Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!asuvax!hrc!force!covertr
From: covertr@force.UUCP (Richard E. Covert)
Newsgroups: comp.sys.atari.st
Subject: Re: Mega 2 & TOS 1.4
Summary: yep
Message-ID: <4652906b.14a1f@force.UUCP>
Date: 19 Oct 89 15:36:05 GMT
References: <2706@hydra.Helsinki.FI>
Organization: gte
Lines: 26

In article <2706@hydra.Helsinki.FI>, viljanen@cs.Helsinki.FI (Lea Viljanen) writes:
> Is there a trick to installing TOS 1.4 into Mega 2's?
> I know a guy who has installed several ROM sets into all kinds of 
> ST's (520 ST - Mega 4). But only with Mega 2's he has problems;
> only 1 machine worked from the 6 he has done. Other types (even Mega
> 4's!) have worked OK.
> 
> So, who knows what's the crucial difference between Mega 2 and Mega 4
> so the same installing procedure doesn't work with Mega 2 but works
> with Mega 4?
> 
> Any help appreciated.
> Lea 'LadyBug' Viljanen           ____     University of Helsinki, Finland


Lea, there is a problem with replacing the 2 chip TOS 1.2 with a 6 chip
TOS 1.4. In some, not all but enough, Mega STs you need to replace the
74LS373 ics with 74 AS 373. repeat place the LS with AS. AS have a higher fan out
and can drive the additional load presented by the additional 4 EPROMS.

This is a kludge and is known by Atari, but it has to been done when you
install the new TOS if they fail. 

Good luck..

Richard (Thw Whiner (tm) ) Covert