Amiga CD32 No Composite Signal

[quiet1]

Hey All,

I have recently purchased a 'faulty' CD32 which I am now in the last stages of restoring.

I recapped and cleaned up the board, a lot of leakage unfortunately. (Thankfully I also became aware of the 2 reversed caps before I started).

After the re-cap I was able to test it through S-Video and its working fine. Even the CD drive is reading discs correctly.

One issue is that I am just not getting composite signal, the schematics are not that complicated so I don't understand what I'm missing. I've tested using a composite port directly on a screen and also through a RetroTink 2X Pro.

I have tried:

• Isolating the composite line by removing the RF capacitor and resistor
• Replacing the encoder (CXA1145)
• Removed the RCA jack

The CXA1145 encoder (U12) is giving 2.2v from the CV_OUT pin (20), whats weird is that I can have voltage at the RCA jack until I wire it up to test then it seems to give nothing: 0v and doesn't seem to charge back up to 2v unless I leave it powered off for a while and switch it back on.

I was going crazy thinking I was chasing a short for ages.. but I think this may be normal ?

On some further testing I can get a signal if I connect LUMA to the RCA but then S-Video quality is reduced.

Does 2v seems correct for a composite signal? Any ideas what could be missing?

I have a feeling that some via got corroded or something, but I dunno where to look at this stage

I know all this is only for crappy composite, and I've already spent too many hours trying to figure it out but I want to get it back together as a fully working CD32 machine one and for all..

Any suggestions on what to look out for? it would be much appreciated!

Thanks!

[Mick]

C-Sync issue? check continuity between pin 80 of Alice and pin 10 of the encoder.

edit: then again, it must be working if you're getting a sync on luma.

edit: Looking at the CXA1145 datasheet I think the delay line might be the problem? or maybe something with C459/R459/C460/R222/R224 or the VVref voltage.

If it's a faulty delay line then the easiest thing to do is to do is replace the CXA1145 with a Rohm BH7236, remove all of the delay line, band pass filter & iref/vref parts, you'll need to remove C214 as well. Then put a 22pf capacitor in C222 and a 68uH inductor in R223. Additionally, for the CD32 you'll need to connect the Chroma and Luma outputs directly to C281/C282 and remove all of the stuff that's inbetween. Rohm recommends C281 to be 220uF, C282 to be 0.047uF and R283/R285 to be 75 ohm but it might be fine stock.

[supaduper]

As mentioned above as you get S-Video but no Composite then I will say the Delay line circuit is the fault so just replace the CXA1145 with a CXA2075M encoder as has the delay line built into it

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