Apple II+ 48k 6502 and/or rom issue

Sounds more like a ROM issue. If you have a ROM card (or Language Card) you could use that to substitute for the motherboard ROM to prove that. Or download a binary image of the E8 ROM and compare it to yours.  There are also many diagnostic disks that you can run that test the ROM.  

Replacing the ROM would require finding an oem ROM or using an EPROM with adapter. There's also the ROMX which we sell through ReActiveMicro.com. 

I agree that it sounds more like ROM.  If it was the 6502 it seems like it would affect a lot more than just graphics.

Testing the ROM and/or comparing to a known good image is a good start.

Do bootable assembly language-written disks run properly?  Like games, for instance?

Something that runs in machine code and bypasses ROM but requires most of the RAM?

That would go a long way to figuring out if ROM or RAM is the culprit.  

Have you tried running any diagnostics like APTEST or Apple Cillin? 

Your post says you have no expansion cards...you can still load software (games) via the cassette ports and a smartphone through the website http://asciiexpress.net/gameserver/

Do a CALL -151 (which, even if it breaks, will get you into the monitor, heh), followed by EC40L, and compare the first few lines of output with the following:

]CALL-151

*EC40L

EC40-   85 9E       STA   $9E
EC42-   85 9F       STA   $9F
EC44-   85 A0       STA   $A0
EC46-   85 A1       STA   $A1
EC48-   A8          TAY
EC49-   60          RTS

If it doesn't match that (looks to me like EC44 is liable to be a 00/BRK), then your ROM is bad.

LennyStudios wrote:

Thanks - I tried this and you were right, $EC44 was a brk and a few others didn't match as well

if I'm going to replace the rom chip is there a good way or place to get it? It seems to be relatively cheap but not as easy to find.

Finding an OEM replacement for a single ROM is going to be hard. Many sell EPROM substitutes but that requires an adapter socket. You might be better off replacing ALL of the ROMs with one of the ROM boards such as the MultiROM or ROMX (which I helped design and is available for under $50).

In post #8, 'LennyStudios' wrote:

" While I still want to look into other solutions as well and do some reaserch (ideally I can find a replacement for just that chip but as you said it would be difficult), but ROMX looks fairly simple to implement and much easier to get. "

Uncle Bernie says:

All ROMs in any Apple II have almost a standard 27XX EPROM footprint, with the exception of a few pins which are mask programmable chip selects. Early Apple II had 2kByte ROMs, which could be replaced by 2716 EPROM, but you could also use 2732 EPROMs, which are easier to get.  You need an EPROM programmer to program them. The ROM images can be found on Asimov.

The only 'hardware' challenge is to replace the up to three mask programmable chip selects on the ROMs with a TTL address decoder. This could be done with a single 74LS138 piggybacked on some other TTL. You would bend up the pins on the EPROM which sit in the three programmable chip select locations and wire them to the appropriate decoder outputs.

Even easier would be to pull the whole upper 8kBytes of ROMs and put a type 2764 EPROM in one of the sockets. The four upper pins of the 2764 would hang in the air, but they still can be flight wired as needed. Providing a suitable chip select for this sole EPROM would be less effort.

But all of this requires -

a) some fairly low level understanding of digital electronics (what are EPROMs ? What are chip selects ? What is an address decoder ?)

b) an Apple II schematic

c) proper tools (soldering iron , EPROM programmer, if EPROM not blank, an EPROM eraser, too)

d) some thinking on how to wire everything up

No everybody has these tools or skills. But I would repair an Apple with bad ROMs using EPROMs, as I have all the tools and skills.

However, before shelling out money on anything, try if pulling the ROM from the socket and putting it back helps. Some ROMs I saw in Apple had badly tarnished pins, and the sockets used by Apple at the time being were cheap crap, too. So maybe it's just a contact problem. Which you should rule out before spending money.

- Uncle Bernie

As usual Uncle Bernie brings up a good point.  Bad contacts due to dirty or corroded chip pins and/or sockets could cause a ROM to appear bad.  Also what he says about sockets failing is also true.   It would be unfortunate to do all the work to get another ROM or an EPROM substitute and then find out the original chip is OK but the socket needs to be replaced.

In my case I have multiple ][+ machines so I could try a different and known good ROM chip of the same programming  in that socket and see if the machines runs correctly.  However I suspect you don't have an extra one to try...  But you do have the other ROMs.  While you won't read the correct data for the location you are looking at, if you swap one of the other ROMs into that socket it should display the correct data for the other location.  You just need to know what data to expect, but you can check that from the monitor before you swap the chip over.

I hope that all makes sense...  it's a little bit of an unuaul suggestion I guess.  But it should work to test to rule out the socket being bad.