Apple II+ Corrupted Video

3 posts / 0 new
Last post
Offline
Last seen: 2 weeks 12 hours ago
Joined: Feb 19 2021 - 11:16
Posts: 1
Apple II+ Corrupted Video

Hi...

 

I have just become the owner of an Apple II+ out of Holland. Its in good physical condition except for what looks like a home built language card that is severely corroded. The language card was preventing even the motherboard from even powering up so I pulled it out. Then I got the power light but no beep. The video showed a screeen of mostly @ symbols and constantly rolled. Here is a snap:

 

Is this possibly due to a corrupt chargen?

Here is what that chip looks like (at least I think its the chargen). The EEPROM 's gold foil sticker has partially detached itself over the years. Could that have meant corruption from ambient light?

 

 

I lifted the SN74LS174N it is bodged into and the display displays "blocks" that look somewhat less corrupt. However, still now beep. BTW, the results are the same regardless of whether the keyboard is plugged in or not.

 

I appreciate any thoughts :-)

 

ElReli

 

 

 

Offline
Last seen: 1 day 16 hours ago
Joined: Jun 18 2010 - 13:54
Posts: 359
I doubt it's the chargen chip

I doubt it's the chargen chip. No beep means the CPU is not running and therefore the screen shows whatever random data is in the RAM.

That being said, it could be bad RAM, CPU, Reset, Clocks, etc. somewhat in that order. Need to pull out the logic probe or oscilloscope and the schematics to narrow it down. And of course, check the power supply voltages.

Offline
Last seen: 4 hours 16 min ago
Joined: Apr 26 2016 - 08:36
Posts: 98
jeffmazur wrote:I doubt it's
jeffmazur wrote:

I doubt it's the chargen chip. No beep means the CPU is not running and therefore the screen shows whatever random data is in the RAM.

That being said, it could be bad RAM, CPU, Reset, Clocks, etc. somewhat in that order. Need to pull out the logic probe or oscilloscope and the schematics to narrow it down. And of course, check the power supply voltages.

 You have video so the master clock is working.

 

Normally the thing to do is to remove all the cards, all the RAM except the lowest 16K and power up.  If you get the same screen then pull out all the ROM chips except the F8 Monitor ROM.  With that ROM chip in and no others the machine will power up, beep and give you the * monitor promt.

That eliminates upper RAM and the Applesoft ROMs as any cause (and makes troubleshooting easier).

 

If you still get the screen full of garbage then your F8 ROM isn't starting up - either because of bad RAM in the lower 16K, a bad f* ROM (unlikely) or a bad addressing chip somewhere on the board.  Consulting repair manuals like the ones here:

https://web.archive.org/web/20200224041310/http://www.apple2online.com/index.php?p=1_13_Apple-II-IIe

(the apple2online site seems to be down right now)

will help you move through possible scenarios.

Log in or register to post comments