Path: utzoo!attcan!uunet!cbmvax!ditto
From: ditto@cbmvax.UUCP (Michael "Ford" Ditto)
Newsgroups: comp.sys.tandy
Subject: Re: Major illness in Mod 4
Summary: Can't execute boot code.
Keywords: Mod4
Message-ID: <4519@cbmvax.UUCP>
Date: 19 Aug 88 03:15:20 GMT
References: <2722@hubcap.UUCP>
Reply-To: ditto@cbmvax.UUCP (Michael "Ford" Ditto)
Distribution: na
Organization: Commodore Technology, West Chester, PA
Lines: 35

In article <2722@hubcap.UUCP> oolidjr@hubcap.UUCP (Joe Moll) writes:
>From: jnp@calmasd.GE.COM (John Pantone)
>>
>>Symptoms:  Put boot disk in drive - Power up - Drive light comes on,
>>drive spins - garbage on screen and no boot.  Cannot boot in Mod I
>>mode (reset switch while pressing break key) either.

>First of all, you prob. don't have any ROM problems. The ROMs used in
>the old Mod 3's and Mod 4's are tanks.  You prob. have a dead disk
>controller chip.  I had the same trouble with my old Mod 3 and the new
>chip did the job.  

I am assuming that the "garbage on screen" is normal alpha&graphic
characters in 16x64 or 24x80 format, rather than static or a rolling
picture or something like that.

I seriously doubt the disk controller diagnosis...  Based on my
experience hacking ModI/III/4 hardware, garbage on the screen and drives
spinning mean that the CPU can't run the boot code.  Unfortunately,
this could be caused by almost anything, like bad RAM, bad ROM, or a bad
CPU.  About the only things you don't have to suspect are disk, video,
and power supply.  Likely and/or easy things to suspect/replace would
be RAM, CPU, and anything that is socketed.  CPU's don't flake out very
often, so I'd suspect RAM first, then anything that might have been
replaced recently.  If you have 128K, try swapping chips from the first
bank to the second.

Sorry I can't give an easy solution.
-- 
					-=] Ford [=-

	.		.		(In Real Life: Mike Ditto)
.	    :	       ,		ford@kenobi.cts.com
This space under construction,		...!ucsd!elgar!ford
pardon our dust.			ditto@cbmvax.commodore.com