Apple III without any text

Hi Bengt,

a 342-0060 ROM would be OK to be used in G9. My Apple III has a 341-0060 in G9 - even though the mainboard/schematic says 341-0030. This ROM mainly controls timing signals. Not sure, but it might differ dependening on 50Hz/60Hz (European/PAL vs US/NTSC), since the wiki explicitly mentions "50Hz" for the -0060 variant. Your 342-0060 is probably just a newer version of the 341-0060. Is yours a PAL or NTSC machine?

I haven't checked with the Apple II schematic, but I'd really be surprised if any Apple II ROM could be used to replace this particular ROM. The Apple II's video logic is quite different. And the G9 ROM is not a simple character ROM, but a device generating several complex logic signals. In fact, the Apple III does not have a character ROM, like the Apple II. Instead, it uses a RAM - so the character generator is fully programmable.

Your issue certainly looks like an issue with character generation. It could be a logic issue with reading/generating the characters. But it's also possible that there's an issue with CPU being unable to write to the character RAM. The CPU needs to program the character RAM at start-up (copy the character set from the boot ROM). When that somehow doesn't work, then the character RAM has no useful content.

Have you tried following the fault tree diagnostics in the Apple III service manual? I found this very helpful when I fixed my Apple III.

cheers,

T.

[quote=macbengt]

Hi Applefritter, this is my first thread in this fine forum.

I have an Apple III bought on ebay. It was sold as defect, it was dead on arrival. Model  A3S1 no 57901  motherboard  820-0043-00E  5V memory board, american keyboard. The power supply was dead. Defect KB lamp. A defect trace on the MB so no voltage to the KB. After replacing with a new PSU, new KB lamp and repair of the Mb the Apple III is partially working.

There is a videoproblem, there are vertical lines on the display. Sound is ok . Floppy drive is OK. There is no text.

20191117_221320b.jpg

Reset key is working. When I test  Ctrl-OpenApple-Reset key sequence its probably starting in monitor mode. But no text

20200107_050634b.jpg

After reparing the AIII  it is booting ( Apple III system utilities) and the keyboard is working, but no text .

t

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.

 I have reseated all IC, replaced the RAM on the 5V memory board with new RAMs but the same result.

According to Apple III service reference manual ( p 13.53) it can be defects in several IC on the motherboard. I have replaced the two 2114, switch positions of all LS374 and LS161 without any change.

The ROMs on the MB are not exactly the same number that’s printed on the MB. According to  https://kb.pocnet.net/wiki/Apple_Chip-Bezeichnungen    the ROMs installed on the MB have the same function except position G9 . The MB is marked with 341-0030 on G9, (Video elements/attributes generator) but the installed ROM is 342-0060. It looks like a EPROM ( D2716) with a label saying 342-0060. Not original Apple.

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There are a lot of threads about Apple ii character generator in this forum .

https://www.applefritter.com/content/vertical-lines-boot

https://www.applefritter.com/content/text-not-appearing-correctly-apple-iie

https://www.applefritter.com/content/apple-iie-issue-weird-chars-etc

Also about 2114 static RAM in A3

http://www.vcfed.org/forum/archive/index.php/t-34430.html

https://www.applefritter.com/content/apple-display-problem

My question is if the G9 ROM  is the problem. I have not found any information about 342-0060. I have read someware that its posible to try with ROMs from Apple IIE in Apple III .  I have a working A IIE but I have not tried that. Is it better to  burn a new EPROM 341-0030 from a ROM image?

Thanks for any help.

/Bengt

[/quote]

That looks like a 2716 EPROM.  You could pull it, put it in a programmer and see if it has anything in it.  The image is probably available online.  You should be able to procure a new 2716 and burn it with the correct image as you say.   I have a MiniPro TL866CS programmer which isn't terribly expensive and I've burned quite a few 2716 with it.

If you have a look at the first page of the schematics, it has a note relating to the euro verion using the 341-0060 version of the rom. See here:

https://www.apple3.org/Documents/Schematics/Main%20Logic%20Boards%202-1.jpg

I expect your Apple/// is one made in Ireland from the serial number, so probably came from the factory setup with this eprom. Maybe you can comfirm this from the serial number sticker. It would be great if you could have it read by an eprom programmer as I don't belive there is a copy of this rom dumped and available anywhere online. I don't think this would be the cause of your issue as this would be just timing related for the video signal, and that seems to be working ok for you.

As you have tried replacing the 2114 and associated latches, then maybe the circuitry to enable the character rams when writing the character data into them is not working. you could try replacing the 74LS20 in B10, and maybe working back from there. See in the top left of the video circuit:

https://www.apple3.org/Documents/Schematics/Video%20Logic.jpg

/Rob

Just thinking about this one a bit more, it might be good to see if the graphics modes display ok or not. If you try this diagnostics disk, and hit enter the first lot of tests is for video. Then hit spacebar to move through the screens. you shoud see a picture on the screen for some of them.

https://www.apple3.org/Software/system/Apple3Diagnostics.dsk

/Rob

Thats really great to hear, good your getting closer to having it all working 100%.

/Rob