Apple II RAM issue ?

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Apple II RAM issue ?

Hello Community, 

I was struggling to make a language card working and I have been investigating like hell including changing the SRAM chip with older one... A complete disaster. 

The language card was actually working and the fault is coming from the Apple II 

I have run the Memory Dead Test ROM from MisterBlack (Adrian). And my issue is coming from the RAM circuitery. 

The result of the RAM test is : 

It means that I have error on D2 and D5 correcponding to chip on C5,D5,E5 and C7,D7,E7. 

Of course I have fully tested and also replaced the 4116 RAM IC but with no luck. 

I have the feeling that the RAM MUX is faulty but it is not the case 

 

How should I investigate ? What would be the cause ? 

Thanks for your support and your help

Vincent 

 

 

 

 

 

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You mean DRAM? I have no idea

You mean DRAM? I have no idea what Adrian's tester is showing, was that a defined write (maybe $00) and reading back $20? or is that saying bit 5 is always wrong? I don't know....

Given I don't know what I'm looking at and it looks like the problem is consistent in every page but $00 (although that's ood maybe it's not really tested given it's use?)

I'd look at the 74174s in row B and the chips to their left or right, it's a double set of 2 chips for each nibble of the byte. If course you should never test RAM (DRAM) like this, you should start with only one row (16K and if a II configure memory selects).As a row tests good move to two, then three then add the RAM card. Slow and simple, is easiest path to "good". If Adrian's ROM supports just testing 16, 32, 48 and 64K but I don't know cuz I don't use it). I just use the monitor to test RAM. And test from 265->3FFF (7FFF or BFFF as I build out).

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jeff d wrote:...I have no
jeff d wrote:

...I have no idea what Adrian's tester is showing, was that a defined write (maybe $00) and reading back $20? or is that saying bit 5 is always wrong? I don't know....

Given I don't know what I'm looking at and it looks like the problem is consistent in every page but $00 (although that's ood maybe it's not really tested given it's use?)

...

 

It's perhaps the best tool out there for anyone who owns an EPROM programmer and he has described how it works very clearlyhttps://github.com/misterblack1/appleII_deadtest

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Vibr,
Vibr, Page line at top 4_ is first 4 bits of the upper 8 bits of address, the left had side has the lower 4 bits of the upper 8 bits of the address. So odd pages of 256 bytes are reporting error at 41XX, 43XX .. 4FXX, 61XX, 63XX .. 6FXX 20 represents bit 5 is set, which corresponds for memory 4000-7FFF to be RAM at location D8. Try swapping the two RAM chips with each other at locations D8 and D7. If the error with the test changes from 20 to 10 then the RAM you just moved to location D7 is faulty.
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Bingo, thank you D8 was bad.

Bingo, thank you D8 was bad. this is a bit crazy because I have tested with an external tester all the  DRAM IC and noone was marked bad. using the MisterBlack DEAD TEST I had one error. 

Now it is fixed, thanks guy for your helpVincent

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VIBR wrote:Bingo, thank you
VIBR wrote:

Bingo, thank you D8 was bad. this is a bit crazy because I have tested with an external tester all the  DRAM IC and noone was marked bad. using the MisterBlack DEAD TEST I had one error. 

Now it is fixed, thanks guy for your helpVincent

Many cheap offline RAM testers don't test RAM properly.  Most of them write a "1" and then read it back, then write a "0" and read it back and call it good if they read the expected result.  But most don't do other extensive tests like 0-to-1 transitions, 1-to-0 transitions, all 1s, all 0s, and any number of permutations that could cause RAM to return a fault.

 

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