15 Dec
2009
15 Dec
'09
8:03 a.m.
The entire screen is having the trouble.
(it is odd that when it asks me to mount the disk, the !'s are
inverse...as soon as I put the disk in, they become normal-video !'s.
Also, the oddly swapped around characters...
How easy is it to pull those chips and swap them around?
Looking at the web page, do I need just plain 2114's? (I see several
variations of them including different speeds and low-power etc)?
(I've never swapped chips before..hence the questions).
Thanks.
-Bob
-----Original Message-----
From: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] On Behalf Of Mr Ian Primus
Sent: Tuesday, December 15, 2009 9:55 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: trs-80 model II trouble
--- On Tue, 12/15/09, Alexandre Souza - Listas <pu1bzz.listas at gmail.com>
wrote:
Use the force :)
You know that a byte has 8 bit.
You know that a space (chr 32) is
00100000 in binary
You know that a exclamation point (chr
33) is 00100001 in binary
You know that in the place of a space,
there is a ! on the screen
So, you know that the least significant
bit, or D0 line, is stuck in "1"
Get the schematic and see which 2114 is
connected to the A0 line. Change it, and you're set :o)
Don't you mean, D0 line? <grin>
According to the schematics, both U21 and U22 are on the D0 line.
One thing I just thought of - is the ENTIRE screen affected, or just
half of it? If one chip had a stuck line, it should only mess up half
the screen.
In any event, the chips should be socketed, so doing a couple quick
swaps should narrow it down quickly.
-Ian