Astro City monitor nanao ms8 no blue signal

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    • Astro City monitor nanao ms8 no blue signal

      Hi my friends,

      I recently got my first candy cab, a sega astro city, and i have been working on restore it, mostly aesthetically.
      The thing is when powering the cab (as the title says) im not getting blue signal on the monitor.
      Can anyone give some advice on how to proceed? can be the harness, a solder point in the chassis, a lose cable etc,
      Can anyone point me some directions on what, how and where to try to test first to fix this issue?



      Thanks my friends in advance :)
      Stand tall and shake the heavens
    • I agree first start with the basics of adjustments. After that A missing colour not show on Mon will usually be one of these type of things:

      - issue with the game board not outputting the colour
      - issue with the wiring from the game board to the Mon chassis
      - cold solder joints at the video input section of the Mon chassis
      - video processing IC on the Mon chassis
      - Colour drive transistor on the Mon neckboard
      - bad trim pot
      - cold solder joint on the CRT neck socket where connects to tube
      - bad cathode in tube itself


      Those are most likely but not complete list. All are fairly easy to test. If you have oscilloscope will drastically reduce your troubleshooting time for the blue signal. If not then start by breaking down to smaller sections (ie is it game board, is it wiring, is it Mon). If you see it's Mon then you break it down father, is it on tube or is it chassis issue (can ground blue cathode to check tube). From there just keep narrowing down etc. Video circuits are nice to test because there is literally 3 identical circuits and 2 of yours are working. Cab easy change parts and inputs/outputs around to verify issues and components.
    • brad808 wrote:

      - issue with the game board not outputting the colour
      - issue with the wiring from the game board to the Mon chassis
      - cold solder joints at the video input section of the Mon chassis
      - video processing IC on the Mon chassis
      - Colour drive transistor on the Mon neckboard
      - bad trim pot
      - cold solder joint on the CRT neck socket where connects to tube
      - bad cathode in tube itself

      So far, this is the progress:

      - issue with the game board not outputting the colour
      - issue with the wiring from the game board to the Mon chassis following the blue cable from the harness to the chassis makes connectivity
      - cold solder joints at the video input section of the Mon chassis
      - video processing IC on the Mon chassis have to double check but at least the pins seems fine and pass continuity test
      - Colour drive transistor on the Mon neckboard
      - bad trim pot tested fine with multimeter
      - cold solder joint on the CRT neck socket where connects to tube
      - bad cathode in tube itself tested blue pin to ground and blue appeared for a sec.

      So far i have spotted this issue:







      First pin leg from bottom to top seems disconnected on purpose by design but second pin seems corroded and broken.

      The datasheet for chip HA11423 says its a Color TV Deflection Signal Processor




      Seems resistance soldered over patched trace.
      Stand tall and shake the heavens

      The post was edited 5 times, last by MostroVeneno ().

    • That ic is nothing to do with your colour display. That is sync and drive processing.


      Do you know how to check transistors? Very common problem on all Mons is the colour drive transistors on neck board. See three mini transistors probably on heatsink? One red, one green, one blue. That is a good place to check since so common of a problem. If you don't know how to check transistor you can simply switch R or G with the B one. Then see if your problem moves to r or G. If it does then you know part is faulty.