Martin Roboscan 918 blowing main fuse

[sk8rsdad]

I am looking for help troubleshooting a Roboscan 918 that has started blowing the main fuse. If I need an expensive part then it is not worth repairing and it will get used for parts for the other 3. So the classic question when an old reliable is no longer reliable is do I repair or replace? I don't want to get into part swapping to narrow down the issue since I can't afford to lose the other 3 at this point in time and being a power problem, there's a good chance of damaging the parts from another unit.

When the fuse went, it generated enough heat to partially melt the fuse holder. After replacing the fuse, the lamp operated fine through a dozen lamp strikes but failed when I inadvertently lamped off and did a warm restrike. When it lamps on, there's a bright flickering flash from the fixture that lasts a couple of seconds before dimming down and warming up. The other units don't exhibit this behaviour

I suspect that the starter is staying engaged longer than it should. The next time I have it on the ground I'll give the fixture a search for visible damage. In the meantime, does anybody with more experience repairing this sort of gear want to make a guess at the probable cause and cure?

 

[TimMiller]

Is the flash from the lamp or some other part in the fixture? Is the ballast and transformer taps set to the right voltage and frequency. Typically the Ignitor will have to go through several cycles to strike a hot lamp compared to a cold one. What does the globe inside of the lamp look like? It should be clear to slightly frosted, if it is powder white or black the lamp is past it's life in terms of hours. Arc lamps do not burn out they just keep getting dimmer and they put more stress on the electronics of the fixture. Check the lamp pins and sockets for signs of arcing also make sure the Ignitor wires are tight, they do viberate loose causing all sorts of problems. Let us know what you find.

 

[sk8rsdad]

Good questions. All the Robos were relamped in May and have under 200 hrs of burn time. It is possible the transformer taps were changed by somebody but not very likely. More likely would be an issue with the new lamps. I will let you know what I find when I get over to the theatre on Wednesday and get a chance to pull the covers.

Murphy's Law is holding true since the misbehaving fixture is in the most awkward place right now, hanging on a batten that can't get within 3m of the stage deck due to a set wall, and can't be reached by lift because it is over a riser. It's a shame it couldn't have been one of the 2 sitting on the floor.

 

[sk8rsdad]

I got a chance to service the units. Other than the power cord and connection area which showed visible melting there is no sign of any damage elsewhere. The transformer and ballast taps are set correctly for 120V 60Hz operation and confirmed by measuring the transformer output voltage. The lamps are crystal clear with no signs of fogging which is no surprise given the number of running hours.

I replaced the damaged power cord and fuse and cycled the unit through an number of cold lamp ons and couldn't find anything obvious. Yet this is the 4th fuse in 2 months. The other units have never blown a fuse. I'm stumped.

 

[TimMiller]

If the power factor cap starts to go the unit will draw more amperage. If you have a capacitor tester test it and look for any signs that it may be failing. These typically do not fail catastrophically. i once dealt with a cyberlight that was doing the same thing. the problem was with the circuit that ran the power factor cap. After a bit of testing over the phone with lightparts i was able to make the repairs. Measure the resistance across both sides of the ballast and transformer compare the readings to another units or two because there may be little variation. Also don't forget to make sure your Ignitor connections are tight. Also on the top of the Ignitor it should be a fan color as they age they may start to turn dark brown. If you really get stumped I would say give them a call they have some good Martin techs. I may also have some 918 parts laying around.

 

[JD]

You might be over thinking this one. You had said the fuse holder itself was partially melted. Much like a lamp base, if the contacts in the holder are oxidized or compromised, the fuse holder may actually be the problem! Bad contacts will generate heat which may be popping the fuses. If they were popping instantly, then that would be a different story, but this one may simply be overheating the fuse.

 

[TimMiller]

Honestly I completely forgot about that, it is possible. Also make sure you are using the correct fuse it should be 6.3 amp for 220-240 v operation and 10 amp for 100-120v operation. Also per Martin they say the power factor caps should be replaced every 4-5 years.

 

[sk8rsdad]

Thanks. The PFC caps were replaced about 5 years ago when we acquired the Roboscans so maybe it's time to replace them again. I think JD is on to something with the heating. It may be that the cord connector is/was bad. It would explain a lot. Time to find a replacement connector and new PFC.

 

[lightman02]

Thanks. The PFC caps were replaced about 5 years ago when we acquired the Roboscans so maybe it's time to replace them again. I think JD is on to something with the heating. It may be that the cord connector is/was bad. It would explain a lot. Time to find a replacement connector and new PFC.

I had the same issue with a SS250 blowing it's main fuse and it turned out to be the PFC. Even if they are not that old they can still fail early, it's the most likely cause. In fact the fuse would only blow when I was using the dimmer flags a lot. It was strange but it was the PFC causing the problem.

 

[sk8rsdad]

The CPFC, IEC socket and power cord were replaced a week ago and so far so good.