Path: utzoo!attcan!uunet!lll-winken!lll-lcc!pyramid!cbmvax!hedley
From: hedley@cbmvax.UUCP (Hedley Davis)
Newsgroups: comp.sys.cbm
Subject: Re: 1764 expansion problems
Keywords: 1764, expansion, cbm
Message-ID: <3997@cbmvax.UUCP>
Date: 10 Jun 88 14:15:54 GMT
References: <1068@ihlts.ATT.COM>
Reply-To: hedley@cbmvax.UUCP (Hedley Davis)
Organization: Commodore Technology, West Chester, PA
Lines: 41

In article <1068@ihlts.ATT.COM> acthom@ihlts.ATT.COM (thomas) writes:
>
>The memory chips are good, they work in a 1750. Another 1764 controller
>chip does the same thing.
>
>
> (The current theory is that there are two versions of the controller
>  chip, and the ones that they put in the 1764 are the ones that
>  failed the 1750s, but could handle 256K.)
>
>Does anyone out there have any ideas?
>		Thanks, Al Thomas.

Sounds like something to do with your PCB. 

1)	Remove all ram from board, socket lower 256 K.
	Try old chips to verify you didn't bugger something in this
	step. Then once that works, try new chips in lower 256 K.
	If failure, then your rams are fubar.
	If good, then something is bogus about the second 256 K, and
	it probably has to do with the PCB patterns. You have an
	open or a short or a cold solder joint, or something silly
	like that.  
	Note that chip inside of the little square package, and the
	longer 64 pin package is actually the same, only the
	package has been changed.

	As for your comment that we are sorting controller chips,
	sorry bosco, but we don't. All chips shipped pass the same
	tests. One tester program.

One other comment, about that jumper.

	The jumper is misleadingly labeled. What it does is two things.
	#1)	cause a bit in the status register to read one or zero.
	#2)	Change the address multiplexing for the DRAMS for
		64Kx1 or 256Kx1 ram chips.
	The labeling is due to historical reasons regarding revised
	plans in the engineering & marketing issues surrounding the
	product line. ( Harumph ! :-) ).

Hedley