On 09/28/2017 10:26 AM, Francesco Messineo wrote: > On Thu, Sep 28, 2017 at 12:17 AM, Ethan Dicks <ethan.dicks@gmail.com> wrote: >> On Wed, Sep 27, 2017 at 4:24 PM, Francesco Messineo >> <francesco.messineo@gmail.com> 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. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2017-09-28 10:00:03
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