exxos's Atari, Amiga & retro forum

The 74LS74 now socketed. I now need some more 14 pin sockets. I've ordered a new chip from Retroleum so it may arrive by the end of the week.

I also reflowed all the capacitor and resistor legs.

I haven't read the whole thread (TL;DR :) ) and I know next to naff all about C64s, but that last picture of the VIC chip, there is a resistor jammed into the left side of C86, that doesn't have any silk screen reference I can see. Just wondering if that's been ruled out as a cause?

This is the complete clock circuit:


The resistor in question is R101, which for the Rev 1 VIC-II is 22 Kohm. It's just a pull-up resistor. For the rev 3 VIC-II it's removed.

I've replaced the crystal Y1, C70 and U31

stephen_usher wrote: 10 May 2022 17:50 Well I've installed the new chip and...

There

Are...

No changes. It's just the same.

I'm leaning towards the conclusion that it's a "feature" of this particular motherboard revision.

Damn, that's frustrating. Maybe time to go for the 193 as well?

Thanks for the circuit and explanation of R101. Looking back at that picture from page 11, pin 1 of the MC4044 looks extremely janky, and that is a critical element of the feedback loop to the LS629. Might be worth looking at DOT-CLOCK and seeing how stable it actually is? Otherwise I got nothing. PLLs and stuff is a black art I am not fully versed in!

It's OK, it's just slightly under soldered.

Anyway, I've ordered this morning a 74LS193 and a whole load of 14 pin sockets as I've run out. I think I'll desolder and socket the rest of the chips in the can. Once the 74LS74 and 74LS193 have been replaced the only chip left will be the MC4044P.

The chips and sockets have now arrived so I can see if they make any difference tonight.

stephen_usher wrote: 12 May 2022 13:57 The chips and sockets have now arrived so I can see if they make any difference tonight.

I'll be looking out for updates :)

I seem to recall Bill Herd stating that the C64 used 'Commodore Chroma', and that the 1701 monitor 'corrected' that so that colour looked good - on anything else it would look bad... could this just be that issue? Ie design...

Not really, as what would be described there would be a constant change for the whole screen, not bands where the chroma signal is varying frequency across the image. It's also on the RF.