The strange case of the Commodore 64 colour bands.

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stephen_usher
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Re: The strange case of the Commodore 64 colour bands.

Post by stephen_usher »

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.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
bigbloke
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Re: The strange case of the Commodore 64 colour bands.

Post by bigbloke »

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?
stephen_usher
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Re: The strange case of the Commodore 64 colour bands.

Post by stephen_usher »

This is the complete clock circuit:

251138-2of2-r.jpg
251138-2of2-r.jpg (315.05 KiB) Viewed 626 times

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
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
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rubber_jonnie
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Re: The strange case of the Commodore 64 colour bands.

Post by rubber_jonnie »

stephen_usher wrote: Tue May 10, 2022 5:50 pm 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?
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
bigbloke
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Re: The strange case of the Commodore 64 colour bands.

Post by bigbloke »

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!
stephen_usher
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Re: The strange case of the Commodore 64 colour bands.

Post by stephen_usher »

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.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
stephen_usher
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Location: Oxford, UK.
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Re: The strange case of the Commodore 64 colour bands.

Post by stephen_usher »

The chips and sockets have now arrived so I can see if they make any difference tonight.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
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rubber_jonnie
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Re: The strange case of the Commodore 64 colour bands.

Post by rubber_jonnie »

stephen_usher wrote: Thu May 12, 2022 1:57 pm The chips and sockets have now arrived so I can see if they make any difference tonight.
I'll be looking out for updates :)
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
BennehBoy
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Re: The strange case of the Commodore 64 colour bands.

Post by BennehBoy »

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...
stephen_usher
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Re: The strange case of the Commodore 64 colour bands.

Post by stephen_usher »

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.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
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