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View topic - Help fixing the Composite/Audio output.

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  • Joined: 24 Sep 2013
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Help fixing the Composite/Audio output.
Post Posted: Mon Mar 12, 2018 8:29 pm
I've decided to retake the task of fixing the composite video and analog audio outputs of my Master system. The audio is completly silent and the video is all garbled and TV can barely show it.

I've opened the console and other than general dirtyness it is the same way it was when I found it (pictures attached for this and all other issues). After that I've hooked up the outputs to the scope and the audio sits at a constant +450 mV output while the scope is unable co catch the sync pulse at all. Compared to the output of a working PS2 it doesn't even start to look like Composite video.

Any help or known issues with these issues?
circuit-board.jpg (373.16 KB)
Circuit board near the DIN connector.
circuit-board.jpg
good-composite-from-ps2.jpg (146.72 KB)
Good composite signal (PS2)
good-composite-from-ps2.jpg
bad-composite-from-mastersystem.jpg (142.1 KB)
Bad composite signal (SEGA)
bad-composite-from-mastersystem.jpg
audio-line.jpg (162.08 KB)
Audio line sitting at 450mV
audio-line.jpg
sms-composite-issues.zip (1.15 MB)
Video of how it looks on a TV.

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Post Posted: Mon Mar 12, 2018 8:39 pm
First question has to be, did you replace all the capacitors?
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Post Posted: Mon Mar 12, 2018 8:52 pm
The electrolytic ones didn't look 'bad' on the outside so I didn't, but I could give it a shot. Is it a common occurrence with the console?

Hope the replace all doesn't also affect the ceramic ones too :P
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Post Posted: Mon Mar 12, 2018 10:00 pm
Yes, electrolytics don't age well regardless of quality, and your errors look more analogue than digital to me.
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Post Posted: Sat Jul 14, 2018 1:37 pm
Found some time to replace all electrolythic caps, the result is the same. Maybe the video chip is actually dead?
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Post Posted: Tue Jul 17, 2018 2:57 am
NeonMan wrote
Found some time to replace all electrolythic caps, the result is the same. Maybe the video chip is actually dead?


Check the crystal connected to the VDP (marked "OSC"), it should be around 10.53 MHz or 52.693 MHz depending on your motherboard. If that seems good, verify the reset signal (goes to the VDP and Z80) isn't stuck low and check the composite sync coming out of the VDP directly for signs of life.

I'd also measure the 5V rail on the VDP and at a few chips around the board and verify you are getting good power all over.
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Post Posted: Wed Jul 18, 2018 3:07 pm
NeonMan wrote
Found some time to replace all electrolythic caps, the result is the same. Maybe the video chip is actually dead?


replace the video encoder chip.
CXA1145P

you can buy one online cheap...
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