Re: Weird video on Apple IIc

[tomk@pro-nsdapple.cts.com (Tom Kelly)]

In <53m3fi$8vt@news.ycc.yale.edu>
macrl@pantheon.yale.edu (Ryan L Macarthur) writes:

>      I called 1-800-SOS-APPLE on this, and was referred back to Nathan 
>Mates's home page,"If you can't find the answer there, I don't know 
>where else you could," the tech support guy said when I told him it's  
>where I started from.  So perhaps he, or any of the Apple II faithful 
>could help me out here with telling me what's wrong with my //c.
>     I recently got my hands on an old Apple IIc [? PEEK(64447) ==> 255] and 
>it seems to have a couple of problems, the most disturbing of which is 
>the video display.  It's the normal "Apple //c" screen when the power's 
>turned on, but there are a couple of rapidly blinking @ symbols staying 
>in the same place on the screen.  After the disk drive reads the first 
>track or two on any disk I put in and crashes out (for example, the ProDOS 
>1.0.1 or "David-DOS" header will appear on the screen, and then the drive 
>starts screaming bloody murder... I'm thinking maybe it's the drive, 
>maybe it's another symptom of a deeper problem, I can't tell until I hook 
>up an external drive and try booting off that), the symbols are still there, 
>and when I hit CR the @ symbols start forming a column up the screen:
>
>               @
>               @
>        @      @
>        @     
>        @      @
>        @      *
>        @
>        *
>
>where the *'s are the rapidly flashing @ signs, and the ones that scroll 
>up the screen are normal.  Applesoft BASIC seems to work fine, and as the 
>screen is filled with text, text that is scrolled up past the flashing 
>@'s will be changed to a different character.
>
>"Sounds like some weird memory problem or something," 1800SOSAPPL Apple 
>II Tech Support Guy says.
>"So I guess the only solution is to try and get my hands on a new 
>motherboard or something," I says
>"Or buy a Mac," the Guy says
>
>    When I switch over to HGR, there are about a half a dozen pixels on 
>the screen which appear in the same place every time (as do the @'s), and 
>a little program written to draw 10 random lines on the screen, refresh, 
>and repeat works fine but doesn't in HGR2, but maybe I don't understand 
>Applesoft BASIC that well.  Lines will draw over the pixels on the screen 
>(which also blink a little) and will leave the pixels unaffected (a white 
>line over the pixel has a black spot on it, and the pixels will remain after 
>CLEAR).
>    When the keyboard is pulled off after power-up (it goes into 
>self-test otherwise), the problem is still there, which brings me to my 
>final question: what am I supposed to expect from the Apple //c self-test?
>
>Any insight would be whole-heartedly appreciated.
>
>-Ryan
>


The original IIc ROM does not do much of a self test.
If you upgrade the ROM, you can run the better self test.
I did this and found that I had bad RAM.
 
The original ROM is 128K
P/N        (342-0272-A)
Print Peek(64447) = 255
 
The upgraded ROM (UniDisk) is 256K
P/N        (342-0445)
Print Peek(64447) = 0
 
I have several  Apple IIc computers, some are already upgraded.
I have a EPROM programmer, so I copied the upgraded ROM into a EPROM.
Then I removed the original ROM from the socket and installed the EPROM
in its place.
 
Since the original ROM was 128K, but the upgraded ROM is 256K,
I had to "modify" the motherboard as noted below.
"bowtie" W1    (open)
"bowtie" W2    (shorted)
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