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Apple iie Platinum Garbled Screen

M

masterpigeon

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Oct 7, 2016
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I finally powered on the apple iie Platinum i bought a couple months ago but of course it didn't work. The first time i powered it on it beeped and displayed the normal "Apple //e" at the top of the screen but with no cursor. After rebooting it all it would display was random characters. I pulled all the socketed chips and reseated them, the tops of the pins where they enter the ic were all slightly corroded. I mucked around with the thing for about 20 minutes pulling
chips and flipping the little switch under the front of the case with varied results. On one of the reboots it displayed a blank screen with "MMU" in the centre.
Another time it displayed "SYSTEM OK" surrounded by "H". Not really sure what it means.

IMG_20180101_100109.jpgIMG_20180101_100208.jpgIMG_20180101_100245.jpgIMG_20180101_100523.jpgIMG_20180101_102145.jpgIMG_20180101_102401.jpgIMG_20180101_102608.jpgIMG_20180101_102932.jpgIMG_20180101_103035.jpgIMG_20180101_103346.jpg
 
Looks like it might be a bad RAM chip

If you are able to program a 2764, this diagnostic ROM I wrote might help you narrow it down
https://drive.google.com/open?id=0B8aVm3oIO3icS3lBNWp3QTFDSTg

It replaces the F0 ROM on your board and does some basic RAM tests and displays the results on the screen as well as beeping the speaker to indicate which test failed (sometimes faulty RAM prevents a readable display).
 
unfortunately i can not program a 2764, so i guess I'll just replace the ram on the board and see if it does anything.
 
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RAM in the 2e isn't socketed and in a lot of production runs they bent over the IC legs before soldering which makes them a pain in the ass to remove without damaging the pcb.
I use a desoldering station and avoid removing chips when I can. On the plus side the platinum uses only 2 RAM chips not 8
 
Could I piggy back the new chips onto the old chips the test them before I bother desoldering them?
 
In photo #6 of 10 you can see the code RAM 1 0 1 0 0 0 1 1 so I agree with David that it's a ram problem. Photo #9 has a bunch of "0" which is $B0 when it should be spaces $A0 which is a stuck bit 4 of ram.
MMU is the Memory Management Unit chip which interfaces with the ram. I suppose bad ram could cause a false MMU failure code. There have been more failure reports of ram than MMU chips.
I think the Platinum has two 64K by 4 bit ram chips. If you can figure out which chip has bit 4 that would be the one to change first.

Larry G
 
No, I haven't. I should probably do that. The power supply does make a squeaky sound when turned off.
 
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