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Sega Blast Cities

Discussion in 'Retro & Arcade Worklogs' started by mR_CaESaR, Oct 6, 2020.

  1. qwertylesh

    qwertylesh Member

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    What part fails to dim a tube? Is it the electron gun or something else, maybe repairable?

    Edit: derp its the full yoke right?
     
  2. Sledge

    Sledge Member

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    I've got some sort of 29" TV somewhere here i think... not sure if suitable or not?
    But Adelaide/Murray Bridge
     
  3. OP
    OP
    mR_CaESaR

    mR_CaESaR Member

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    I don't know the science behind it all, but this was the commentary I got from Joey

    So it looks like my "barium coating" has mostly been burnt off

    Thanks for the offer, do you have access to the label on the back of the tube and/or the model of the tv?

    If it fits, then I'm sure I can I do a yoke swap and get bill to pick it up. I'm still trying to see if there are local options but definitely appreciate it.

    I will get this back working one day - without converting to LCD! :D :D
     
    Sledge likes this.
  4. OP
    OP
    mR_CaESaR

    mR_CaESaR Member

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    Shortly after posting this, I was sent a message by a friend to try a Panasonic TC-68GS71A for a consumer tube swap. Whilst not 100% perfect, he previously used it on a tube swap for the blast city and yielded acceptable results. I was able to purchase the TV from FB market place and picked it up around early December.

    Here comes the most daunting task I've ever completed in this hobby! Yoke and Tube swap with a consumer TV :D

    [​IMG]

    After a solid few days worth of reading, watching youtube vids and general research, it was time to disassemble! The first thing I noticed was, this tube was CLEAN!! (compared to any arcade tube - but that's expected given the totally different environments they were in)

    [​IMG]

    Tube is an M68KTY167X

    [​IMG]

    upload_2022-1-6_10-28-7.png

    Disassembly wasn't too bad, I had to use the frame screw to discharge as there's no metal frame like a normal arcade setup. Before you know it, the yoke was on and the chassis was installed!

    [​IMG]

    One thing that would've caught me out hadn't I been told, is that the convergence rings for the tube is best kept and used as the convergence rings - I would've disposed of the rings and used the one from the old tube to match the 2931!

    First major test - turn her on and hope nothing explodes, shorts or burns! *fingers crossed*

    She's turned on without any breaks! Popped a test pattern to first see how the purity is to determine what I needed to do with the yoke. So much discolouration so I needed to start mucking around with the yoke location :o

    [​IMG]

    Safety first before touching the yoke and rings live! :D

    [​IMG]

    This was the best I could get after a solid couple of hours s**tting myself moving the yoke and convergence rings whilst the monitor was on - I decided to call it a day and come back at a later time

    [​IMG]

    The last couple of days have been spent on trying to do fitment testing with the original frame, used a number of different ways to space out the monitor with the frame as the rabbit ears didn't have the same spacing

    [​IMG]

    With the spacing I used, the fitment ended up like this

    [​IMG]

    Red denotes there's no more space on the corners to push forward, yellow has a bit of a gap and green has a larger gap than the yellow

    The green gap

    [​IMG]

    The yellow gap

    [​IMG]

    I think once it's turned on and I'm actually playing the gap wont' be so bad and tolerable

    [​IMG]

    It's not a perfect fit... But it'll suffice for now.. 90% fit and working bright tube is better than 100% fit and unplayable :D

    After some more chassis tweaking I couldn't get the geometry perfect (well who can tbh? :D - especially on a donor tube). I have this bowing across all edges (drawing of lines are exaggerated, but it's there)

    [​IMG]

    Tried to straighten it up with some magnets, but I just couldn't get it straight, so I've just increased the h and v size to try and hide the imperfections, it will suffice until I come across an original tube (if it ever happens).

    Now the monitor looks like this - which I will say looks MUCH better than what I started with and what the tired tube looked like.

    [​IMG]

    [​IMG]

    [​IMG]



    I dare say 15khz is done! I will do the same process for 31khz and hope I can get it to somewhat look like the 15khz one as I'm hoping to use this cab for Monkey Ball :)
     
    Pierre32, flain, ShaggyMoose and 3 others like this.
  5. qwertylesh

    qwertylesh Member

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    mate that's incredible work!!!!
     
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  6. OP
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    mR_CaESaR

    mR_CaESaR Member

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    Thanks man, definitely a daunting process and I was sweating bullets all the way through the whole way, but the knowledge and experience gained is irreplaceable
     
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    mR_CaESaR

    mR_CaESaR Member

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    Here it is folks, she's back in business and the cab is playable again!

