AVR-Chat

Arir,

To me, without knowing all the details, it sounds like Power Supply issues
as all symptoms can be effected by the power supply. That gives you a commom
factor. At least it's a place to start. Using your trouble shooting O-scope
and voltage meters you should be able to track it down.

1. Focus Voltage -- Does it change when symptom occurs?  ( Power supply
weak?) Meter time here.
2. The pulse generated in the system can be noise in the power supply as
well. Scope the Power supply lines to see, if you see it there you can trace
it back to the source or temprarly filter it out. If it's a new design,
decouping suppresion caps may not have been used or the selection may be
incorrect. The power supply lines is where that sign can sneak into the
whole system.
3. The wave form flickering could be noise on the the signal circuits
induced from the power supply to them. Scope those   power supply lines.
4. Typically when losing focus when moving the displayed wave form from the
center of the CRT , the deflection plates need more power to do that. (ie.
loss of focus if trace is move away from the center of the CRT), I would
again suspect something with the power supply in. If the trace can be moved
back to the center of the CRT and it regains focus, that's a hint.
5. The --- Noise--- you mention, if you have confirmed that the noise is
patternized, what circuits are common to it if you have ruled out that it's
not getting in the power supply. ( Don't forget your harmonics here )

Typically Focus and Anode voltages are Higher voltages in the past were
separate supplies from the circuit supplies. However, today most low
voltages for the circuits are flyback derived, so separating the two is not
as easy.

You stated you suspect Ground issues, this could be, Remember Ground is the
return path for the Power Supply (Which means it is a part of Power Supply.
Solid Grounds are a must for all power supplies. Don't forget there can be
multiple grounding points incorperated into a system, which may not have a
common point.

If a problem wiht your device seems to big to understand, break it down into
smaller pieces that you can understand.

Divide and Conquer.

Good Luck and Regards,
Mike Benoit




----- Original Message -----
From: "Arif YILMAZ" <arif.yilmaz@bilten.metu.edu.tr>
To: <AVR-Chat@yahoogroups.com>
Sent: Monday, December 05, 2005 12:41 AM
Subject: [AVR-Chat] Driving Oscilloscope CRT like Memory Mapped Graphic
Display


> Hello to all Experts,
>
> I would like to refer to your information about oscilloscope CRTs. I
> have to use a crt do display waveforms like an oscilloscope but having
> really big problem with this sacred device.
> I used already available crt driver circuit with transistors and my
> waveform seem very stable and nice when I inspect it on a scope, however
> I cant get such stable view when I look into the CRT display I am trying
> to drive.  The waveform flickers when I touch CRTs shield, its focus is
> lost when I move the waveform vertically etc.  i.e. there are problems
> with the physics of the device.
> I generally have focusing and grounding problems and also it is
> very sensitive to noise for example,  from a pulse signal generated
> somewhere else in the system.
>
> Well, I would like to hear your experience on such issues, and I
> really would like to know if there is already available chips to drive
> such problemmatic device ,
> and if there is any available chips to drive it like a
> monochrome Graphic display?
> And also manuals tutorials on CRTs would be helpful,
>
> Thank you for your interest in advance...
> Arif
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> Yahoo! Groups Links
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