Apple ][+_ Working but showing horizontal bars

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Apple ][+_ Working but showing horizontal bars

Hi,

  I got an AII+ that appears to be working. It seems to boot, and I can type and see moveemnt on screen.

It is just the main board with only 16K installed. No cards

But there are horzontal bars inplace of charaters.

I have a working AII+ next to this one. I have swapped EVERY chip between them. The working AII+ still words fime.  The broaken one still  shows horzonal bars.

I can not see any evidance of damage to the front or back of the main boed. There has not been any after market work done. All solder points appear the same. and in good condition under magnification. But I may not be able to see a bad joint.

I might have folded a pin inder a chip, but I can't see any evidance of that.

I am looking for some help as to where to look on the board for problems.

The system was a storage unit find. The board was very dusty and had some cobwebs. Most chips pins, and the slots contacts show corrosion. I, of course, dusted and the baord throuighly befor any work started.

 

Thoughts,  suggestions?

Thanks

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Character rom?

Character rom?

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swapped it with chip from

swapped it with chip from working booard. No change.

I swapped every chip from working board to bad board. Bad board still not working, Good board still working.

ANything else I can try?

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Joined: Sep 3 2005 - 04:23
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Would check out this page,

Would check out this page, and posiisbly concentrate on the stuff to do with the character display.

http://www.appleii-box.de/D04_resurection.htm

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Many thanks, but I have been

Many thanks, but I have been all through that page

http://www.appleii-box.de/D06_resurection.htm

This is a better link for it, btw

 

I'm stuck.

If I swapped every chip, it much be a cap, or transistor, or resistor. But how to test those?

 

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Last seen: 1 day 8 hours ago
Joined: Sep 3 2005 - 04:23
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Have you carefully looked for

Have you carefully looked for any damaged traces, or even gently flex the board to see if anything changes.

Also, can you confirm that the same character keypess produces the same pattern block on the screen?

Finally, do some set of charcters produce the same pattern, while others produce another pattern, or are all patters different...it may give you some clues if you check the binary for the keys pressed. Just a thought.

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Your first problem is that it

Your first problem is that it's stuck in lo-res graphics mode - that circuit is fairly simple - check the 8 bit addressable latch at F14, pin4 and work through the graphics system from there (B13, B8, etc) or back to the processor if F14, Pin 4 indicates it's in graphics mode.

 

regards,

Mike Willegal

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DSCN3650.JPG

Thanks,

  The key presses a key gives the same patterm. There is a differnt parrtern for each key.

No change with flexing teh board, with and witout power.

Swapped F14 with working board, no change. swapped F13, & F12. no change. I am not sure how to trace the signal back to cpu. Other chips I could recheck?

 

There is a patch wire on the back and a cut trace to the right two solder point below the top wire connection. But this looks factory made to my primitive eye. This is near the video output. thoughts?

 

 

 

 

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