Horizontal bars on the Apple II+ screen

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Horizontal bars on the Apple II+ screen

I have a problem with the Apple II+ motherboard(RFI) which I restored and had been working well without problems so far. The problem occurred yesterday.

The symptom was that the HGR mode became unstable and the screen was slightly flickering. I summarize the symptoms after restart. With reference to previous posts

, I inspected the IC pins and replaced , but it is not improved. I can not identify the problem IC. Character ROM may be suspicious, but this can not be inspected because it does not have.

Symptoms;

  • No texts, but colored squares are displayed at the position of letters.
  • 24 horizontal bars are displayed on the screen.
  • Keyboard inputs are not visible, but commands are accepted.
  • Can call GR mode, but not HGR/HGR2 mode.

 

I attached screen shot at startup. You can see the apple ii logo, the prompt and the cursor at the top of the screen. When I type something, a square appears instead of a letter.

I will be very thankful for getting advice on solving the problem.

 

 

 

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Image icon horizontal bars on the screen356.77 KB
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It is stuck in lo-res mode.

It is stuck in lo-res mode.

 

I'd recommend checking out a couple of the books on repairing Apples like you can find here:

 

https://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Books/

 

and here:

 

http://www.bombjack.org/apple/apple-books.htm

 

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check the ICs related to LO-RES mode

Hello, softwarejanitor, Thank you for your advice.

With reference to the book that you taught, I will check the ICs of the circuit related to LO-RES mode at the beginning.

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When I'm having almost any

When I'm having almost any issue with a II+, my first response is to reseat the chips. That seems to take care of 95% of the problems. Chip legs oxidize and lose good contact with the sockets.

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I reseated ICs in A and B rows

Hi, Wayne, thanks for your advice.

I reseated ICs in A and B rows today. With reference to “The Apple ii circuit description” and “Apple ii+/e troubleshooting & repair guide”, I carefully checked the ICs located on A3, A8, A9, A10, B4, B9, B10 and B11. And I also introduced an old 80 column card (I found it is working!), letters were displayed, so I concluded that there was no problem with Character Generator ROM.

But this time, since it is soldered to the motherboard, NE555 (B3) is excluded. As I wrote, there is no texts, but colored squares are displayed at the position of letters and 24 horizontal bars are displayed on the screen. When I enter commands from the keyboard, the colored square at the cursor position moves at the same time. Looking carefully, this square does not blink. I do not know whether the square flashes or the color changes in the current state, I do not know if NE 555 is directly related to this symptom, I will remove the NE555 to check if there is a problem with it.

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FYI -- Apple ][+ 80 column

FYI -- Apple ][+ 80 column cards have their own character generator ROM(s).

 

However, what it sounds like to me is if you are seeing colored blocks instead of text, your machine definitely sounds like  is stuck in low res graphics (GR) mode.  I don't think the NE555 is your problem.  It is likely one of the chips related to the soft switching between text and graphics mode.

 

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Start with checking the soft switch signals first.

Hi, SoftwareJanifer, thanks again.

I completely forgot that the 80 column card has own character ROM.

I read books carefully again and I understand I should start with checking the chip 9334(74LS259) located at F14 and the circuit in communication with this.

Start with checking the soft switch signals first.

Thank you.

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Solved | Horizontal bars on the Apple II+ screen

Thanks all! The problem has been resolved.

II checked the signal of 9334 (74LS259). The output is correct, but the signal level was unstable.
So I Replaced the capacitor near location F14. Now the symptoms have been resolved.
Since my Aplle II+ is an old machine, the electronic parts may be deteriorated?
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