Pardon me for asking...

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clh333
Retro freak
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Pardon me for asking...

Postby clh333 » Sat Sep 30, 2017 11:51 am

I'm noob and have only recently posted here but have three Ataris - two ST520s and one ST Mega 2 that I just acquired. I also have two SM and one SC monitors. The SC has a problem (overheating) but that's not the reason for this post.

I read all the posts in the sub-forum and found a great deal of useful information there, but not the information I was looking for. So pardon me for asking a basic question: How do I split the case?

I want to see what condition the Mega's board is in, whether there are any caps that look bad or damage to the traces. I removed the case screws from the bottom and can lift the top half of the case at the back but it seems to be fastened in front. Or perhaps it is meant to be pushed forward, free of the FD, but this one is not moving easily and I don't want to break the case by forcing it.

Any suggestions would be greatly appreciated. Thanks.

-CH-

Atarieterno
Captain Atari
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Location: Spain

Re: Pardon me for asking...

Postby Atarieterno » Sat Sep 30, 2017 12:13 pm

Also remove the screws that holding the floppy drive.
ST/fm/e, STacy, Mega ST/e, TT, Falcon, C-Lab MKX... and more music tools.

guus.assmann
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Location: Ede Netherlands

Re: Pardon me for asking...

Postby guus.assmann » Sat Sep 30, 2017 7:11 pm

Hello clh333,

Normally, removing all the screws that are in a "square hole" will enable you to take an Atari computer apart.
For the Mega ST, lift the back as far as you can and try to slide the plastic to the front.
This will enable you to move it past the front of the floppy drive.
It helps to insert a disk in most cases.
There may be one screw behind a waranty seal.

BR/
Guus Assmann
Guus Assmann

clh333
Retro freak
Retro freak
Posts: 11
Joined: Sat Oct 03, 2015 11:47 am

Re: Pardon me for asking...

Postby clh333 » Thu Oct 05, 2017 2:41 pm

Thank you both for your replies. I succeeded in opening the case and exposing the motherboard (pictures attached). Overall looks good: traces clean, no evidence of leaking caps or overheating. It's clear that repairs were made at some point in the past, however.

I don't have a reference that shows me the board layout. Can anyone recommend one?
But I can recognize some components; ROM, RAM, CPU, FDC, etc.

A few questions:
-ROM C101629/30 is TOS 1.2.1, apparently. Is this the best option or would a later version be recommended? Can the ROMs be burned to an EPROM and substituted? I have a burner; which EPROM and which image?
-The power supply looks pretty small. What is the output? Is this a common point of failure? Is there a replacement or upgrade?
-RAM (M 411024; 16 pcs 1Mx1) is not socketed but soldered to the board. Is there a RAM expansion short of re-soldering?
-Empty headers at J15, J17 and J18: What are they for?

Sorry to be so clueless but greatly appreciate any advice given.

Thanks again,

-CH-

STM2_2.jpg
STM2_1.jpg
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