Apple II clone - screen full of Apple characters on startup

[wottle]

Looking for some guidance as someone who was a Mac user as a kid, but not Apple II. I picked up an Apple II a few years back, and didn’t realize until after I bought it that it was actually a clone. When I first got it, I had issues with garbage on the video output and traced it down to what I believed to be memory issues.

I moved some memory around (fortunately every chip on the board is socketed) and got to a solid blank white screen on startup. I then took a known good CPU from a working IIe and put it in the machine and I was able to get to a startup screen that is just a solid block of Apple characters:



Anyone seen anything like this before. I couldn’t find anything like it in my googling.

ROM issues? Something because it’s a clone that will be hard tot track down? More memory issues?

Any help would be greatly appreciated!

 

[Arbee]

Without an oscilloscope or logic analyzer, this is gonna be pure guesswork. On 80s machines, common suspects are bad RAM (especially Micron-branded) and bad 74xx TTL chips (especially if Fujitsu branded). The ROM going bad isn't unheard of but it's fairly unlikely, especially if it's a mask ROM and not an EPROM with a window.

 

[wottle]

Without an oscilloscope or logic analyzer, this is gonna be pure guesswork. On 80s machines, common suspects are bad RAM (especially Micron-branded) and bad 74xx TTL chips (especially if Fujitsu branded). The ROM going bad isn't unheard of but it's fairly unlikely, especially if it's a mask ROM and not an EPROM with a window.

Interesting. I’ve never seen any other reports of this failure mode, so I was hoping it pointed to something. If there were still bad memory, I suspect I would see some corruption in the characters (I’ll try putting some of the questionable memory in to see how the machine responds).

Anyway, I don’t have an oscilloscope, but was hoping this seemingly unique failure would point to something more specific. I’ll keep trying to see what other components I can find replacements for and just do trial and error.

 

[Arbee]

The way the text mode works on the Apple II, bad memory won't corrupt the characters themselves, which come from the video ROM. RAM just determines which character is being drawn.

 

[wottle]

Wouldn’t corrupt RAM result in at least some of the Apple characters being drawn wrong?

If I’m understanding, the video ROM is likely OK because it’s drawing the Apple characters from it. This characters are loaded into RAM to be drawn, which means at least some of the RAM is ok.

But the fact it’s drawing a screen full of Apple characters could mean anything else on the board is bad and doesn’t point to anything in particular?

 

[stepleton]

I'm pretty sure the character bitmap isn't loaded into the RAM: the character stored in ROM (along with the lower bits of the current scanline) index into the ROM and the pixels go straight from there to the screen through the display hardware. So good-looking characters don't tell us much about the RAM, I'm afraid.

 

[bibilit]

Not easy to help without knowing exactly what clone you have. (Il or IIe ?)

Can you make some pictures of the board ? Some clones were pretty similar to the original while others were different.

 

[Arbee]

@stepleton is right, the character number is fetched from RAM, and that's used as a lookup to draw the character shape directly from the ROM. So the characters all being Apples means at least there are some bits stuck in the RAM, and nothing changing on the screen means the 6502 probably isn't running (possibly also because the RAM is bad).

@bibilit Because there are Apple characters (which were added as part of MouseText) it's an enhanced IIe or IIc clone.

 

[wottle]

Not easy to help without knowing exactly what clone you have. (Il or IIe ?)

Can you make some pictures of the board ? Some clones were pretty similar to the original while others were different.

Looks like it’s an official Apple board, or at least trying to look like one. I’ll try swapping all the RAM chips out for new ones and see if that helps.


One thing I did notice when I left it running a bit is that the middle chip labeled 8T97 gets very hot when running. It appears this machine had all 3 8T97 chips replaced with 74LS367 chips, which appear to be possible replacements for 8T97. I did confirm that no matter which chip I used in the 3 slots, the middle one was the one heating up. So is it getting too much power? Short elsewhere? Bad socket?

 

[mg.man]

Just a wild question... is the 6502 the right way 'round? Seems kinda odd it's oriented 'upside down' compared to the EPROM at the bottom...

 

[wottle]

Just a wild question... is the 6502 the right way 'round? Seems kinda odd it's oriented 'upside down' compared to the EPROM at the bottom...
View attachment 73574
View attachment 73575

Yeah, the CPU matches the silk screen on the board and the one that was in there when I got it.

 

[bibilit]

Yes, you have an original board there, not a clone.

The PSU should also be the original one, on clone units the connector was not this one.

Concerning 74LS367, yes correct part, still available.

The Apple II only needs the first ram row to work, si you can try removing the second one and swap chips.

 

[mg.man]

Yeah, the CPU matches the silk screen on the board and the one that was in there when I got it.

Umm... but it's not working, and hasn't right? I found another Rev 7 Apple II board, and its CPU is rotated 180° :

 

[wottle]

Yes, you have an original board there, not a clone.

The PSU should also be the original one, on clone units the connector was not this one.

Concerning 74LS367, yes correct part, still available.

The Apple II only needs the first ram row to work, si you can try removing the second one and swap chips.

Yeah. I've tried several combinations of multiple rows, only the first row, old RAM, new RAM, etc. Unfortunately I just get varying degrees of either white screen with garbage, all Apple Logos, apple logos with some garbled characters. Another odd thing is I've had times where the RAM chips in one config will work, but then I'll remove and reseat the CPU and the screen will change from having all Apple characters to white screen with garbled artifacts. This machine may be beyond my abilities to diagnose and repair.

I also tried my power supply from my working IIe and it did not change things.

As for the clone, it appears I have a clone case that had an original board in it. The keyboard has a numpad on it, and the main keyboard keys have commands on the front of them. It doesn't have an Apple (command?) key, which made me think it was more likely an Apple II vs a IIe. The power supply is a Peak Power KHP 4007. The original owner had replaced at least a couple of the RAM chips, as the three tows did not match and the second row also had two chips that didn't match.

 

[wottle]

Umm... but it's not working, and hasn't right? I found another Rev 7 Apple II board, and its CPU is rotated 180° :

Looks like I have a Rev7 board that has a different orientation, like this one: https://www.reactivemicro.com/product/apple-ii-plus-rev-7-rfi-motherboard/ and here: http://appleclub.pl/wp-content/uploads/2018/04/IMG_0619-1.jpg

Or the CPU in your image is actually installed backwards. Just to check, I did try the "non-working" CPU with the orientation set to the way it is in your picture and it did not work. I got a blank white screen.

 

[bibilit]

Keyboard is not original, probably a clone.
No Apple II had a numeric keypad, only the platinum had one.

 

[mg.man]

Looks like I have a Rev7 board that has a different orientation

How totally confusing! The second pic you linked does show "dots" near the chip corners which likely indicates PIN 1 position:

These do appear to coincide with your board, so I guess you're all good. Still... annoyingly confusing!

 

[Arbee]

Ok, that's weird. An Apple II/II Plus shouldn't have MouseText character ROMs.

 

[bibilit]

Well, the original manual for the Apple II is showing also the 6502 upside-down.

Concerning the characters, the label on that Rom can be a clue that an upgrade has been done.

 

[wottle]

Ok, that's weird. An Apple II/II Plus shouldn't have MouseText character ROMs.

I should also consider the possibility that the person who owned this before me did some messing around and possibly tried to do some modifications that left it in this non-working state. I got it from an elderly woman who said it was used by her husband many years ago.