30 replies to this topic

[NeilTheDruid]

mamejay, on Tue May 17, 2011 7:04 PM, said:

As for the points on the TIA and Maria you just need continuity direct to the TIA and Maria.


BTW have you tried on any other TV to see if you get a better picture?

Unfortunately, I don't have another TV to try.

I'm pretty sure that every point on my 7800 is correct except the sync. When the picture does stop rolling and distorting the brightness and colour is just where you'd want it. I am just really struggling to find a point where I can permanently stop the rolling. Finding a point with little or no resistance in between the sync pins of the maria and tia seems impossible.

[NeilTheDruid]

Hmmm, looks like my suspicions are correct. I got bored of messing around so I soldered the sync wire directly to the TIA. I know it's not really "standard practice" but I get exactly the picture I want - out of the 2600 games at least. Pulling the same trick on the MARIA doesn't seem to work though. So it seems the problem is almost definitely with the sync line, If anyone has any suggestions as to where else I could put it, that would be great.

[mamejay]

There should only be one sync line for both 2600 and 7800.
i would start looking at the 7800 Chroma point and confirm that it is fine.

Also what are you getting when running 7800 games? Is the screen still scrolling and B/W?

[NeilTheDruid]

At the moment I'm getting a viewable picture from the maria, but there are rolling diagonal white lines, so it's not perfect. I might take a picture for you guys to show you how annoyingly close I am to getting it right.

[NeilTheDruid]

Alright chaps, this is what I've got so far. To achieve this I had to adjust from the ops' plans slightly. I had to move the 2600 chroma as mamejay suggested. I moved the Luma0 connection over one point to the left as there was no continuity to the Luma0 pin on the TIA. I am currently getting sync from pins 9 and 10 of the LS32 above the MARIA. I'm pretty pleased with 2600 games (excuse my crap camera - it does look good in person). 7800 games still have diagonal white lines and flickering, I'm not quite sure how to fix this yet as I already have direct continuity with the sync pin on the MARIA. Any suggestions on how to fix this would be massively appreciated.

Nearly there!

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[NeilTheDruid]

Ok guys. I finally figured out a fix for my issue, I thought I'd share so anyone possibly having the same problem could try it.

I basically swapped the 750ohm resistor next to the diode on the OPs circuit for a 10k trim pot, like in saundbys mod. Using this allows you to adjust the sync in until the flickering mess disappears.