Technic_Lee Posted January 24, 2015 Share Posted January 24, 2015 One Mac 250 Entour is always blowing out its 6.3A fuse almost as soon as I replace it. I presume it's Short-Circuiting somewhere, but has anyone had this problem before? I have numerous Mac 250 Entours onboard a cruise ship, and I've just taken the position of Light Tech. I'd like to know a likely solution before I de-rig. It's a hard job de-rigging and must be completed quickly in my theatre. Thank you in advance. Link to comment Share on other sites More sharing options...
timmeh2 Posted January 25, 2015 Share Posted January 25, 2015 Hi First of all - stop sticking new fuses into it unless you fancy setting fire to something. It's usually a big deal and you'll have to dismantle and inspect the unit, and it's not something you can do whilst its up in the air. You might be lucky and find some frayed insulation or unlucky and it could be a PSU or MCB fault. If you haven't got a spare unit or parts handy, accept the fact that you're going to be without it for a while. If that means relighting then so be it. I'm sure your Production Manager will be supportive. If he isn't, remind him that safety to the ship is the first priority and trying to use a malfunctioning piece of equipment is a definite no-no. If it's beyond your skills of expertise, be honest and get the thing landed and repaired, or arrange for a Martin rep or suitably-experienced technician to come onboard during a turnaround day and get it fixed. No one will have a go at you for holding your hands up, they will get vexed if you try to cover up the issue or make it worse by trying to fix it yourself. Sorry if this sounds a bit harsh but this is the real world. Operating a rig on a ship is a whole different ballgame to being on land. If you're doing something risky then the consequences of having an accident at sea are far more deadly. You can't just phone for an ambulance when things go wrong. All the bestTimmeh Link to comment Share on other sites More sharing options...
Ken Coker Posted January 25, 2015 Share Posted January 25, 2015 You are using time-delay and not quick-blow aren't you? But as the above poster points out, fuses blow for a reason. KC Link to comment Share on other sites More sharing options...
Technic_Lee Posted January 26, 2015 Author Share Posted January 26, 2015 Thank you for the indepth response over a rather vague issue. It's much appreciated Link to comment Share on other sites More sharing options...
Jivemaster Posted January 26, 2015 Share Posted January 26, 2015 Have you actually read the label (stamping) on the fuses. I know of one major incident that was resolved by taking the box of 63A fuses out of the space labelled 900A in a stores. Link to comment Share on other sites More sharing options...
Technic_Lee Posted January 26, 2015 Author Share Posted January 26, 2015 Absolutely. I always check. Especially since the work space is handed over to different techs every few months, you can never be too sure. I've now check the fixture all over, and there are no obvious flaws. So I'm going to start replacing parts with spares. The last fuse to go was in a bad way. I will have it down for as long as the repair takes. If anyone has had a similar problem, or suspects a likely cause (though no burning, fraying, or shorting seems apparent) I'd like to know. Thanks Link to comment Share on other sites More sharing options...
Don Allen Posted January 26, 2015 Share Posted January 26, 2015 When a fuse blows, I look at it to interpret the way it went. (Glass fuses ) If it has just parted in the centre, it could be old age stress, so I can try a new one to see what happens. If it has disappeared, there is an overload and I troubleshoot with that in mind, unless it was the wrong rating fuse i.e. fast blow in a slow blow holder. If the inside goes black due to the high rupture, I know there is a dead short, usually in the power supply, so I tag the unit out of service and open it up to repair. Link to comment Share on other sites More sharing options...
bigclive Posted January 27, 2015 Share Posted January 27, 2015 Keeping in mind that for mains voltage the fuse should be a ceramic one rated to break a high fault current. The reason glass ones go "metallic" inside under severe fault conditions is because they turned into an arc-lamp momentarily, and while they were arcing the current was still flowing and destroying stuff. Typical 20mm glass fuses are only rated to break a fault current of about 35A while the 20mm ceramic ones with internal quenching agent can break a fault current of around 1500A. I've had seriously damaged PCBs for repair that had been fitted with glass fuses that had failed with such force that the fuse had exploded and the plasma erupting from it had caused a chain reaction along several others in its vicinity. Link to comment Share on other sites More sharing options...
darkwarior Posted January 27, 2015 Share Posted January 27, 2015 Are the Mac 250s being used in at 220 (or 240, I forget the setting options on the slider), or at 110? Here in the US, I typically run mine at 208v (220v setting), but once in a while I need to set them to 110v for an event. Forgetting to switch it back from 110v to 220v will result in blowing out the fuse and harming the mainboard. Once that has happened, the mainboard is dead until it can be replaced or fixed. This sounds like your mainboard has been damaged from an improper voltage setting or surge/spike and requires replacing the mainboard. Link to comment Share on other sites More sharing options...
KevinE Posted January 27, 2015 Share Posted January 27, 2015 how long does it work for, before it blows the fuse? I would check wiring loom, ignitor, lamp & holder, PFC cap and ballast,in that order. And once a new fuse has gone, dont feed it fuses any more. If the lamp cable in the loom has gone down you risk flashing ignition voltage to the motor loom then it's bye bye main board Link to comment Share on other sites More sharing options...
gafferted Posted January 27, 2015 Share Posted January 27, 2015 I'm not familiar with these but do they have a mains filter in them? I had a spate of my old Robe/Futurelight units doing the same thing, which was cured by replacing the mains filters with these Link to comment Share on other sites More sharing options...
Technic_Lee Posted January 28, 2015 Author Share Posted January 28, 2015 My Mac 250s are running on 110v and during testing after I inspected it, it ran for 15 mins before blowing, the fuse must have arced as it had blackened, cracked and has molten metal on the outside.After changing the bulb it ran on test for a full hour with no problems. A friend working for Martin suggested it could also be a fault with the arm motor, so if it fails again in testing, I'll check that. Link to comment Share on other sites More sharing options...
Tow Posted January 28, 2015 Share Posted January 28, 2015 the fuse must have arced as it had blackened, cracked and has molten metal on the outside. That would indicate a direct short occurred. Was the head moving or just sitting there? It does not sound like a motor problem, the motors are feed through stepper drivers chips, a faulty motor or its wiring would tend to blow the driver chip and/or sense resistors and then the fuse. On replacing on the fuse it would blow again (when switched on) or the motor in question not run, depending on how the driver chip blew. In you case the fixture operated correctly for a while. As Kevin says: I would check wiring loom, ignitor, lamp & holder, PFC cap and ballast,in that order. Link to comment Share on other sites More sharing options...
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