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Trouble tracking down bad RAM in a Lisa 2/5

redruM69

Active member
I recently acquired a Lisa 2/5 as a project.  PSU fixed, corrosion repaired.  It has 2x 512K RAM cards in it.
Getting an error 70.  I have narrowed it down to 1 card.  The bad card is in slot MEM 1, MEM 2 left empty.
Enter service mode, Read memory location $186 gives 0000 0000 0000 0004.  Cool!  From what I read, that means the chip at Row E, Column 20 is bad. 
Replaced the HM4864P-2 with a now socketed Fairchild MB8264-20, which I believe to be compatible.
Still get error 70!
Memory location $186 now gives 0000 0000 0000 0404
So it appears that not only did the RAM I replace still not work, but now i have a new bad bit on column 3 row E?

Thoughts?
 

 

redruM69

Active member
Update: RESOLVED!

I made an error/typo with my original assessment.  It was column 3 the entire time.  I wrote down the wrong value. :x  
This means I accidently replaced the wrong chip!  It also appears the MB8264-20 is NOT compatible.  I stuck in an NEC D4164D instead, and it worked fine. 
Replaced column 3 row E with another D4164D, and no more errors!
 

Now to move onto the floppy drive not working!

DSC_0633.JPG

 

MOS8_030

Well-known member
Update: RESOLVED!
 

Now to move onto the floppy drive not working!
Congrats!

Good luck with the floppy drive. I gave up on mine. Even with a different drive I still had issues. I think maybe the Lisa Lite card has a problem.

 

redruM69

Active member
I haven't looked at it close yet, but its not auto-injecting.  I noticed one of the sensor LED's inside is glowing, so it is receiving power at very least.
What were your symptoms?

 
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