geert@ahds.UUCP (Geert W.T. Jonkheer CCS/TS) (03/13/91)
It occurred to me that many other SM124 owners seems to have problems with their monitor (looking at the news). Well, here's my problem. When ca. 3/4 of the screen is black, i rarely can't read the 1/4 that's white and still on the screen. You know that that will disturb me (especially when I use Minix, which uses a black background, or using programs that are inverting the screen). Has anyone has the same problem, and can it be fixed???? Please help !!!!!!!! Help will be appreciated. Thanks in advance! Geert. ----------------------------------------------------------------------- Geert Jonkheer | UUCP: -> ....!hp4nl!ahds!geert AH CCS/TS Netherlands | Or send the answer to comp.sys.atari.st.tech. -----------------------------------------------------------------------
andyc@hplsla.HP.COM (Andy Cassino) (03/16/91)
| I recently purchased a 'previously owned' SM124 monochrome monitor. It seems | to work quite nicely except for one minor problem. When the display is a | black background and there is very little text on the screen, the image is | quite dim. As more characters are displayed the image brightens as if the | brightness control were being turned up. I received e-mail from one Ian D. Hawkins who apparently can read this group but not post to it. With his permission I am posting his explanation and solution for this problem... "It's easy to fix the fading problem. It's caused by the drifting of the cathode supply voltage. This is fed to the card on the end of the picture tube to a connection marked b2. It should stay at 70 volts, but drifts high when the screen is nearly black. the grid thus appears more negative and so the current drops off. Fix it by regulating the 70 volt line with, for example , a couple of 36v zeners in series. They dont draw much current, only a few mA. V2 and V3 are ground connection on the tube-end pcb." %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Andy Cassino % % Hewlett-Packard - Lake Stevens Instrument Division % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
goo@hpindda.cup.hp.com (Michael Goo) (03/19/91)
Just another data point. My new monochrome monitor does this too, though not to that extreme. Weird. (Hope it doesn't get any worse :-( )
andyc@hplsla.HP.COM (Andy Cassino) (03/26/91)
On the topic of monochrome monitor fading, here's some more information,
received from KREYMER@FNAL.FNAL.GOV:
"I have seen this problem on many monochrome monitors over the last couple
of years. Thank you for the solution to an old, nagging problem !
I have installed the suggested zener diodes on one of my monitors, and
the problem has vanished as advertised. Inspired by this success, I
tried a similar, simpler solution. I have installed a simple 33 kilohm
resistor between B2 and ground. It draws just 2 milliamps, which is enough
to keep the voltage between 68 and 72 volts. The screen is just as stable
as with the zeners, and 33K resistors are a lot easier to find then 72 V
zeners. Any value from 33K to 100K seems to do the job."
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% Andy Cassino %
% Hewlett-Packard - Lake Stevens Instrument Division %
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