Quick update: floppy and hd leds are working! Only power led is bad. I have to investigate that. But I'm not too worried, the CIA chip that deals with that is the most important one, and the machine is booting, so I'm confident this CIA is not bad. I hope it's a problem elsewhere.
The power LED should always work regardless, might be a cracked solder joint on the LED board or something simple. The circuit is literally 5V, a series resistor, and the dual package LED.
The _LED output from the CIA only makes the power LED slightly brighter, and also enables the 4kHz low pass audio filter.
And video is bad indeed, but I'll make the cxa2075m mod, that shall fix it, and give me a slightly better composite output.
If the RGB output is good, but there's a problem with the composite video output, that would suggest a problem with the composite encoder circuit, based around U12. The most common fault is bandpass filter or delay lines Z221/Z222 go open circuit as a result corrosion from leaked capacitor corrosion. These parts aren't available new, but the damaged ones can often be repaired, though it requires some tricky soldering. Some of my scanned handwritten notes on checking these parts (PAL) are
here. I don't have notes on the NTSC parts, though if you measure more than about 10-20 Ohms end-to-end, then one or more of the internal coils is open circuit.
If you're trying to view the PAL composite signal on a NTSC monitor, that would likely look bad as well. If you view a NTSC composite signal on a PAL monitor (1084S), the image will appear, but as monochrome. I don't know what to expect if you view a PAL signal on a NTSC monitor, the video standard is PAL in my part of the world.
By the way: is it easy to convert a PAL A1200 to NTSC? Without hacks? This one is PAL, but since I'm in Brazil, NTSC is a more compatible standard.
If you want correct NTSC composite video compatibility, it involves various changes to components in the composite encoder, and changing the crystal oscillator from 28.37512MHz to 28.63636MHz. It's a lot of messing around.
As you say, configuring the board to default to NTSC (fit R203, 0 Ohms) will work if you're using RGB video.
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