Apple ][+ display vertical repeat plus more mystery

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Last seen: 20 hours 11 min ago
Joined: Sep 19 2019 - 11:44
Posts: 22
Apple ][+ display vertical repeat plus more mystery

Hi.  Another Apple ][+, a new-to-me problem that I am hoping some of you can point me to a solution.

The computer boots, beeps, and displays Apple ][ and the ] prompt.  (No disk controller installed, 48K plus a 32K Saturn RAM card in slot 0).

However the display of the Apple ][ and the prompt are repeated.  Here's a picture:

 

And if I type a little program ...

And try to run it...

You will see that the output, and the list of the program, have changed some characters.

What should I be looking to replace?   

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Last seen: 6 days 14 hours ago
Joined: Aug 4 2018 - 21:59
Posts: 124
Looks like a video counter or

Looks like a video counter or vsync issue.

Check the 74LS161's (D11-14), A12, B11, B13, B14, C13 and C14 .

 

 

 

 

 

 

 

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Last seen: 20 hours 11 min ago
Joined: Sep 19 2019 - 11:44
Posts: 22
Not those chips :-/

Thanks David_M.  I tried all those chips, plus a few more that seemed part of the video path as well.   Not resolved.  All of them worked in a donor system as well.

I am going to try replacing the capacitor at C16.... just reaching for straws at this point.    I don't have an ESR tester or anything, but I have ordered some replacements off of ebay for a few bucks.   I'll report back.  Always appreciate folks giving me advice and tips to try, so thanks!

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