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Apple III restorationr - Video problem

N

NickM

Member
Joined
Nov 19, 2012
Messages
10
Location
Brisbane, Australia
I've been restoring my Apple III (non plus model). I've got the floppy drive lubed and cleaned up, repaired the keyboard (contacts) and have the system now booting up fine... except for 1 "minor" video glitch.

When displaying text mode, the screen is full of vertical lines spaced 1 character apart from the top of the screen to the bottom. Text is still being displayed normally behind this and the system operates normally. It does this for both 40 and 80 column mode.

But, this problem does not happen in graphics mode. Screen is perfect. Only when in a text mode.

I've been swapping chips, reseating chips, replaced entire 128K RAM still no change.

PB190209.jpgPB190208.jpgPB190210.jpg

Like I said, only text mode. Perfect in graphics.

Anyone familiar with the Apple II hardware enough to give me a few pointers of where to look next?
 
dorkbert said:
looks like character ROM problem, since your graphics mode looked clean.
Click to expand...
Well, yes and no - fonts are downloadable. The trek-like font on the graphics screen is one example. On the BASIC disk, there's a font demo program "FONTDEMO" - it continuously loads and displays fonts. It would be interesting to know how that behaves.

I'd have pegged memory (specifically video memory) since it looks like one bit is stuck on.
 
david__schmidt said:
Well, yes and no - fonts are downloadable. The trek-like font on the graphics screen is one example. On the BASIC disk, there's a font demo program "FONTDEMO" - it continuously loads and displays fonts. It would be interesting to know how that behaves.

I'd have pegged memory (specifically video memory) since it looks like one bit is stuck on.
Click to expand...
I am thinking the default character ROM is bad. He can always download font into RAM and see if text mode is still messed up.
 
He sees vertical bars on boot; the RETRY comes from ROM. That would implicate either the chargen ROM or RAM. Then SOS boots, and downloads a new font (the one you'd see in Business BASIC, for example) which also has vertical bars. So it's either both ROM and RAM, or just RAM...
 
david__schmidt said:
He sees vertical bars on boot; the RETRY comes from ROM. That would implicate either the chargen ROM or RAM. Then SOS boots, and downloads a new font (the one you'd see in Business BASIC, for example) which also has vertical bars. So it's either both ROM and RAM, or just RAM...
Click to expand...

you're right, RAM is the most likely suspect.
 
The Apple III doesn't have a character ROM as such. My understanding is that it downloads the character set from the boot ROM at startup to a separate RAM space outside of the 128K/256K dynamic RAM into a 1024 byte static RAM space that is composed of 2 x 2114 memory chips.

To test for a stuck bit, I swapped these 2 RAMS over to see if the lines moved but no change. I'm looking through my parts spares for replacement 2114's to further confirm if my original RAMS are ok.

To check main RAM, I replaced all the 32 dynamic RAMS with another set but the problem remained.

I've set up my CRO (a crappy 6Mhz model) and I plan to backtrack the video signal from the output, working my way back through the circuit to see where the source of these lines is coming from.

Stay posted!! :)
 
david__schmidt said:
Do you see the lines "paint," or do they appear the moment the power is applied?
Click to expand...

No "paint". They appear instantly.

An observation that may help in narrowing the problem... When an inverse character appears on the screen, that part of the vertical line is also inverted so the vertical line still appears through the character. In other words, the lines are not just a lit-only lines, the inverse video function of the characters seems to be still working.

Also, color (green scale on monochrome) seems to be working so it's not in the color generating portion.

It all seems to be right at the character creation part of the logic.

The vertical line seems to be midway within the character (eg. it's sitting right on the vertical line part of a "4" character).

Will be borrowing my friends Apple 3 plus soon so I can trial a few chip swaps between machines.

Nick
 
NickM said:
No "paint". They appear instantly.

An observation that may help in narrowing the problem... When an inverse character appears on the screen, that part of the vertical line is also inverted so the vertical line still appears through the character. In other words, the lines are not just a lit-only lines, the inverse video function of the characters seems to be still working.
Click to expand...
Wow, so it sounds like some reversed logic rather than stuck bits.

Have you reseated all the chips?

What does the fontdemo program do?
 
Yes, all chips reseated. Don't have the fontdemo program but the demo disk that comes with the III had stripes on the text pages, no stripes on the graphics pie and bar charts pages and stripes again on the running horses downloaded characters animation demo.

Have a III+ now so hope to do chip swaps tonight and hopefully find a dud chip somewhere.
 
FIXED!!!!

Pretty well got it to work on my first chip swap from the Plus.

The problem was indeed one of the 2114 static rams that hold the loaded character set.

Luckily, I managed to find a pair of replacements in my parts box and I can now announce that the world has one more operating Apple III!!

(It's like saving an endangered species!)

Now all that's left is to find a cheap Profile controller card and get my Profile hard disk running too.

Thanks for everyone's help.
 
The final chapter of my Apple III restoration...

I hit my Apple III case with the "retrobrite" technique to remove the yellowing from the case.

It now looks almost like new!!

The only thing left is to replace the worn Apple III badges. The paint has deterioted badly with the lettering having lost all silver/chrome coloring.

Does anyone have or know where I can find replacement badges for the Apple III (not plus model)? I need bot the "Apple" badge and the "III" badge.

Nick
 
NickM said:
The final chapter of my Apple III restoration...

I hit my Apple III case with the "retrobrite" technique to remove the yellowing from the case.

It now looks almost like new!!

The only thing left is to replace the worn Apple III badges. The paint has deterioted badly with the lettering having lost all silver/chrome coloring.

Does anyone have or know where I can find replacement badges for the Apple III (not plus model)? I need bot the "Apple" badge and the "III" badge.

Nick
Click to expand...

John Woodall currently has the "///" badges. Sometimes he has some "Apple" ones as well, but not at the moment. He's not exactly cheap, though.

http://vintagemicros.com/catalog/index.php/cPath/29?osCsid=024fe1b1464106211f99e07a6a833fcf

- MM
 
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