Apple II+ Vertical Lines

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Apple II+ Vertical Lines

Hello all,

I recently inherited an Apple II+ (RFI rev), and it seems to boot fine, but it has some serious vertical lines on the video output. I've been troubleshooting to the best of my ability, and have had no luck whatsoever getting it to work. 

Things I've done so far:

  • Replaced UA3, UA9, UB2, UB10
  • Verified correct frequency and voltages on 14MHz, 7MHz and LD194 clocks
  • Verified power and ground connections to the above chips
  • Verified continuity between relevant UA3 pins and the character ROM
  • Tried all 3 rows of RAM in the boot row to verify no chips are bad
  • Resocketed processor and all 6 D/E/F ROMs
  • Tried adjusting video and color trim pots

I'm at my wit's end with this, if anyone has any idea what could be causing it I'd really appreciate the input. I've attached pictures of the board and video output to this post; the video starts out like the first picture with the bars made of dots, but they transition to being solid within a second or two of being booted up, faster if it has been on for a while and only just restarted. Certain keypresses do work so I do believe it's booting up ok, just seems to be an error somewhere in the video circuit.

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Try GR and HGR
  • The fault occurs entirely within the 'window' of the text video generator -- not in the overscan.
  • To the extent that text pixels are displayed, they are not entirely accurate.  There shouldn't be a top "bar" across the letter A.  The top of the letter L is truncated. The top bar is missing from one bracket, the bottom bar is missing from the other.
  • There are three video sources in the Apple ][ and Apple ][ Plus, selected through UA9.  Since you've swapped UA9, that particular component is probably working, so it would be sensible to test the other video sources by using the GR and HGR commands.

Go to BASIC and try typing the GR and HGR commands.  If the video fault suddenly becomes confined to the bottom 4 lines of text (eg: the text window) then it would suggest the fault is in UB2 or something before it, possibly the 2316B "ROM SPCL" at UA5.

Of course the graphics window might exhibit the same fault as the text area...or it might show some totally different fault.  It's worth running the test to find out -- each graphics mode exercises different circuits in a different way.

EDIT: I suggest trying all four screen commands, and noting how each behaves in turn: GR, HGR, HGR2, and TEXT.

(If you don't have the ability to type keyboard commands, then do you have another Apple ][ with a disk drive that could be borrowed?)

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Thanks for the input! Went

Thanks for the input! Went ahead and tried all of those commands, pictures of what I got are below. Going to TEXT from any of the other 3 states produces the flashing seen in the video, GR and HGR give the bottom few lines bars and nothing else, and HGR2 produces the full-screen thinner vertical bars. Given that I've already replaced UB2, I doubt the problem lies there, so would you recommend switching UA5 as the next step?

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GraveFurball wrote:Thanks for
GraveFurball wrote:

Thanks for the input! Went ahead and tried all of those commands, pictures of what I got are below. Going to TEXT from any of the other 3 states produces the flashing seen in the video, GR and HGR give the bottom few lines bars and nothing else, and HGR2 produces the full-screen thinner vertical bars. Given that I've already replaced UB2, I doubt the problem lies there, so would you recommend switching UA5 as the next step?

Wow, there's so much unexpected data in that video that it's hard to unpack it all -- it's hard to guess if there's one complicated fault vs two simple faults that interact to produce complicated-looking effects.

Cataloging some details:

  • Upon playing the video at slower speed (click the '...' menu and choose Playback Speed) the flashing of the cursor doesn't match the flashing of the top-20 text lines.  I can't devise any sensible guesses why the flashing rates don't quite match.
  • Where flashing occurs, it does accurately invert the pixel patterns.  The "FLASH" is generated by the exclusive-OR gate at UB2.  If we suppose that the 74S86 at UB2 is inverting those pixels, then it suggests that the text video stream is already bad before it enters UB2, and UB2 is merely inverting already-bad pixels.
  • In the video, the top 20-lines of the display all contain byte value 00 from clearing the GR screen -- they should be INVERSE @ signs.  So why are they flashing?  Could there be a faulty input pin to UB2?  Ah ha, yes!  Character-flashing is controlled by using UB11 and UB13 to combine the character's value with the high-bit from pin 17 of UA5.

 

There might be faults in those gates at UB11 or UB13, but UA5 just keeps arising as a likely suspect.  This could be a good excuse to upgrade your original character ROM to a lowercase one.  Reactive Micro has replacement firmware ROMs for $10 apiece, so you could choose an original-style "II+ 7341-0036 Character Generator" or an enhanced "II+ Lowercase Generator".  Either of those choices could replace the original 341-0036 in socket UA5.

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I actually forgot to mention

I actually forgot to mention that I already swapped UB11 and UB13 with identical chips from elsewhere on the board to see if the issue would resolve itself (it did not), so all signs seem to point to UA5. Just ordered a new one, I'll be sure to report results once it arrives in a few days! 

CVT
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Why don't you try running the

Why don't you try running the Apple II RAM Test Utility? I think you will be able to see and read the results on the monitor just fine, before the machine has a chance to heat up.

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Fixed!

Kinda fell off the map here, but just wanted to check back in and say that replacing UA5 solved the problem. I've played with it a bit since then, and it seems to be working great, thanks for all your help! 

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