Apple II europlus memory problems

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Apple II europlus memory problems

Folks, having fixed my machine by replacing row C with new memory chips I decided to try and figure out which chips out of all of the onces I extracted were bad. I have done this by dropping a selection of the previously extracted chips into row D and then running a memory test. The test fails as soon as it hits 16,384 (row C only) and the chips in row D start to get very hot. Tried different chips, same problem, same heat. I therefore raided my dwindling stock of new memory chips and dropped them into row D and the test ran perfectly to 32k (row C and D) and the heat problem disapeared in row D. I now need to sort row E, which had the same problem with old chips.

My question is, could all of the old memory chips be defective through some sort of catastrophic memory chip killing problem or could one or two bad chips cause a whole row of chips to heat up and fail the test (I thought the test would run until it hit the defective chip).

Would I be best to do a chip by chip test amongst good chips and if so would the constant swapping weaken the chip socket? I am not too precious about the old chips, just a little reticent to junk 32 chips (inc the 16k card which came in the machine) unless I have too.

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Re: Apple II europlus memory problems

Atomtan,

In your case, I think the better solution is to swap one by one the good chips with the presumed bad ones and make a RAM test after every swapping.
I have used this method a couple of time. The sockets aren't too fragile, but the pins of the chips are !

But it could be dangerous : perhaps a single defective chip could destroy the others...

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Re: Apple II europlus memory problems

My memory testing may have an issue. I have been using Mike Willegal's site for reference and used this BASIC code from that site to test memory. My issue is that when I ran this on my fully working benchmark machine, this code fails its poke command at address 32,768 even though I can peek addresses above that. Strangely, the second machine I am restoring fails at the same point. To be honest, I have not yet read all of the on-line manuals to see if there are any other memory tests to check I have the full 48k running. Any suggestions?

Also, I am struggling to find many 4116's or MM5290m's to replace defective chips in Europe. Does anyone have any good sources?

Many thanks

10 PRINT “WRITING MEMORY”

20 FOR I = 6000 TO 49151

30 I%= I

40 J%=I/256

50 POKE I%,J%

60 NEXT I

70 PRINT “CHECKING MEMORY”

80 FOR I = 6000 to 49151

90 I%=I

100 J%=I/256

110 IF PEEK (I%) = J% THEN GOTO 140

120 PRINT “ERROR AT ADD:”;I%;” DATA:”;PEEK(I%);” EXPECTED:”;J%

130 GOTO 160

140 NEXT I

150 PRINT “NO ERROR”

160 END

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Re: Apple II europlus memory problems

Have you tried the memory test here:

http://www.applefritter.com/content/apple-ii-bad-memoryrom
1. Go to the monitor (CALL -151)
2. Type in the following code (don't forget the space between 34:14 and Return).
C050 C053 C054 C057 N 265:FF N 266<265.BFFEM 266<265.BFFEV 265:0 N 266<265.BFFEM 266<265.BFFEV 34:14 (don't forget the space and... Return)

Or Mike Willegal's, here:
http://www.willegal.net/appleii/6502mem.htm

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Re: Apple II europlus memory problems

This test worked on both my benchmark machine, and the the machine I am repairing (sorry for not digging through the old threads enough). I used chips from an Apple 16k card which came with the machine in row E so from reading the narrative of the thread I assume both machines have passed the 48k test and I can assume the 8 chips from the apple card were good. I am really pleased with that.

I have left the repaired machine cycling this test over and over to make sure the RAM does not overheart, and then its time to clean up the keyboard and contemplate testing the old RAM chips.

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Re: Apple II europlus memory problems

Old thread, but anyhow... Atomtan, the reason your original program failed at 32K was because I% is an integer variable. The maximum value for integer vars is 32K.

At a minimum, I would also change the code around line 110 and 120 to only peek() once.

Cheers,
Michael.

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