Amiga 1000 color strangeness

This shows the behavior that my Amiga 1000 is currently exhibiting. Green and Blue seem like they've dropped a bit of color depth. when the slider is above 50%, it's bright, when it's below it's dark. And when you're sliding in the bright or dark regions, instead of increasing with each step, it's alternating between slightly darker and slightly lighter.

Meaning, instead of steps like "1 2 3 4 5 6 7 8" it's instead "1 2 1 2 7 8 7 8" and such.

I think it might be the 74HC244 chips in the video circuitry, but I'm not sure. I've already swapped the Denise with another one, and it didn't change anything.

If anyone has any ideas, I'm all ears.

Category:

Howto & Style

Tags:

• amiga
• 1000
• repair

[yorgle]

Hi! The Ami has been on a shelf, since I moved and didn't have a chance to get back to this. Anyway...

Thanks much for the suggestions! I'll be replacing those resistors when I next have time and space to work on this.

I've swapped the Denise with the one from my A500, and both exhibit the same issue. I left the plastic-cased Denise from the A500 in there, so that I would get the EHB mode. My original Denise didn't support EHB. heh.

[Ahle2]

BTW. check them all, R64-R67, R53-R56 and R68-R71.

It may also be something wrong with U5A, U6A or Denise.

[Ahle2]

It seems like the truth table of the green and blue 4 bit DACs are: ABCD 0000 = 0 0001 = 1 0000 = 0 0001 = 1 ... 1000 = 8 1001 = 9 1000 = 8 1001 = 9 B and C never changes. Check the resistors in the green and blue DAC ladders (R54, R55, R69, R70)

[EvilCensor]

As a keen A1000 owner I'd like to know if you resolved this issue?