30 Jan
2012
30 Jan
'12
9:44 a.m.
I have a malfunctioning C64 that I would like to repair that is exhibiting the most odd of
behaviors.
The system operates fine, except displayed fonts cycle through the color palette. If you
remember the old atari 2600 game "Adventure" its behaves like the chalice does,
every second or so changing colors.
I haven't started probing the system at all, and although I can use a soldering iron,
my troubleshooting skills are pretty rusty. I was considering this a good project for a
refresher.
Sound doable, or is it likely I'll be looking to replace lots of components on the
board?
Kevin
30 Jan
30 Jan
10:59 a.m.
I know following up your own request is kinda taboo, but I should have shared more
information...
I am guessing that the problem is with the Color RAM (SRAM) in slot U6. This model of C64
has socketed components, but I am not sure U6 is one of these. The other possible issue
is PLA U17.
As the problem never goes away, perhaps it is more than this.
Is there a good vendor to get replacements this late in the game?
Kevin
From: tpresence at hotmail.com
To: cctech at classiccmp.org
Subject: Commordore 64 character color cycling
Date: Mon, 30 Jan 2012 10:44:53 -0700
I have a malfunctioning C64 that I would like to repair that is exhibiting the most odd of
behaviors.
The system operates fine, except displayed fonts cycle through the color palette. If you
remember the old atari 2600 game "Adventure" its behaves like the chalice does,
every second or so changing colors.
I haven't started probing the system at all, and although I can use a soldering iron,
my troubleshooting skills are pretty rusty. I was considering this a good project for a
refresher.
Sound doable, or is it likely I'll be looking to replace lots of components on the
board?
Kevin
31 Jan
31 Jan
9:06 a.m.
On Mon, Jan 30, 2012 at 1:59 PM, Kevin Reynolds <tpresence at hotmail.com> wrote:
I know following up your own request is kinda taboo, but I should have shared more
information...
I am guessing that the problem is with the Color RAM (SRAM) in slot U6. ?This model of
C64 has socketed components, but I am not sure U6 is one of these. ?The other possible
issue is PLA U17.
As the problem never goes away, perhaps it is more than this.
The Color SRAM is a 2114. Very ordinary and, in my experience, prone
to failure.
If you have another C-64, you could try swapping the PLA. You will
need an 18-pin socket for the SRAM. The chips are available from a
number of surplus places like Unicorn Electronics, BG Micro, and more.
Speed ranges for the 2114 are, IIRC, 250ms-450ms. I don't remember
what speed the C-64 requires, but you can typically sub a faster chip
than the circuit requires.
-ethan
9:23 a.m.
On Jan 31, 2012, at 12:06 PM, Ethan Dicks wrote:
The Color SRAM is a 2114. Very ordinary and, in my
experience, prone
to failure.
If you have another C-64, you could try swapping the PLA. You will
need an 18-pin socket for the SRAM. The chips are available from a
number of surplus places like Unicorn Electronics, BG Micro, and more.
Speed ranges for the 2114 are, IIRC, 250ms-450ms. I don't remember
what speed the C-64 requires, but you can typically sub a faster chip
than the circuit requires.
Jameco has 200ns ones for $2.49 each:
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_38973_-1
I'm not familiar with BG Micro (yet), but I know Unicorn has a hefty minimum, which
Jameco does not (while you're there, though, you might as well pick up the socket as
well and maybe some spare parts (like more 6502s).
- Dave
9:39 a.m.
I'm not familiar with BG Micro (yet), but I know
Unicorn has a hefty
minimum, which Jameco does not (while you're there, though, you might as
well pick up the socket as well and maybe some spare parts (like more
6502s).
Not long ago, Jameco had commodore PLAs for a song (something like a
dollar or less). I know a brazilian that bought 50 :o)
But remembering - You can put a 27C512 EPROM with a special bin in place
of a PLA! Google is your (best) friend! :D
11:58 a.m.
I know following up your own request is kinda taboo=2C but I should have sh=
ared more information...
I am guessing that the problem is with the Color RAM (SRAM) in slot U6. Th=
is model of C64 has socketed components=2C but I am not sure U6 is one of t=
hese. The other possible issue is PLA U17.
As the problem never goes away=2C perhaps it is more than this.
Is there a good vendor to get replacements this late in the game?
IIRC some (all?) C64s use a 2114-type RAM for the colour information. If
that''s the case, change it. I've had more problem with that sort of chip
than any other component ;-). I've lost count of thew number of things
I've had to fix by replacign one or more 2114s.
If it's not socketed, don't worry. If your desodlering skills are not up
to much, then cut the pins off the old IC close to the package, remvoe
the packagem, and remove each pin separately. Grab the pin on the top
side of the board with a pair of fine pliers, melt the solder on the
other side and pull the pin out. Then clear out the holes using a solder
sucker from the top side while heatign the solde on the bottom side.
I'd ft ta socket. A turned pin (machined pin I think you call them)
socket. While a socket is less reliable than a soldered-in chip, I've
never hadn a problem from a turned pin socket (that is not true of
cheaper formed-pin sockets!), so I think it's sensible to fit one unless
there are good electrical reasons (such as stray capacitance) not to.
That doesnt' apply here.
-tony
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