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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 »

Oh well, after warming up it went back to the original banding. Oh well.

Well, it can't be anything to do with the oscillator or the VIC-II. That leaves the 74LS629 or later in the circuit, in the modulator.

Well, when I replace the modulator with a by-pass board: https://videogameperfection.com/product ... eo-bypass/
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.
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Re: The strange case of the Commodore 64 colour bands.

Post by rubber_jonnie »

stephen_usher wrote: Tue May 03, 2022 9:17 pm Oh well, after warming up it went back to the original banding. Oh well.

Well, it can't be anything to do with the oscillator or the VIC-II. That leaves the 74LS629 or later in the circuit, in the modulator.

Well, when I replace the modulator with a by-pass board: https://videogameperfection.com/product ... eo-bypass/
Oh, that's rubbish :(

I know how you feel after my my 600XL shenanigans, getting ready to reassemble and finding out the problem can back after a while. It was my own fault though for not correctly disabling the original 3.5Mhz oscillator properly.

I guess it doesn't leave a lot to try any more.
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...
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Re: The strange case of the Commodore 64 colour bands.

Post by stephen_usher »

It looks like the modulator replacement board *may* arrive on Monday.
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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Re: The strange case of the Commodore 64 colour bands.

Post by rubber_jonnie »

stephen_usher wrote: Fri May 06, 2022 10:35 am It looks like the modulator replacement board *may* arrive on Monday.
Reminds me I need to fix my VIC-20 modulator. Just for kicks as the composite out is really quite nice.
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...
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Re: The strange case of the Commodore 64 colour bands.

Post by stephen_usher »

The C64 modulator replacement board has arrived, so all go for trying it 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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Re: The strange case of the Commodore 64 colour bands.

Post by mrbombermillzy »

For goodness sake. This MUST be the last thing left to try. Fingers crossed. :)
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Re: The strange case of the Commodore 64 colour bands.

Post by stephen_usher »

It is as far as I can see. There are merely a couple of ferrite bead links and ceramic caps (from what I remember) between the VIC-II and the modulator and that's it!
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: Mon May 09, 2022 1:39 pm The C64 modulator replacement board has arrived, so all go for trying it tonight.
Fingers all crossed for you!!
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...
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stephen_usher
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Re: The strange case of the Commodore 64 colour bands.

Post by stephen_usher »

Yeah, me too. Actually, other than the ferrite links there's nothing between the VIC-II and the modulator and nothing between the modulator and socket so if this doesn't fix things then nothing will.

I'm wondering if I could replace the UHF output using an Astec UM1286 modulator, tapping the composite and audio signals from the new board. That would give the best of both worlds.
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.
Top
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mrbombermillzy
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Re: The strange case of the Commodore 64 colour bands.

Post by mrbombermillzy »

If there's any more mucking about to be done after this, I would be tempted to do an RGB conversion of the signal (like the French/SECAM C64s had).

https://www-c64--wiki-de.translate.goog ... r_hl=en-GB

https://www-c64--wiki-de.translate.goog ... r_hl=en-GB
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