Re: Apple //c

[mjmahon@aol.com (Michael J. Mahon)]

Ralph Glatt responded:

>mjmahon@aol.com (Michael J. Mahon) wrote in message
>news:<20010610041535.13698.00007451@ng-ch1.aol.com>...
>> Ralph Glatt asked:
>> 
>> >I have an Apple //c that has a problem with it's video. The words keep
>> >sliding off to the right, starting at the bottom, and slowly going to
>> >the top. I tried the monitor on a different //c, and it worked, so I
>> >know it's not that. Is there anything I can do, or should I just use
>> >it for parts?
>> 
>> Could you be a bit more descriptive about what "sliding off" means?
>> Does it look like a TV with a marginal horizontal hold problem?
>> If so, then you probably have a monitor with a marginal horizontal
>> hold problem.  ;-)  You may need to take it apart to find the hold
>> control, which could be an issue.
>> 
>> Do the words "slide right" a bit, and then come back, as words
>> higher up the screen slide, in a long cycle?  That could be a hum
>> problem, caused by a nearby transformer--is the //c "brick" close
>> to the monitor?
>> 
>> Or is the "raster" solid, and the dots that make up the letters
>> "slide" to the right.  That would be a _very_ interesting video
>> problem for a //c!
>> 
>> Do you have another monitor to try?  Or a TV modulator?
>> 
>> Say more about your problem...
>
>Hi, Mike, thanks for answering. I had already stated that I tried the
>monitor on another //c, and it worked fine. By sliding off, I mean it
>looks like it's a horizontal hold problem, but I don't see how it
>could be the monitor. When I hooked it up, I used the same cables and
>power brick as the good //c.

Trying another monitor on the possibly misbehaving //c is different
from trying the same monitor on another //c.  I suspected marginal
horizontal frequency adjustment on the (sometimes) failing monitor.

>I just tried it again, and now it works fine. Still, I have to wonder
>why it was doing that. I know it was sitting for a long time, because
>I found it in a second hand store, and it looked like it had been in
>somebody's closet for the past 10 years or so.

This pretty well confirms my suspicions.  If you are comfortable
getting inside a monitor, of have a friend who is, just adjust the
horizontal hold control while displaying a full page of text.  Find
the "edges" of the range where the picture "tears" or "breaks up"
and set the control to the middle of this range.

It sounds like your monitor may also be temperature sensitive.
A little of that is not unusual--which is why it's best to let the
monitor warm up before making the horizontal hold or vertical
hold adjustments.  But a lot of variation with temperature is a
sign of a component headed west--most likely a capacitor in
the horizontal oscillator circuit or (often) an electrolytic in
the power supply or boost supply.

With any luck, it's not too temperature sensitive, and a simple
hold adjustment will make it solid as a rock.  ;-)

-michael

 Email:  mjmahon@aol.com
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