Strange issue with floppy board

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It looks like there is a

It looks like there is a flakey bit or two in the path of the video shift register or out of the character ROM.

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Well it's the best idea I had

Well it's the best idea I had since a long time (and the Apple II is still on my work bench) I'm priting the video address area and will look specifically at shift registers

 

 

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Perhaps you could also try

Perhaps you could also try the suggestions in my earlier posts and report the results. 

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Hi Jeff, Sorry didn't want to

Hi Jeff,

 

Sorry didn't want to ignore you.

The issue disappears once you remove enough chips out of any card for i t to be inoperative.

Eg you you remove the PROMs in the floppy card, the issue disappears

 

Also, the problem is the same wether or not floppies are connected

 

More than than , the line are much less visible when floppies are active (the original poster also reported that)

 

It is super bizarre

 

 

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That could actually be useful

That could actually be useful information. With all of the other cards and the disk cable removed, try removing just the P5 PROM. Then put it back and remove just P6.

 

If the results are the same with either chip removed, then yes it's probably related to the power supply. If the lines go away with just P5 removed, then it could be a timing issue on either the address or data bus. Further testing could narrow that down.

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I'll try to make a small

I'll try to make a small video, altough I'm no youtuber :) 

 

I strongly believe this is more than a PSU problem. However I simply don't have two PSU, and more than that, I don't have a "modern" PSU (like a reactivemicro) to completely rule out the role of the PSU in this.

 

However what makes it unlikely to be "only" a PSU problem is

- the thin line appear perfectly in the middle of the letters. They also don't move or flicker.

- if you look closely, the thin lines contain dots (a bit like a string of morse code) , again, this is more digital noise than a noisy power rail to me.

- removing a single chip (I don't remember which one but i'll update my post) out of the diskII card make the problem disappear.

- multiple people report the exact same problem, the pictures all look super similar, I find it unlikely everyone has a failing power supply that behave s the same accross countries.

 

What does , however ; go in favor of a PSU problem is

- the lines are more visible with each card you add (they are more pronounced, they don't really "change" in appearance)

- On ym oscilloscope ; I can see increased noise, up to 700mV pp, on the 5V rail with each card I add. The 5V rail is noisy - but it may well be "stock noisy", again I don't have multiple PSUs. (Mine is recapped)

- I don't see a direct, visual correlation between the 5V noise and the lines. 

 

And the problem seems to be "monochrome PAL only". So again there is that "timing" issue here.

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