Re: option ROM into a 3032

From: Francesco Messineo <>
Date: Thu, 28 Sep 2017 12:48:03 +0200
Message-ID: <>
On Thu, Sep 28, 2017 at 11:15 AM, Gerrit Heitsch
<> wrote:
> 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.

it's every 8 chars. Now I first have to replace the UD9 socket (I
hope). After swapping the EPROMs a few times, the PET no longer
execute anything, so I guess it's that crappy socket.
I'll have a look at that counter after I fix the ROM problem (unless
something else died).
>  Gerrit
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Received on 2017-09-28 11:00:03

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