Amiga A500 Rev 6, Black and white only

[Swivel]

Hello all, Driving me nuts.

So.

Amiga A500 rev 5, a520 TV, All good color etc.

Amiga A500 rev 6a, a520 tv, no color.

So TV and A520 ok.

Note this A500 rev 6a had a had a changer unit that had a 1.3 and 2.0 roms.
2 cables out of it. , 1 to the odd cia (pin8), and one to the gary chip )pin 5).

Thought it was that, But removed and just 1 of the roms, still no color.

Any Ideas as I would rather use the rev 6a system,

Tomo

[lesta_smsc]

Just making sure they are both PAL/NTSC? Something as simple as clock frequency on the wrong TV could also cause this.

Easiest way to overcome this is to use RGB out. This will also tell you if the colour circuitry is intact.

[derSammler]

PAL/NTSC does not matter for color when using the A520 TV modulator, as that is fed with RGB. Actually, it does not matter for the A500 at all, as the A500 does not have any color encoding circuitry for PAL or NTSC. That's why composite output is always b/w.

I would blame the A520, even if it works with the other A500. Best way to test would be to connect RGB directly to the TV. But I assume the TV does not have SCART, right?

[LIV2]

The A520 derives it's colour clock from the systems CCK - so matters not only whether the machine is PAL/NTSC but also that the Modulator matches whichever standard is being used.

If both Amigas are the same region then check connectivity of CCK on Pin 15 of the video connector through E402 and back to U41

[alenppc]

I am assuming your A520 is a PAL variant, in which case you need to have an A500 with a 28.375 MHz oscillator. If your A500 has a 28.6363 MHz oscillator (ntsc model), you will get a B/W output out of a PAL A520.

[Swivel]

Originally Posted by derSammler

PAL/NTSC does not matter for color when using the A520 TV modulator, as that is fed with RGB. Actually, it does not matter for the A500 at all, as the A500 does not have any color encoding circuitry for PAL or NTSC. That's why composite output is always b/w.

I would blame the A520, even if it works with the other A500. Best way to test would be to connect RGB directly to the TV. But I assume the TV does not have SCART, right?

Hello,No Scart, But I dont think it is the A520, as I have 2 of them with the same result.
I feel it is something to do with the A500 rev 6a itself

[Swivel]

Originally Posted by alenppc

I am assuming your A520 is a PAL variant, in which case you need to have an A500 with a 28.375 MHz oscillator. If your A500 has a 28.6363 MHz oscillator (ntsc model), you will get a B/W output out of a PAL A520.

How would you check ??

[Swivel]

Originally Posted by LIV2

The A520 derives it's colour clock from the systems CCK - so matters not only whether the machine is PAL/NTSC but also that the Modulator matches whichever standard is being used.

If both Amigas are the same region then check connectivity of CCK on Pin 15 of the video connector through E402 and back to U41

I will tonight. Thanks.

[alenppc]

Originally Posted by Swivel

How would you check ??

Check what's printed on the oscillator can on the motherboard. I also wonder if the oscillator frequency might have drifted too much to get the colourburst at the correct frequency.

[Swivel]

Originally Posted by alenppc

Check what's printed on the oscillator can on the motherboard. I also wonder if the oscillator frequency might have drifted too much to get the colourburst at the correct frequency.

28.37516 MHz

[alenppc]

Originally Posted by Swivel

28.37516 MHz

Ok, so you have a PAL Amiga and presumably a PAL A520, so the problem lies somewhere else. It could be that the crystal is no longer providing the correct frequency due to aging or there could be another fault.

[Jope]

I've revived some black and white A520s by swapping the crystal inside the A520, but who knows.

[Swivel]

Originally Posted by alenppc

Ok, so you have a PAL Amiga and presumably a PAL A520, so the problem lies somewhere else. It could be that the crystal is no longer providing the correct frequency due to aging or there could be another fault.

Bummer, As would rather use the rev 6a than the rev 5, LOL