CD32 Missing Color

[EvilDragon]

Hi,

I've got a CD32 which I just cleaned and replaced the capacitors.
It's rock stable, everything runs fine - except for that it's missing color, both on SVideo and Composite video output.

I already replaced the CXA 1145 with a different one (from an A600), but that didn't change anything.
It could theoretically be that the CXA 1145 in the A600 had the same defect - but that would be a weird coincidence.

Does anyone know how to troubleshoot that?
I already tested pins 21 - 23 on the CXA 1145 (which would be RGB Output), and all three have signals, so I guess that means the input into the CXA 1145 should be fine.

But how does it work from there?

If I understand correctly, the encoder takes RGB in and converts it to Luma / Chroma Out (Pin 15 and 16). From there, it goes to the SVideo output (through a few components) and back into the encoder chip, which converts it to Composite video.

Is that right?

If yes, then that means something between the encoder chip output and the SVideo port is defective (or the encoder chroma out itself).

How should I continue from there? Should there be any color if I connect Luma / Chroma out from the encoder chip directly to the SVideo port (without the components inbetween) or are these needed for a proper signal?

Thanks in advance for any help.

[supaduper]

You will find that some component in the delay line has gone bad, and some of these components are no longer available, the best way to do it now is to replace the CXA1145 with the CXA2075 which has the delay line built into the chip and you can forget about the Delay line on the motherboard, it works with the CD32 as well

link here on how to
[ Show youtube player ]

[EvilDragon]

Thanks a lot! Does anyone know which resistors I need to remove on the CD32?

[supaduper]

Originally Posted by EvilDragon

Thanks a lot! Does anyone know which resistors I need to remove on the CD32?

You do not need to remove the old components

[EvilDragon]

Okay... I'm still not getting there, unfortunately.

Here's what I did so far:

* Replaced the encoder with a g
* Removed C221, C222, R221, R222, R223, R225
* Replaced U36

The issue is still the same:
Distorted color on SVideo out and no color on Composite out (rocksteady image otherwise).

My guess is that the composite is B/W because the Color signal is defective and the Encoder can't encode it into the composite signal properly.

This is how it looks like:



Now, I did a few tests trying to figure out where the problem (video noise?) occurs.

As a test, I removed C211A, B and C. This disables the RGB input into the encoder - so it shouldn't receive any signal (except for the csync which comes directly from Alice). So it should make a clean black signal.

And yes, the signal is black - however, it also has the reddish distorted color on top!

--> It seems to not be related to the RGB input signal.

I also connected the Y/C directly to the encoder chip to make sure it's not c component that's between the Encoder chip and the Y/C connector.
The same result.

So as conclusion:

* A new encoder chip creates a reddish noisy chroma signal and a b/w signal on composite video out.

* It's not the RGB input, as it also happens when I disconnect the RGB Input


What could it be? Could a bad CSync cause such issues?
Could VCC cause such noise? (I've measured the voltage and it's fine (4.96V), but maybe it's noisy?)

Or could any other components on the boards where the encoder chip is connected to cause such issues?

Any ideas what this could be?

Thanks a lot