    [​IMG]
     
    Last edited: Jan 8, 2022
    Pierre32, Trizae, adz and 3 others like this.
  8. OP
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    mR_CaESaR

    mR_CaESaR Member

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    For those that remember this post.. I got a nasty little shock the first time I powered on this cab. I thought it was due to the switch, but I've since received another shock or two when I tried adjusting values through the remote board and I've taken a reading on the earth line and the metal plate only to see this value :o

    [​IMG]

    172V AC!!! No wonder why it bloody hurt!

    The same reading, but with the power off at the switch on the front of the cab (PSU is still getting AC from the back with the switch in its on state)

    [​IMG]

    73v is when the cab is powered on without the chassis plugged in

    [​IMG]

    Confirmed that 107v is going into the monitor which explains why I haven't blown up anything

    [​IMG]

    Now it's a process of elimination and try to determine where this leak is.

    Fun and games I tell you! (#saidnooneever)
     
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  9. flain

    flain Member

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    Yikes! You probably know this already but possibly somewhere ground and neutral wires have been swapped.
     
  10. OP
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    mR_CaESaR

    mR_CaESaR Member

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    Trying to find it is the hard part. I haven't really done much since except for removing the internal tranny which now makes it 50v instead of 172/180v AC.

    So there's still a HOT touching the ground somewhere
     
  11. flain

    flain Member

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  12. OP
    OP
    mR_CaESaR

    mR_CaESaR Member

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    Yeah seen that. Exact same transformer. He had about 27v in the end, I have about 50v.

    I've asked multiple folks I know that also have a blast and they all get 0v (which is what I expect for anything metal)
     
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  13. OP
    OP
    mR_CaESaR

    mR_CaESaR Member

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    So I've spent some significant time on this - fortunately, I didn't get zapped along the way!

    After reading the thread on Aussie Arcade - https://www.aussiearcade.com/topic/72785-sega-blast-city-abnormal-voltage-on-signal-ground-and-more/, I decided to take away my internal tx out of the picture just like the OP did. I simply tuned my 220v cab into a 100v cab and used my existing step down tx that my other blast is using - after probing, I had about 50-55V!

    I probed the same areas on my other blast city and it too yielded 50-55v on the metal plate. I've been using that cab for almost a year and never felt a shock, so I've never really looked into it that much. Back to the troublesome blast...

    Either way, I knew that I had a win already since I went from 172-180V down to 55V! I still didn't have the balls to touch the metal plate yet until I got it a little lower..

    Spent a good chunk of the weekend taking readings and special shout out to tiff_lee for pretty much helping with the troubleshooting

    Took the following measurements - probe points are ground pin on the control panel and P1 start pin unless otherwise noted

    • 56 pin (CN10) unplugged in off state (front switch) - dropped to 3v
    • 56 pin (CN10) unplugged in on state (front switch) - went to 9v
    • CN1 unplugged - no difference
    • With CN1 and CN2 unplugged in off state (front switch) - still reading around 3.9v
    • With CN1 and CN2 unplugged in on state (front switch) - went to 5.9v
    • With CN1 and CN2 plugged in, probed ground and a pin in CN10 - read 60v
    • Measured the pins on CN1 connector - every single pin showed 62v
    • Measured the resistance of ground and the metal enclosure of the PSU - was at 0 ohms
    So it was pretty clear that CN1 was the culprit, but wasn't sure why. The next step to take was to remove the common denominator between the two cabs - the external tx!

    I rigged up another tx I had and wired it up to the same place as the original tx

    [​IMG]

    Upon first power up, probing the same points as I previously have been, I'm seeing with a pretty low number! YES!!!!

    [​IMG]

    Did some more testing and probed the frame of the monitor which would essentially be the same as the metal plate since it gets mounted on it.. I get an 8v reading!

    [​IMG]

    Looks like I can definitely close this issue off and thank f**k for that! I will try grounding the internal tx to see if it lowers the voltage even more but tiff_lee mentioned that he didn't see a gain on his and his blast hovers in the 8-10v mark too.

    The only thing left really for this blast is trying to source an original tube!

    But for now, I will stick my tongue on that metal plate shock free! :D :D
     
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  14. badmofo

    badmofo Member

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    Great work! Nothing takes the fun out of your gaming experience like an epic zap.
     
  15. OP
    OP
    mR_CaESaR

    mR_CaESaR Member

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    I'm just too much of a stubborn b*$tard :D
     

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