Re: option ROM into a 3032

From: Gerrit Heitsch <>
Date: Thu, 28 Sep 2017 11:15:44 +0200
Message-ID: <>
On 09/28/2017 10:26 AM, Francesco Messineo wrote:
> On Thu, Sep 28, 2017 at 12:17 AM, Ethan Dicks <> wrote:
>> On Wed, Sep 27, 2017 at 4:24 PM, Francesco Messineo
>> <> wrote:
>> If the inputs are good and there's no good output, this is a good
>> candidate.  It definitely has a lot to do with selecting the right
>> data at the right time.
> indeed UF6 was in a really bad shape. I've substituted with a good
> 74LS157 and now
> the video ram gets written correctly.
> The petester image shows a lot of bad DRAM and the video circuitry is
> still not working good:
> on every 8 columns, starting from the first, the character shape
> flickers. I have excluded the chargen ROM, but I need to go back to
> the schematic to understand what may be the problem here.

If the char ROM is good, take a closer look at the surrounding circuit. 
There should be a 74166 or 74165 shift register somewhere that 
serializes the output from the char ROM. If one of its inputs is bad, 
you'll get vertical bars or flickering every 8 pixels.

If you mean every 8 chars you have the whole char flickering, you should 
look at the address counter for the screen memory access.


       Message was sent through the cbm-hackers mailing list
Received on 2017-09-28 10:00:03

Archive generated by hypermail 2.2.0.