OSSC only outputs blue
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I’m using the OSSC to convert a nonstandard “VGA” signal from a PC-98, it was working great until one day I flicked it on and only got the blue analog channel. I’ve tested the cable and the PC-98, the red and green signals are definitely making it to the OSSC, and the test screen shows the normal grayscale gradient, but anything from the PC-98 comes out in blue-scale. At this point I’ve narrowed the problem down to the OSSC, is there anything to be done for it, or is it toast? I would have bought a replacement by now, but I haven’t seen the v1.7 come back in stock for over a year now and I don’t know how well I can trust random 3rd party ebay clones.
Update: Just tried the hardware mod and updated to fw v1.03, still blue.
Unfortunately the PC-98 uses RGBHV, which I believe is only supported by the VGA-in. Since the signal out from the PC-98 is this weird 640×400 @ 24 kHz h-sync that nothing supports, the OSSC is the only thing I’ve found that can decode it into anything usable, so I don’t think I can find an adapter to use either. I’m worried the weird signal is what killed the board in the first place, even though it was working so well up until it broke. I can possibly replace the ADC chip, but I’ve haven’t hand-soldered much at this pitch. I guess I can give it a shot, it’s not like I’m in a rush to get these things running again, what with the language barrier.
Edit: Looks like I could maybe make a sync combiner to get an RGBs signal to play around with, I’ll still need to figure out how to adapt that to AV1 or AV2 though.
Looking at the datasheet for the video ADC. From here it looks like all the video inputs just go through the same circuit on this chip, so that decreases my confidence that just switching to a different input will have any effect. I might try seeing if maybe I can hook my wii up to V2 in and seeing what happens. That said, this chip doesn’t support anything like the signal from the PC-98, so idk what kind of black magic is going on to make it work, but that does lend weight to the signal being what busted the OSSC in the first place. If anyone has any insight on that, I’d be very interested. My OSSC shows 440-p 24.83kHz h-sync with 56.42Hz screen refresh.
Now that I’m looking at the BOM, I also wonder if the issue could be with the filter IC.
Probably time to break out the oscilloscope again and see what there is to see on these 2 ICs.
Edit: Pitch is too small to get probes on. Now that I’ve had a closer look at the board though, I don’t think I’m going to be able to replace the ADC without a hot air station, which will cost almost as much as just replacing the whole board outright. Not sure what to do, if the PC98 kills another board, I’m out another $200 and left without a lot of options for getting a picture onto a monitor.
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