Vector guys - what’s happening here?

Griffin

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Years ago I built one of the @dezbaz repro Star Wars graphics boards. It worked but the vector lines were always 'squiggly'. I still have this thing sitting in a box nearly ten years later.

What is happening?

 
Use an ohmmeter, and meter across the traces.

Look around ANY screws, any large components (like caps)

If you see high resistance, look for the crack in the trace. Let's get that sorted first - it can be causing some of this.
 
Years ago I built one of the @dezbaz repro Star Wars graphics boards. It worked but the vector lines were always 'squiggly'. I still have this thing sitting in a box nearly ten years later.

What is happening?

There's some high frequency noise in the X amplifier. Could be caused by coupling from the HV oscillator or some other noise source OR one of the transistors in the amplifier oscillating. That issue in the bottom left if definitely oscillation. Likely the root cause is poor layout of the PCB. When you design PCBs for analog high gain bandwidth amplifiers you have to consider things like trace impedance, current paths, inductive and capacitive coupling and other parasitics. It's no longer just an exercise of connecting parts with copper traces. The issue with the picture disappearing could be many different things I wouldn't even want to guess on that one without a little more info.
 
Thanks for the replies. I have no idea when I will be able to actually work on this board as I don't even possess a vector monitor right now, I was more curious to know if the experienced vector people were interested in the issue and what their takes were on it. I have a set of amplifone boards, color vector brick and ARII but no cpu board or harness at the moment.
 
It was so long ago I couldn't even answer this, I went off a BOM sheet that was being handed around at the time.

If you recall, did it give an part # and did you use that or substitute? Those big wire wound resistors need to be Non Inductive (audio grade) to keep from introducing noise. I recall the wigged out text looking somewhat like that.

Have another setup to try the board with to be sure it's the monitor vs the board for that particular issue?
 
There's some high frequency noise in the X amplifier. Could be caused by coupling from the HV oscillator or some other noise source OR one of the transistors in the amplifier oscillating. That issue in the bottom left if definitely oscillation. Likely the root cause is poor layout of the PCB. When you design PCBs for analog high gain bandwidth amplifiers you have to consider things like trace impedance, current paths, inductive and capacitive coupling and other parasitics. It's no longer just an exercise of connecting parts with copper traces. The issue with the picture disappearing could be many different things I wouldn't even want to guess on that one without a little more info.

I'm not sure I've heard of a major issue like this with one of dezbaz's boards (due to layout, etc). Have you?
 
If you recall, did it give an part # and did you use that or substitute? Those big wire wound resistors need to be Non Inductive (audio grade) to keep from introducing noise. I recall the wigged out text looking somewhat like that.

Have another setup to try the board with to be sure it's the monitor vs the board for that particular issue?
At the moment I really don't have any way to test, even that video I posted above is 8-9 years old. Maybe one day I'll piece together the last bits just to get the whole thing running.
 
Isn't that what this thread is about?

Yes and no... he's got 0 info about any individual pieces of the whole here. I'm simply filtering, based upon my prior knowledge, to most likely cause. Your response discusses the fault being in board design.

Likely the root cause is poor layout of the PCB. When you design PCBs for analog high gain bandwidth amplifiers you have to consider things like trace impedance, current paths, inductive and capacitive coupling and other parasitics. It's no longer just an exercise of connecting parts with copper traces.

I've never heard of issues with dez's boards with respect to bad layout. I'm simply wondering since the way I read your comment it implies the boards are laid out in an incorrect manner. So it's more a question of where you've seen issues with Dez's board design.
 
Yes and no... he's got 0 info about any individual pieces of the whole here. I'm simply filtering, based upon my prior knowledge, to most likely cause. Your response discusses the fault being in board design.
That's the same thing I was doing, not specific to anyone's board (I've had issues like this with boards I've designed as well, I just revise them to correct before I release them).
I've never heard of issues with dez's boards with respect to bad layout. I'm simply wondering since the way I read your comment it implies the boards are laid out in an incorrect manner. So it's more a question of where you've seen issues with Dez's board design.
I don't have any specific knowledge of issues with "Dez's boards" (other than this thread) but I do have specific knowledge of poor layouts that lead to the behaviors I described (including many of my own proto layouts) which I believe is what is being shown.
 
dez boards are more less a clone of the original so i think its unlikely it is a layout issue
 
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