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A Macintosh Plus with RAM problem symptoms (but it's not that)


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I have two Macintosh Plus, one fully functional, the other not (I will call the working Macintosh Plus 'good', while the non-working one I will call 'bad').
I state that the RAM banks of 'bad' have been tested on the logic board of 'good' and work.
The operations that have been done on 'bad' are:
Change capacitors C1 and c2 in the analog board, plus the replacement of the two RIFA (which generally have exploded). I went over all the critical pins (connectors etc.) related to the solderings of the analog board, including the soldering of the sockets that allow the insertion of the ram into the logic board.
Tests done:
1) I put the analog board of 'good' with the logic board of 'bad'. Result? When turned on it makes a noise from the speaker, like a gigolio, black screen.
2) I put the analog board of 'bad' with the logic board of 'good'. Result? - With RAM it displays vertical lines (photo 1) - No RAM displays garbled screen (photo 2)
3) I put the analog board of 'bad' with the logic board of 'bad' Result? - With the first two rows of RAM banks, a short sound is heard and written 02FFFF (photo 3) (this I deduced is normal because the rest of the RAM is missing) - If I put the other two banks, no sound is heard and the screen has very thin horizontal lines (photo 4)

foto1.jpg

foto2.jpg

foto3.jpg

foto4.jpg

Edited by Roberto
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Somehow the situation has changed. From my Macintosh Plus (the 'bad' one so to speak) I see alternate screens, similar as in the attachment, with some noise coming from the speaker. And here I stopped. Have any of you had a Plus with these symptoms?

e4aefa17-be24-4b6d-abd3-1fa4c4bb483f.jpg

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Fault code is related to a Ram issue, but this kind of behavior can also be related to bad Rom, as the Rom is socketed, i will swap Rom in the Good Plus to see if Rom is ok or not

Edited by bibilit
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Ok, but have you the exact same issue when swapping Roms around ??

 

What happens when the "Bad" Roms are fitted to the "Good" board ?? (will not hurt the board)

 

If not, the only issue i can see is that one of the logic chips handling the ram memory is bad, hence throwing fault codes related to bad ram when ram is ok and displaying weird display patterns ramdomly

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I should change the title of this post to ... A Macintosh Plus with RAM problem symptoms (but it's not that and neither does the ROM). I tried to put both the ROMs of the good in the bad and vice versa and the screen of the bad macintosh has vertical lines (the good macintosh works well with the bad's roms).

I think it's like you said bibility ...

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A last question, what kind of memory is present in the "Bad" unit ? 

 

The default type is 4 sticks of 256 k each, so giving the 1 Mb standard setup.

 

On the upper left side of the Logic board, a modification is supplied to go other this figure. can be an issue here as you have not each time the same screen.

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