Reconstructing an auctioned Lisa

[sigma7]

I'm not having much success.

In IMG_4248.jpeg, it looks like the orange wire on the bottom is connecting pin 7 and pin 11... which would be incorrect.

If jumpers on the bottom aren't working on the top, check that the chip is making good contact in the socket. In particular, a leg may be folded under the chip instead of going into the socket.

Beware that a trace that looks intact may be disconnected from the other side because the plating inside a hole was damaged during desoldering.

[berskyboy]

not getting checkers anymore, but it booted briefly and gave

00000186  0000 0000 FF00 FF00 0000 0000 0000 0000

and then put the good known RAM in slot 1, back RAM slot 2 is goes back to checkers.

YouTube:

https://www.youtube.com/shorts/2qkkvo3cwkU

[sigma7]

In your video, you check continuity for pins 1-8 to the chip on that side (column 7), and for pins 9-16 to the chip on the other side (column 9).

There could be a broken trace still, separating column 9 from column 7. So check there is the same continuity between those chips, or check each pin of the replacement to the chips on both sides (not just the closer side).

Similarly, the traces that go to the chip "below" (pins 2 & 14), may not continue to the chip above, so check these pins connect to both the chip below and the chip above.

[berskyboy]

Hi

In your video, you check continuity for pins 1-8 to the chip on that side (column 7), and for pins 9-16 to the chip on the other side (column 9).

There could be a broken trace still, separating column 9 from column 7. So check there is the same continuity between those chips, or check each pin of the replacement to the chips on both sides (not just the closer side).

Similarly, the traces that go to the chip "below" (pins 2 & 14), may not continue to the chip above, so check these pins connect to both the chip below and the chip above.

Hi, thanks for your help on this.  I thinking after tinkering with the RAM and looking at the diagrams I can see the following

the new chip should have connectivity on the following pins

LEFT CHIP                                  REPLACEMENT      RIGHT CHIP

9  (connected should be beep)     9            8      8 (connected should be beep for continuity)
10 (connected should be beep)    10          7      7 (connected should be beep for continuity)
11 (connected should be beep)    11          6      6 (connected should be beep for continuity)
12 (connected should be beep)    12          5      5 (connected should be beep for continuity)
13 (connected should be beep)    13          4      4 (connected should be beep for continuity)
14 (connected to TOP/BOTTOM)  14         3      3 (connected should be beep for continuity)
15 (connected should be beep)    15          2      2 (is connected to TOP and BOTTOM chip)
16 (connected should be beep)    16          1      1 (not connected, no beep for continuity)

here's the video
https://www.youtube.com/shorts/VKErDlzzJ_Q

[sigma7]

In your video, you check continuity for pins 1-8 to the chip on that side (column 7), and for pins 9-16 to the chip on the other side (column 9).

There could be a broken trace still, separating column 9 from column 7. So check there is the same continuity between those chips, or check each pin of the replacement to the chips on both sides (not just the closer side).

here's the video

You've got the right idea, so maybe you've already checked this (but it isn't included in the video):

In the video, you checked that pins 3-8 are connected through all 3 chips (the replaced one and the ones on each side), but you didn't show that you checked that pins 9-13, and 15 are connected to the chips on both sides (the video shows checking only the column 9 chip to the column 8 replacement).

So check pins 9-13 & 15 connect from column 7 to column (8 or 9).

If still no success, please do the self-test again and report the breadcrumb codes in memory as they are now.

[berskyboy]

In the video, you checked that pins 3-8 are connected through all 3 chips (the replaced one and the ones on each side), but you didn't show that you checked that pins 9-13, and 15 are connected to the chips on both sides (the video shows checking only the column 9 chip to the column 8 replacement).

So check pins 9-13 & 15 connect from column 7 to column (8 or 9).

If still no success, please do the self-test again and report the breadcrumb codes in memory as they are now.

Correct I did just that, all 16 pins pass on the left and right chips (except pins 2 and 14 they pass on the top and bottom chips)

Here's the code I get

https://www.dropbox.com/scl/fi/wjbvmz2neplmauowlf9ih/IMG_4266.jpeg?rlkey=2xg9lyexwrqzo7eo4bk0kydv8&st=3wt5yc53&dl=0

[sigma7]

The breadcrumbs you've reported are

Code Select Expand

00000186  0000 0000 ff00 ff00 0000 0000 0000 0000
00000196  0000 0000 0000 0000 0000 0000 0000 0000
The ff00 codes indicate that bits 15-8 are failing, ie. the entire high byte. The chip replacement was in column 8 on the board, which is the high byte side.

The ff00 codes appear in the third and fourth positions, which (for an Apple 512K memory board) would be either rows D & E or rows B & C, depending on the slot the board is in.

From message #15 of this thread, it looks like you are/were getting these codes when the bad board is in slot "MEM 1" (closer to the CPU board), with "MEM 2" empty. That suggests rows D & E, which seems most plausible since the chip replacement was in row D.

The RAM array has signals that daisy chain through the columns of chips, as well as through the rows, similar to a hatch pattern.

You've checked the most straightforward signals that go across the columns and signals that go up and down the rows, but there are also connections that join the cross-wise row signals to the rows of chips above and below.

Some of those horizontal - vertical intersections occur at the replaced chip, and breaking one (or more) of those could affect rows D&E.

Check that the following pins connect the replaced chip (U8D) with the one 'above' it in Row E (U8E) , and also with the one 'below' in Row C (U8C):
('Above' and 'below' in the sense that berskyboy is taking pictures and videos with the card edge connector away from the camera, the opposite of how it is installed in the Lisa)

Pins 5, 6, 9, 10 - These are cross-point connections where traces connect horizontally AND vertically at U8D.

Also check pin 11, as this is also a cross-point connection, but at a via under the chip rather than one of the legs, so unlikely to be the problem.

If still no success, check for short-circuits between adjacent pins.