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Apple //c RAM Problems

I guess Apple quit caring about the quality of their Apple II RAM for a while.

The fact that you had similar problems when your RAM was bad reassures me a bit that (with help from this forum) I can get my system running.


I wasn't able to replace chip F-14 this Friday, but I hope to replace it today.

I'll get back with the results ASAP.
 
OK, I just replaced chip F-14, and here are the results:

  • All garbage characters are gone in 40-column mode! :D
  • However, floppy disks will not load...
  • The ROM Diagnostic check returns "RAM 00010000."
  • 80-column mode has (, @ and ` garbage characters.

Any ideas?
 
Well, ROM Diagnostic is now claiming bit 4 (MRD4 RAM) is bad.
80 column text garbage may indicate that Auxiliary RAM bank also have multiple failures.
The way Main/Aux RAM is mapped to 80 column is such that Aux RAM occupies the odd number columns (start counting from 1)
So if the garbage characters are in odd columns, Aux RAM chips need replacement. If they're on even columns (main RAM bank,) you got bigger problems than just RAM.
SPC = 0x20, ( = 0x28, @ = 0x40, ` = 0x60. So bit 3, bit 5 and bit 6 are bad. If these garbage occupies ODD columns, you need to replace ARD3, ARD5 and ARD6. If they're occupying even columns, you might be better off to look for a new machine.
 
Thank you dorkbert.

As I've stated before, I don't have the machine with me right now.

When I tested earlier today, the garbage characters were spaced out on the screen in what seemed to be the odd columns.

I'll try replacing the chips you specified tomorrow.

Thanks,

WMH
 
I know what you mean. :D

I'm sure there has to be at least a couple of good RAM chips on the board somewhere.

One quick question:

What is the main RAM bank, and why does it cause problems bigger than RAM?
 
You've been replacing RAM in the main bank, and if after you've replaced ALL of them with known good parts, but you're still getting artifacts on screen, something OTHER than RAM is failing, and it might be easier to chuck the whole unit and get a replacement.
 
Just replaced MRD4.

Results: Total System Failure

The screen filled with random text and then nothing happened (except the speaker was crackling.)

When I press control-reset, the random text changes.

I tried to boot without a keyboard with the same results, except that instead of text there are random blocks.

What should I do???
 
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It seems pretty bad for just RAM.

Are the RAM chips accessed sequentially?

If they are, then it would make since because it couldn't have used all of the RAM before.

I did have a problem where I exceeded the good RAM "capacity" and the screen filled with similar gibberish when I tried to enter a line of code in AppleSoft BASIC.

But that gibberish went away on a system reboot...
 
I don't know.

My friend helped me solder this chip, but he didn't do the best job.

Could this or a faulty new chip cause these problems?

I'm really starting to think that something else is totally ruined.
 
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Here's the lastest update (I guess it's good news.)

I removed the new chip, and found that one of the wires that goes under the RAM chip (attached to the board originally) was snapped.

So here's what I'm going to do:

I going to put in a new chip, and try attaching the wire either to the bottom of the pin or to the side of the pin.

I'm guessing that a snapped wire would cause a short until it was reattached.

What do you think?
 
Yeah, I'm asking someone to help now.

Is there any hope that resoldering the snapped wire can fix the system or should I start checking eBay?
 
WMH said:
Is there any hope that resoldering the snapped wire can fix the system or should I start checking eBay?
Click to expand...
Yeah, you can fix that easy. Sounds like you lifted one of the traces. Find where it connects to, and solder in some 30 gauge wire wrapping wire (or similar) to replace it. It happens, and it's easily repaired. Check to make sure you didn't pull out a feedthrough at the chip - the little ring that connects through the board. Might have to patch around that too, depending on what broke.

-Ian
 
OK, thanks. (I can breathe a sigh of relief now!)

I'll give it a shot tommorow.
 
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