Re: mosaic screen on c64

From: Gerrit Heitsch <>
Date: Tue, 05 Aug 2014 18:53:30 +0200
Message-ID: <>
On 08/04/2014 11:08 PM, didier derny wrote:
> Thanks, a friend bought a c64
> For now I only have a small image around the 6569...
> According to this small image it's either

Ok, so it's a 250407 board.

The image of the screen tells us a few things... First, the CPU starts 
up and runs at least part of the ROM code, enough to program VIC so it 
attempts to display something. The mosaic looks like the color RAM 
doesn't get initialized (SRAMs like the 2114 start up with random 
contents) and since there are no visible characters at all, it looks 
like VIC doesn't see the char ROM.

So, my bet is the PLA or any MOS-TTLs. The latter were widely used on 
the 250407 and 250425 boards. If the board doesn't use 74LS257 but MOS 
7708, it's very likely that those are dead (They usually work for a 
short time after power up and then crap out). Replace with 74LS257.


       Message was sent through the cbm-hackers mailing list
Received on 2014-08-05 17:00:02

Archive generated by hypermail 2.2.0.