Reconstructing an auctioned Lisa

[berskyboy]

Yours is part number 341-0348, which is for Macintosh XL computers that boot only Mac OS. If you want to boot LOS, you'll need to remove that PROM and replace it with 371-0072, and disconnect the transformer between the Lisa's Video Board and the CRT - thereby enabling Lisa Office System's native resolution.

This is what shows up in Mac XL with the black borders on each side, and when I put the CRT P1 and P2 it went directly into the Lisa Video Card, so maybe it's still stock CRT?

https://www.dropbox.com/scl/fi/bour2rbj1jygmhpvmg7fd/IMG_4174.jpeg?rlkey=ecybjape2jj2gg65qdu3mzf0l&st=2fpr9klf&dl=0

[berskyboy]

There is an adapter design to use an EPROM in lieu of the one-time-programmable 20 pin bipolar PROM, but I've not tried it.

Note that the Video PROM contains the Lisa's Serial Number, so there are numerous variants of the programmed contents of this part (containing different serial numbers).

I believe you are in Canada with me, so I may be able to provide these; contact me privately to discuss.

sure thing, I did drop you an Message.

[TorZidan]

I tried the Piggyback method still getting
00000186 0000 8000 0000 0000 0000 0000 0000 0000

00000186  0000 8000 0000 0000 0000 0000 0000 0000
https://www.dropbox.com/scl/fi/kvfsgapov3rf3fizzh8ik/IMG_4151.jpeg?rlkey=ke4waclbeexuouu5rm4jqhzee&st=e0t9slf7&dl=0

every time I ask AI to tell which chip it says different chips.  Is there a lookup document? 
I tried this website but it's down

https://lisafaq.sunder.net/single.html#lisafaq-hw-mem_error

Here is a copy/paste from my records:

Each memory board has 4 banks (of 16 chips each), named "A,B,C,D".
Each "word" (4-digits in your post) corresponds to a memory board + "bank".
Look above for banks that show non-0000: they have faulty ram chip(s).
If there is one memory board in slot MEM 1, then the 8 words are for the following banks:
  B C D E  x x x x          (x means "unused")
If there is one memory board in slot MEM 2, then the 8 words are for the following banks:
  E D C B  x x x x
If there are two memory boards installed, then the 8 words are for the following banks:
  MEM 2    MEM 1
  E D C B  B C D E

Now that we determined the board and bank(s) that have bad ram chipss, we need to determine the ram chip column number in each bank:
Word  Bit#= Column Number
  0001  0  =  22
  0002  1  =  21
  0004  2  =  20
  0008  3  =  19
  0010  4  =  18
  0020  5  =  17
  0040  6  =  16
  0080  7  =  15
  0100  8  =  1
  0200  9  =  2
  0400  10  =  3
  0800  11  =  4
  1000  12  =  5
  2000  13  =  6
  4000  14  =  7
  8000  15  =  8
If there is more than one bad chip in a given bank, there will be more than one bit set and you'd get a word different that the ones above.
In this case, proceed to identifying the bad chip similarly to how it's done  on a Macintosh 128k.


So let's assume you have one RAM board in slot MEM1 (verify this!!!). The error is 8000 in Bank C on the board, which is the ram chip in column 8. So pull tooth C8.

[berskyboy]

So let's assume you have one RAM board in slot MEM1 (verify this!!!). The error is 8000 in Bank C on the board, which is the ram chip in column 8. So pull tooth C8.

I put in piggy back chips in C8 and D8 (both one at a time and together)

got
00000186 0000 8000 0000 0000 0000 0000 0000 0000

and
00000186 0000 0000 8000 0000 0000 0000 0000 0000

and even
00000186 0000 8000 8000 0000 0000 0000 0000 0000


AI said this

The Real Problem: Shared Logic Components

When multiple entirely separate blocks across two different boards fail on the exact same bit, it points directly to the logic gates handling that bit array line. You need to pull out the boards and inspect the Logic Multiplexers / Transceivers that drive Column 8.

Look at the logic chips at the bottom or sides of the memory board PCBs (typically 74-series logic). Specifically, look for:

1. 74LS244 or 74LS245 Octal Buffers/Transceivers: These handle the data bus lines coming off the RAM columns to send them back to the Lisa motherboard. A single failed gate inside a 74LS244 handling Data Line 15 will cause every single row block in Column 8 to fail simultaneously on that board.

2. 74LS153 or 74LS257 Multiplexers: These route the address strobe lines (RAS/CAS) across the row selections.

Not sure where 74LS244 is but I did examine and touch each chip RAM card still looks OK, and when I boot into Mac XL is shows 908K with a known good 512RAM card and my failing 512RAM.  But it doesn't load with just the 512RAM card (but it was in slot 2, with slot 1 empty).