[sci.electronics] death of a friend

todd@uop.edu (Dr. Nethack) (03/13/88)

I have an old adds viewpoint I am using here, and the thing works
fine except that the brightness is all the way down, and there is
still background light on the screen.

Can this be fixed? I don't mind hacking around on the boards.

All I can think of doing is a tube brightener, but that is just impulsive.
Are there some other parts I could fix or replace?

Please help!

Thanks
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+ uop!todd@uunet.uu.net                                               + 
+                 cogent!uop!todd@lll-winken.arpa                     + 
+                                 {backbone}!ucbvax!ucdavis!uop!todd  + 
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commgrp@silver.bacs.indiana.edu (BACS Data Communications Group) (03/14/88)

>I have an old adds viewpoint I am using here, and the thing works
>fine except that the brightness is all the way down, and there is
>still background light on the screen.
>
>Can this be fixed? I don't mind hacking around on the boards.
>
>All I can think of doing is a tube brightener, but that is just impulsive.
>Are there some other parts I could fix or replace?
>
>Please help!
>
>Thanks
>-----------------------
> uop!todd@uunet.uu.net

Loss of contrast, in the absence of streaks, vertical lines, etc., 
usually indicates a worn-out "picture tube."  If the phosphor is 
burned (brown spots in most-used area), then the CRT probably has 
zillions of hours' use and is almost certainly bad.

A "tube brightener" is a transformer that raises the filament voltage, 
to get more cathode emission.  That won't work in most CRT terminals 
because their filaments are DC-powered.

Most monitors have internal brightness-control "trimpots."  You may be 
able to improve the picture by tweaking the screwdriver adjustments on 
the monitor circuit-board.

Electrolytic capacitors are a weak point in monitors.  Look for 
discolored cases and bulged end-caps, especially on capacitors 
associated with power supplies taken from flyback-transformer 
windings. Also look for burned resistors and diodes associated with 
these capacitors.  Replace any nonpolar electrolytics on general 
principle, using non-electrolytic types if possible.

--

Frank Reid
reid@gold.bacs.indiana.edu
reid@iubacs.bitnet

tedk@ihuxv.ATT.COM (Kekatos) (03/15/88)

In article <1260@uop.edu> todd@uop.edu (Dr. Nethack) writes:
>I have an old adds viewpoint I am using here, and the thing works
>fine except that the brightness is all the way down, and there is
>still background light on the screen.
       ----------------
       Do you mean that you can see "rastor scan lines" on the screen?
>
>Can this be fixed? I don't mind hacking around on the boards.
>

Have to tried  playing with the brightness and contrast controls?

I think there is a video signal gain adjustment on the video board.








Ted G. Kekatos
backbone!ihnp4!ihuxv!tedk                     (312) 979-0804
AT&T Bell Laboratories, Indian Hill South, IX-1F-460
Naperville & Wheaton Roads - Naperville, Illinois. 60566 USA