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mpfjr

Macintosh Plus memory upgrade help please.

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Howdy there folks!

 

Running into a bit of a problem that I can't work out myself and was hoping you could help.

 

I had a bad Plus motherboard so I bought another one on ebay.  It came missing both resistors R8 and R9.

 

But since I wanted to install 4MB that was fine!

 

Well it will not boot up with any of the 1MB sims I have installed.  I bought some on ebay that work fine in my SE but those same modules do not work in the plus.  I have 4x 1MB 80ns and 4x 1MB 70ns modules.

 

So I took the 256K modules from my old one, put them into the new one (talking about motherboards here) and it boots to happy face icon but no further.  Insert a disk, it reads the disk but the desktop and "welcome to macintosh" do not come up.

 

So I removed the R8 aka 256K resistor from the old one, soldered it onto the new one, and it boots up just fine with 1MB total memory.

 

All I can think of is that there is something weird going on where the 1MB memory just won't be recognized by the Plus motherboard.    Capacitors on the motherboard looks fine, analog boards (I have two) I re-capped recently and they both work fine too.    The only weird thing is that snipping the resistor and plugging in any combination that includes 1MB sims it will not boot up.  What do you suggest I try?

 

Thank you.

Edited by mpfjr

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3 hours ago, mpfjr said:

Howdy there folks!

 

Running into a bit of a problem that I can't work out myself and was hoping you could help.

 

I had a bad Plus motherboard so I bought another one on ebay.  It came missing both resistors R8 and R9.

 

But since I wanted to install 4MB that was fine!

 

Well it will not boot up with any of the 1MB sims I have installed.  I bought some on ebay that work fine in my SE but those same modules do not work in the plus.  I have 4x 1MB 80ns and 4x 1MB 70ns modules.

 

So I took the 256K modules from my old one, put them into the new one (talking about motherboards here) and it boots to happy face icon but no further.  Insert a disk, it reads the disk but the desktop and "welcome to macintosh" do not come up.

 

So I removed the R8 aka 256K resistor from the old one, soldered it onto the new one, and it boots up just fine with 1MB total memory.

 

All I can think of is that there is something weird going on where the 1MB memory just won't be recognized by the Plus motherboard.    Capacitors on the motherboard looks fine, analog boards (I have two) I re-capped recently and they both work fine too.    The only weird thing is that snipping the resistor and plugging in any combination that includes 1MB sims it will not boot up.  What do you suggest I try?

 

Thank you.

 

 

As it turns out the Plus, as I suspected, does not like fast memory.  I found 4x 100ns 1MB modules in my OTHER SE and swapped them.  Both computers now report 4MB of memory.  The Plus with 100ns and the SE with 70ns.

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