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Chassis fire - HELP!


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  • Chassis fire - HELP!

    Hi guy's,

    I'm not back from hiatus. I just have a question. On my days off, my “B” had a chassis go up in flames. I've never seen this before & I was wondering if anyone could tell me what caused what.

    (82-70 - SS chassis - Omega-Tek MK- 70)
    The chassis was completely rebuilt last month. It wasn't rebuilt due to a problem. I'm going thru all the chassis because they haven't been serviced by someone that knew what they were doing since they left the factory.
    When I 1st tested the chassis, after the rebuild, the B.E. relay was sticking. I cleaned up the contacts but it didn't help, so I changed the relay.
    It functioned fine for about 1½ days. Then, no B.E. motor run. (Everything else functioning normally) While my “B” was troubleshooting the problem (he had his face pretty much in the chassis), the 2 varistors on the heat sink assy & 2 disc capacitors on the MK-70 started to release their smoke, then caught fire. The 2 caps on the MK-70 that fried were the ones directly below the “cycle from desk” jumper. According to the PC board layout that comes with the installation instructions, they are “M3” & “M4”.
    Every bit of solder on the heat sink assy melted – not just the solder at the varistors. All the power diodes on the heat sink assy check out OK with the meter. Nothing else in the chassis is visually bad or out of place.
    The B.E. relay, which was the last thing that was messed with, checks out OK. It's wired properly & shows no obvious signs of overheating.

    My question is… What precipitated the whole thing?

    Did the varistors fry the MK-70? Did the MK-70 fry the varistors or was it something else that fried them both?



  • #2
    Re: Chassis fire - HELP!

    I hope he did'nt take CRUD's advise and wash it down with a hose while you were out! [img]/content/btubb/images/%%GRAEMLIN_URL%%/eek.gif[/img]

    Charlie [img]/content/btubb/images/%%GRAEMLIN_URL%%/smile.gif[/img]
    Please buy MADE IN USA!


    • #3
      Re: Chassis fire - HELP!

      Smoke of that magnitude isn't seen often, and it takes a heck of a current to make it happen. Without seeing or testing it, my guess would be something like the primary and secondary windings of the T1 / T2 transformer bridged and let line voltage leak into the circuit, something fell into the front wireway and crossed a couple wires between signal voltage and line voltage, something that would let high-current/high voltage into the low-v control circuits.
      <span style="font-style: italic">Educatio est omnium efficacissima forma rebellionis</span>


      • #4
        Re: Chassis fire - HELP!

        This is what happens when the B.E. motor fries against the frame of the machine.
        If at first you don't succeed, try, try, again. Then quit. There's no use being a damn fool about it.&quot; -W.C.Fields


        • #5
          Re: Chassis fire - HELP!

          Last Chassis fire I had was on Super Bowl Sunday about 9 years ago.

          It wasn't pleasant.



          • #6
            Re: Chassis fire - HELP!

            Last summer I had a chassis fry just like you said. Heat sink just fired up, varasistors and diodes burnt up. Omega tech boards died.

            Turned out the sweep reverse switch in the control box fried, somehow sending a surge through the sweep contactor and the rest was history.

            I have since changed all sweep run and sweep reverse switches in the control boxes. Call me paranoid, but I did not want to buy anymore omega tech boards. Warranty doesn't cover fires. [img]/content/btubb/images/%%GRAEMLIN_URL%%/eek.gif[/img]



            • #7
              Re: Chassis fire - HELP!

              The pitlight/interlock terminals could have shorted on the M-relay.
              If CB3 on the chassis didn't trip the short probably went through the BE relay coil and fried it to.
              I'm just taking potshots. I dont have omegas.


              • #8
                Re: Chassis fire - HELP!

                Faulty Heat Sink? Too much heat could have started a natural combustion.

                Well thats just like your opinion man...


                • #9
                  Re: Chassis fire - HELP!

                  Thanks guys,

                  I was pretty sure it was high voltage in the low voltage circuits but I didn't know where to start looking. I'll head off in the direction you've pointed me in &amp; I'll let you know what I find.

                  Gotta love this site. You can't get this kind of input just anywhere!

                  Thanks again



                  • #10
                    Re: Chassis fire - HELP!

                    Last time I had a smoker like that, some complete $h!thead (namely me ) left a punch sitting up by the chassis, during leagues, the machine vibration made it roll &amp; fall into the wireway where there's no capping under the chassis, and shorted the TS strips.

                    DOH! [img]/content/btubb/images/%%GRAEMLIN_URL%%/eek.gif[/img]

                    Another thought... the problem with the ole' SS chassis is that the original transformers, rectifiers and filters are just too dammed STRONG! If they feed 24VAC under normal conditions, you get a surge, and instead of blowing out, they just continue on their merry way, except that they are now operating under higher power, and feeding 50VAC into the circuits instead. Sometimes they're a little too heavy-duty for their own good...
                    <span style="font-style: italic">Educatio est omnium efficacissima forma rebellionis</span>


                    • #11
                      Re: Chassis fire - HELP!

                      Judging by the photo, it looks like the C1 socket gave up &amp; caused a major short in the chassis. I have seen quite a few that were similer in appearance to the one in the pix. Most of the ones I have seen were in the B.E. wiring part of the socket (or plug end). Since the connectors are made of bakelite, they start to break down when they get hot due to bad pins, then the rest just keeps adding up until *poof* fireworks!

                      Good luck...Jon [img]/content/btubb/images/%%GRAEMLIN_URL%%/usflag.jpg[/img]
                      I've had enough of hope & chains.


                      • #12
                        Re: Chassis fire - HELP!

                        fire !

                        Once i saw a pinspotter stop with the table in the lowest position just above the pindeck. I walked around to get behind the lanes and i noticed a black smoke clowd coming out of the chasis. Moving closer i encountered a terrible smell, yikes. All this was coused by the spotting relais which was melting. Tini flames came out of it. So check that too [img]/content/btubb/images/%%GRAEMLIN_URL%%/frown.gif[/img]


                        • #13
                          Re: Chassis fire - HELP!

                          The last time there was coming smoke out of my chassis was when I left a cigarette too long in there....I did forget the yearly empty job.

                          So it goes.


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