Hello,I have an issue with my //e.It turns on fine, but there's always a grid pattern on the screen ,it doesn't seem to affect anything else though as it works fine, I cantexcute basic commands and programs, so it doesn't seem to affect the function.I don't know if it's a stuck bit in memory, or a video logic issue, but I've ran the self-test multiple times and it passes each time, so it seems there aren't any ram issues or other major issues.Could replacing the video rom work?Also, is there a way to properly reseat the existing video rom to resert it somehow? Would I need too boot the machine without the video rom, before putting it back in to reset something, is that possible?What other things could I try?
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It looks like there's an extra dot on the "space" character, as well as the "p" and "l" characters, but not "A", "e", or the square brackets.
Do the dots appear in low-res graphics mode (with the GR command in BASIC) or high-res graphics mode (the HGR command), or only in text mode (the TEXT command)?
If the dots do not appear in any of the graphics modes, it seems unlikely to be a problem with the video circuitry. Perhaps the character-generator ROM is decaying? Things you might do include:
I would expect corrosion to make *black* pixels in the output, rather than *white* pixels, though, so I'm still guessing ROM decay.
Thank you.I'm about to head ot bed, but I will try this tomorrow.I believe I tried the HGR mode before like a year ago, and the same thing happened, however I haven't tried GR yet.Yeah, I didn't do any cleaning when I originally got it in, so its dustry and dirty. I will check it.Hopefully it can eb fixed with reseating or cleaning, but I hope a new character rom if needed won't be too bad, I see a new video rom on ebay for about $25 Canadian, so hopefully its simialr prices.i'll report back after having done this tomorrow.Edit:ALso, this wasn't always an issue, it worked fine (just as it does now) without the grid dots, I bought a repalcement PSU for safety as to not use the original old PSU because its old and likely with bad caps and such, but the socket on the new PSU is so tight, that its hard to get the cable in, and it comes out easily, so a few times it came loose while it was on, I don't know if that might have done something or not. We'll see I guess.
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The Video ROM is the Character ROM. While it could still be bad, I'd also suspect the LS166 shift register at location F5, the LS374 Video Latch at D3, and possibly the IOU. If you still have any card in the AUX slot, I would remove that first. A scope would also be helpful in tracking down the issue.
Thanks.I've found the LS66 at F5 as its at the bottom beside the ram and the video rom.I've also found the IOU, luckily it's a socketed chip.I'm still trying to search for the LS374 video latch and D3.Unfortunately, I don't have a scope, so I can't just trace them, I may have to ask around, see if I can borrow one.I'll try everything else first, especially if they are just socketed chips that don't require soldering.Eddit: I found the latch, yeah it's a soldered chip as well.Alright, i'll tryu cleaning and reseatting the IOU as thats the only thing I can do now.if that doesn't work, i'll try to get a hold of a scope.Edit: and nope, cleaning and reseating the IOU didn't do anything.
This probablem wouldn't be caused by the LS166 at F5. The faulty pixels only appear at dots where the
VC,SEGA, andSEGBsignals are all high, but none of those signals can reach the LS166. For a similar reason, the LS374 isn't a plausible suspect. (There's no harm swapping the LS166 if you happen to have a spare, but don't bother mail-ordering one.)Although it's not likely, a card in the AUX slot could inject faults into the pixel stream because pin 27 (
ALTVID) connects directly to the pixel stream. So remove the 80-column card while you're doing any testing.Try this character-set testing program, pictured below. It puts all 256 characters on the text screen, arranged in a 16x16 grid so you can observe whether there's any apparent pattern to which characters are affected. Then it toggles between character sets each time you press a key.
Charset test.png
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Run the program and then press any key to toggle between the Apple //e's normal character set and its alternate character set.
Does the pattern of faulty pixels change each time you press a key? If so then the character generator ROM is at fault -- it's the only component that gets the alternate-character-set signal.
If this program pinpoints the character ROM as the cause, then there are several easy fixes you can choose from:
As usual there are many several times cheaper functionally equivalent alternatives to RM's, for example:
https://www.ebay.com/itm/315704578315
https://www.ebay.com/itm/315704578314
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Twiggy, aside from the image in the original post, how are you adding the images? They're super tiny and I can't make 'em larger (including open in new tab).
How is everyone else seeing detials?
I see no obvious way to make them bigger either. Would make it a lot easier to follow along.
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GOOD NEWS!It's fixed, all is good and normal now, no more dotted grid pattern!All it took was replacing the video rom, the one I ordered came in a couple days ago, and I got to it tonight.Glad it was that easy.
Interesting. Stuck bit on the ROM would have been the culprit. I suppose with age this is entirely possible.
Thanks for posting your followup.