Apple ii+ Stuck Screen Characters

13 posts / 0 new
Last post
Offline
Last seen: 3 months 3 days ago
Joined: Jun 26 2019 - 06:38
Posts: 7
Apple ii+ Stuck Screen Characters

I recently purchased an Apple ][ Plus system. I have wanted one for a long time and finally saw one for a a decent price, knowing it had some issues. In the listing the seller said he couldn’t get it to display a stable image on a screen at all.

 

When I received it was able to get a almost perfect image on the screen besides several $ symbols that seemed to be stuck where they were. Functionally I was able to write / run some BASIC programs and it seemed to work okay. A nice included item was a vision 80 column card which after reading the manual I was able to get working, while in 80 column mode there are no $ stuck and the machine seems to operate perfectly as far as I can tell. Waiting on a disk drive interface card to arrive to actually try to run some software. I tried removing both the language card and vision 80 card to see if the $ issue would go away , it did not.  I’ve read through the forum a bit about reseating every chip, started doing a few but no changes. Is there a repair manual available I should be looking at? Just want a good place to start. 

Offline
Last seen: 3 months 3 days ago
Joined: Jun 26 2019 - 06:38
Posts: 7
Image

Note this was taken when trying to use ADTPRO via audio cables, as you can see there was an issue loading ProDOS. Those character are stuck on any screen though.

Offline
Last seen: 3 months 3 days ago
Joined: Jun 26 2019 - 06:38
Posts: 7
96A2EBC2-F12B-4F06-92D7

Also note that when moving to a new line the letters trail up.

Offline
Last seen: 2 days 3 hours ago
Joined: Jul 5 2018 - 09:44
Posts: 354
Looks like bad RAM, probably

Looks like bad RAM, probably in the first bank.  There are a couple of service manuals which can be of use in diagnosing stuff like this.  I'll have to dig up the links.

 

 

Offline
Last seen: 3 months 3 days ago
Joined: Jun 26 2019 - 06:38
Posts: 7
Thanks softwarejanitor! I

Thanks softwarejanitor! I just tried to reseat/ clean up (the pins were a bit black, used some fine sand paper to clean them up) on the bottom row of RAM facing the keyboard, but nothing changed. Could be a bad stick, would the RAM from the language card work to swap out in that bank?

Offline
Last seen: 2 days 3 hours ago
Joined: Jul 5 2018 - 09:44
Posts: 354
It should, you can also swap

It should, you can also swap with the other banks and see if that changes the behavior.

 

Offline
Last seen: 2 days 3 hours ago
Joined: Jul 5 2018 - 09:44
Posts: 354
Also even swapping the chips

Also even swapping the chips around in the lower row may change the position or the incorrect characters.  If it does. that may be a clue that one of those chips has some stuck bits in it.

 

Offline
Last seen: 3 months 3 days ago
Joined: Jun 26 2019 - 06:38
Posts: 7
Great idea! That really

Great idea! That really helped me narrow it down, swapped 2 at a time, until I got a change and then swapped the last one I changed with another from the language card and no more stuck characters! Thank you very much. 

 

My next question is how conmon we’re these RAM chips from similar computer from same time period. I have a ton of commodore parts / computers etc ranging from the late 70s to the mid 80s that I was given. Do you think I would  be able to find a RAM stick that would be suitable ? 

Offline
Last seen: 2 days 3 hours ago
Joined: Jul 5 2018 - 09:44
Posts: 354
I'm not sure RAM chips from a

I'm not sure RAM chips from a Commodore will work.  The Apple ][+ used the common 4116 type DRAM chip.  You can buy new ones from places like JameCo, etc.

 

https://www.jameco.com/z/4116-15-Major-Brands-Dynamic-RAM-16Kx1-150ns-DIP-16_41339.html

 

 

Offline
Last seen: 3 months 3 days ago
Joined: Jun 26 2019 - 06:38
Posts: 7
Oh not bad wasn’t sure they

Oh not bad wasn’t sure they were still available new, I will have to pick some up! 

Offline
Last seen: 2 days 3 hours ago
Joined: Jul 5 2018 - 09:44
Posts: 354
Yeah, it isn't a bad idea to

Yeah, it isn't a bad idea to have a few spares.  RAM chips seem to be one of the most common failures on these old Apples.

 

Offline
Last seen: 3 months 3 days ago
Joined: Jun 26 2019 - 06:38
Posts: 7
Thanks again for your help, I

Thanks again for your help, I ordered 10 just to have some on hand for now. Waiting for my disk controller and then we’ll see if everything is working on that end. May be back with another post with more questions. 

Offline
Last seen: 2 days 3 hours ago
Joined: Jul 5 2018 - 09:44
Posts: 354
Glad I could help.  Hopefully

Glad I could help.  Hopefully your disk controller will work without issue but if it doesn't, I'm sure someone here can help out.

 

Log in or register to post comments