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Thread: Pics: Sigma Raijin video board rework

  1. #1
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    Pics: Sigma Raijin video board rework

    I bought RAZO's broken Sigma Raijin, hoping that the video board was repairable. It is, in the barest sense. A few traces were vaporized, the circuit board was cooked clean through in one place, and every IC was dead. Luckily, it's a pretty simple board, with all standard parts, and essentially all of them are labeled in silkscreen. With a knockoff Hakko and 1997's most affordable oscilloscope, I got to work.


    This is what the video board looked like to begin with:
    video_before.jpg

    I clipped off the obviously fried parts and took the pins out with solder wick.
    video_cleanup.jpg

    I desoldered all the ICs too. I replaced the ICs with sockets, and replaced any questionable passives too.
    video_repaired.jpg

    I don't have an LM1881N or a CXA1645 on hand, but I replaced the standard logic parts, and saw that the subcarrier oscillator (CXA1645 pin 6) and asynchronous autofire (connector pin 4) both worked.

    subcarrier.jpgautofire.jpg

    When I get the video parts in, I'll post pictures of it (hopefully) working.
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    Good luck, hope you get it working!
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    Wow, this is an interesting breakdown Spam, thanks, and I hope you get positive results here.

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    Nice work man hope you get it up and running again.
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    Holy crap! Was this thing struck by lightning? Those cooked resistors really left a mark. Great job on restoring it, though.

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    Quote Originally Posted by Morden View Post
    Holy crap! Was this thing struck by lightning? Those cooked resistors really left a mark. Great job on restoring it, though.

    Yea, Something like that.


    @Spam

    Can't wait to see it up and Running. I got faith in you bro.

    By the way, the harness and av cable was shipped out on Wednesday, so you should be getting it soon.
    Last edited by RAZO; 11-12-2017 at 08:35 AM.

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    Your repair is looking great.
    Goodluck and a nice score if you get it repaired.

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    Great report, good luck and please keep us posted!!
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    Loving those photo progress and detailed write up - hoping to see this beast back in business

  10. #10
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    Really nice work and great to see the breakdown of the process.

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    Looking good. It’s always nice to see things get fixed rather then thrown in the scrap bin.

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    Is the PCB only superficially scorched? I thought scorch marks on a PCB can be conductive.

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    Quote Originally Posted by DanAdamKOF View Post
    Is the PCB only superficially scorched? I thought scorch marks on a PCB can be conductive.
    At high voltages, and with the soot from charring still covering the PCB ... maybe. This board, even though it still has a mark, has been cleaned, and even if it wasn't, the voltage is nowhere near enough to cause problems.

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    I checked for shorts between the components I replaced, and everything looked reasonable. I checked the resistance of the board around the soot and it appears to be nonconductive (>2Mohm). Thanks for the heads-up.

    I've got the LM1881 incoming from Digi-Key and some CXA2075 (Sony's replacement for the CXA1645, and apparently pin-compatible) coming from China.

    The power supply appears to be fine - output seems stable, and the manufacturer's web site indicates that it's protected against 1.5kV faults between inputs/outputs (so, anything that was caused by an AC line short shouldn't kill it, right?).
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    The NTSC encoder chips came in from China. They're SOIC packages, though, instead of DIP like the old one. Additionally, the only DIP adapters that Digi-Key stocks are for .3" row spacing, rather than .4". So, I made this rather clumsy adapter out of some sockets:
    goofy.jpg

    I then soldered the new, surface-mount part to it with hot air.

    cxainstalled.jpg

    I attached the cables and powered it on with a game attached. I had sound but no video. I checked around the pins on the CXA chip, to make sure my soldering was good, and found that my external ground (on the edge connector) wasn't continuous with any other ground.

    I poked around and found that a ground trace on the edge connector board was totally annihilated.
    ground_pop.jpg

    I fixed that.

    ground_fix.jpg

    It still didn't work (power and sound, but no video), so I poked around on the video encoder chip a little more. I saw that the RGB input was fine, on the right pins, and as specified in the datasheet. The datasheet mentioned internal RGB buffers that should output the plain RGB, again, on some other pins - which showed only a 15KHz sawtooth. I replaced the chip with another (good thing I bought the 10-pack), and it worked.

    werkin.jpg

    No idea if the chip was bad from the supplier, or if I fried it with the hot air - I did the second one with an iron.

    I also got rid of the janky socket-stack - if I solder the pin headers to the very edge of the pads on the Proto-Advantage board, it works for .4".

    400mil.jpg

    Last but not least, I used some heat-shrink tube to mitigate the design problem which caused this whole mess.

    tube.jpg

    Bonus: Fuck that stupid proprietary power cord.

    plug.jpg
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    Good job bro.

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    Incredible work! Not many of us here have the know-how to take on a repair like this. This was a great read.

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    Great work. How much did it cost to repair the unit?
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    Awesome job man. Very clean work, like the new power cord /socket.
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    Quote Originally Posted by daskrabs View Post
    Great work. How much did it cost to repair the unit?
    I couldn't tell you exactly - most of the parts, I got from a friend who happens to be an electronics engineer. The video encoders were 10 for $12 on eBay.

    The cost is mostly time and equipment. I'd say it's easily worth it, if you're into arcade games at all, to pick up an old oscilloscope.
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    Awesome, thanks a lot for sharing! Love when things get repaired!
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