlink.UUCP (George Lin) (10/26/90)
> poirier@ellerbe.rtp.dg.com writes: > This caution needs to be added to. Some wires still have those 10,000+ > volts EVEN AFTER THE POWER IS TURNED OFF and this very high voltage can > persist for DAYS due to charged capacitors. These voltages can ARC through > 1/4 inch or more of AIR. If it discharges through your body, it will > likely kill you. > > There are ways to discharge the capacitors but I couldn't (and wouldn't try > to) say how exactly. > > So, if you *still* want to open your monitor, be very cautious and STAY > AWAY from the wires, especially the fat, well-insulated-looking ones. > > Be careful in there, > Charles Poirier poirier@dg-rtp.dg.com Watch out for the power capcitors or wear a rubber glove. :) ------------------------------------ George Lin a309@mindlink uunet!van-bc!rsoft!mindlink!George_Lin
aduncan@rhea.trl.oz (Allan Duncan) (10/26/90)
From article <1990Oct23.181851.15787@dg-rtp.dg.com>, by poirier@ellerbe.rtp.dg.com (Charles Poirier): ... > This caution needs to be added to. Some wires still have those 10,000+ > volts EVEN AFTER THE POWER IS TURNED OFF and this very high voltage can > persist for DAYS due to charged capacitors. These voltages can ARC through > 1/4 inch or more of AIR. If it discharges through your body, it will > likely kill you. ^^^^^^ Not really, give you a nasty shock and maybe a small burn at the arc point, that's all. However, if you had an iffy heart, it might foul up. Not worth the risk of deliberately being careless though. A point of interest, if you plot death rate against voltage and frequency, it has a peak at 50Hz and 240V (or thereabouts), just the supply system in this country (and Europe)! There are many cases of survival of _direct_ contact with 22,000 volt lines - the usual cause of death is burns, not electrocution. This is because the heart is clamped by the high current, then released when the breaker trips or contact is lost. 50uA of 50Hz through the heart sends it into fibrillations where it doesn't pump. In this case the medicos use the equivalent of the stored charge in the monitor to stop these! Allan Duncan ACSnet a.duncan@trl.oz (03) 541 6708 ARPA a.duncan%trl.oz.au@uunet.uu.net UUCP {uunet,hplabs,ukc}!munnari!trl.oz!a.duncan Telecom Research Labs, PO Box 249, Clayton, Victoria, 3168, Australia.