The strange case of the Commodore 64 colour bands.

[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/

[rubber_jonnie]

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.

[stephen_usher]

It looks like the modulator replacement board *may* arrive on Monday.

[rubber_jonnie]

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.

[stephen_usher]

The C64 modulator replacement board has arrived, so all go for trying it tonight.

[mrbombermillzy]

For goodness sake. This MUST be the last thing left to try. Fingers crossed. :)

[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!

[rubber_jonnie]

The C64 modulator replacement board has arrived, so all go for trying it tonight.

Fingers all crossed for you!!

[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.

[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