Strange issue with floppy board

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Joined: Feb 14 2021 - 19:22
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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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Apple europlus vertical bars again

Just joined to say I have a europlus (UK) attached to an apple monochrome monitor with exactly the same issue of the row of vertical dots down the center of each character row. Only occurs when I plug in the diskII controller and gets worse when other cards are added. PSU is recapped on input and output side. This PSU has no Y2 filter from the factory. I presume no one has managed to get to the bottom of this so far?

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I solved a similar issue on

I solved a similar issue on two machines.

First machine I upgraded the power supply to a ReActive Micro supply, and I never did notice, but looking at it now there are no vertical lines (they were faint to begin with)

The second machine I replaced the video connection train.  New jacks on motherboard and monitor (the old ones were horribly dirty and oxidized), different cable -I used a sheilded SPDIF digital cable (which is compatible).

I also adjusted the output potentiometer on the motherboard.  The combination of all these things dminished the effect to almost imperceptibility.

I have also found that sometimes this is monitor specific - perhaps has something to do with the monitor's input impedance that can pick up noise in the signal and display it.

 

Tricky problem.

 

 

 

 

 

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This could indeed be monitor

This could indeed be monitor related. I'm using an apple green screen monitor with a well shielded modern cable.

I've turned the brightness up on the apple onboard and turned the brightness on the monitor down and I can get a perfect picture and not see the dots.

 

If I run the signal into a cheap HDMI converter to an LCD monitor while the picture is not as nice as the green screen there is no evidence of the columns of dots whatever I do with the brightness on the apple.

 

I do however also have an apple IIe and it does not have the issue at all on the green screen. Obviously quite different video circuit. (Both are UK/pal)

 

 

 

 

 

 

 

 

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