General Category > Lisa Troubleshooting and Repair
Lisa 2 Motherboards
anotherLISAguy:
You guys did such a great job in pointing out differences in the TwoPort card earlier, that I thought you could help with this curiosity.
Was reviewing some eBay images online and noticed two different types of Lisa 2 motherboards (not XL). While I understand different revisions may have different layouts and electronics, these have or don't have a series of resistors!
The first image is a Lisa 2 motherboard with resistors installed, the second image is an earlier revision motherboard without resistors installed!
This strikes me odd since the PCB clearly identifies locations for electronics where none exists in the second image.
It seems a bit more dramatic than the clipped R47 mod and I don't recall any 'that motherboard doesn't work with X' info.
Is there some functional difference between these motherboards?
TIA
sigma7:
Those are damping resistors on the parallel port to reduce the signals ringing, which affects the reliability of the ProFile.
The original Lisa 1 Motherboard design doesn't include those resistors; the holes used for the retrofit are vias and so not actually intended for installation of any parts; they were just the most convenient place to install the resistors.
The 2/10 Motherboard design includes the resistors, as does the Sapient version of the Lisa 1 Motherboard.
ried:
I have always wondered about this, and it's nice to finally know the answer. The left-most resistor has been added on one of my spare boards, too.
Photos for reference:
And one with no resistors at all:
anotherLISAguy:
--- Quote from: sigma7 on September 09, 2024, 04:29:35 pm ---Those are damping resistors on the parallel port to reduce the signals ringing, which affects the reliability of the ProFile.
The original Lisa 1 Motherboard design doesn't include those resistors; the holes used for the retrofit are vias and so not actually intended for installation of any parts; they were just the most convenient place to install the resistors.
The 2/10 Motherboard design includes the resistors, as does the Sapient version of the Lisa 1 Motherboard.
--- End quote ---
AH - so the initial L1 design had hole placement in place as a potential modification (for dampening), and later L2 builds (not L2/10/XL) added them to ensure dampening - or do I have that backward - either way, both motherboards are functionally equivalent except for the latter having dampening added to that port
Thanks for explaining that curiosity! :)
stepleton:
--- Quote from: anotherLISAguy on September 10, 2024, 09:03:02 am ---AH - so the initial L1 design had hole placement in place as a potential modification (for dampening)
--- End quote ---
Not exactly... Apple got lucky. The holes were already there, but they weren't for components: they were vias, ways of connecting a circuit trace on one side of the board to a trace on the other side. But a component leg fit inside these vias, and they happened to be in just the right places, so they could stick in resistors without having to come up with a new board design. This kind of low-price modification is sometimes called a "bodge".
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