Whizzzy Posted November 2, 2009 Share Posted November 2, 2009 Hi, As a project for the winter nights I am currently rebuilding a pair of Clay Paky Stage Color 1200 fixtures. Yesterday I reached the point where one of the fixtures was lamped up for the first time and have encountered problems. During the rebuild I have been switching the unit on and off in order to check the operation of the filters, iris, pan and tilt stepper motors and each time the unit was powered up there was a very brief arcing sound which I presumed to be the striking voltage for the lamp. On this basis I have assumed that the electronic ballast for the lamp is working ok. When fitting a new lamp yesterday I switched the unit on but this time didn’t hear the arcing sound and the lamp didn’t turn on. I then sent a re-strike command via the relative DMX channel hoping that this would bring the lamp into action, this time I did hear the brief arcing sound so assumed that the strike voltage had been applied to the lamp. Nothing happened so again after a short while I repeated the process. After another minute or so it was clear that the lamp was not going to ignite so I switched the unit off. On re-examining the lamp I saw it had gone completely black inside which now raises the question if the lamp was a defective from the outset or if there is a problem within the fixture that could have caused this. I had purposely chosen a known brand, Osram, as I had read varying reports in BR about the quality of the cheaper Taiwan imports. I have also searched the BR and Googled generally and can only find reports relating to HMI lamps going black at the end of their life which shouldn’t be the case in this instance (in theory). At this stage I am reluctant to put the lamp back in the unit for fear that it could explode and I don’t want to go and buy a new lamp and fit it if the same is going to occur. So can anyone give me advice if this problem with the lamp could be caused by a fault in the fixture or if it could be related to a quality problem in the lamp itself? Many Thanks Link to comment Share on other sites More sharing options...
KevinE Posted November 2, 2009 Share Posted November 2, 2009 I suppose it's possibly you've just been unlucky and got a duff lamp, it can sometimes happen; it happened to me with a Philips and it was replaced under warranty. During the rebuild I have been switching the unit on and off in order to check the operation of the filters, iris, pan and tilt stepper motors and each time the unit was powered up there was a very brief arcing sound which I presumed to be the striking voltage for the lamp Never turn a discharge light on without a lamp fitted, this is a good way to damage the ballast, ignitor, lampholder or even zap the control electronics. If you want to fault-find without a lamp, make sure the lamp-on command can never occur, or try to disable it. Link to comment Share on other sites More sharing options...
Mr Steve Posted November 2, 2009 Share Posted November 2, 2009 Never turn a discharge light on without a lamp fitted...Is there a way to work on fixtures which have no remote lamp on/off control? I've worked on discharge units before with the lamp removed but didn't realise this was bad! Link to comment Share on other sites More sharing options...
csg Posted November 2, 2009 Share Posted November 2, 2009 yes, remove the fuse from the lamp circuit, the vast majority of fixtures have the lamp circuit fused seperately. It is some years since I last worked on a clay paky fixture like this, so my memory is a little patchy, but iim sure there is fuse protection on the lamp circuit. In this case, it is possible that the black colour of the arc tube is due to poor ignition voltage, and the lamp striking briefly. It is typical of lamps which have been struck briefly to look black due to the deposition of the hailides present in the arc tube on the glass, rather than the vaporisation that whould happen with a full warm up cycle, and the proper condensation which would happen with a full cool down cycle Even after a full life, it is unusual to see blackend HMI arc tubes - more commonly the arc tube will be opaque white / pale yellow If you could hear arcing out on start up without a lamp being fitted it suggests that the ignition voltage might be leaking to ground somewere - it is worth taking a good look at the HT leads which run from the ignitor to the lamp holder. They do suffer a bit in clay paky scans, due partly to UV aging, and obviosly heat. Years ago when I used stage scans and superscan zooms a great deal, the HT lamp leads used to require replacement from time to time. Ignitors did also fail, generally becoming weak and fussy only starting newish lamps prior to failing completely. Either way, repeated brief start up of the lamp circuit with or without a lamp is a great way to damage both the idnitor and lamp, so not advisable. Finally. I am yet to find a faulty double ended osram hmi lamp, and I still get through a fair few of these every year in some of my moving heads. If the lamp looked normal when fitted, it is highly likely it was damaged by brief or incomplete ignition. You may find that it starts up fine in a fixture with a good lamp circuit, and if left to warm up and coll down properly, it will look normal again when cool. good luck... Link to comment Share on other sites More sharing options...
KevinE Posted November 2, 2009 Share Posted November 2, 2009 You may find that it starts up fine in a fixture with a good lamp circuit, and if left to warm up and coll down properly, it will look normal again when cool.This is good advice! Many types of lamp look 'ill' when not lit; I've had various brands look rather yellow or grey from the inside and are perfectly ok. Some makes of lamp have chemical deposits inside that are there to absorb impurities in the 'burn-in' period of the first few hours of life. It is these that react to the air if the capsule is ruptured and then they turn permanently white. However I'm not a chemical expert and I'm sure someone else can elaborate on what's going on! Link to comment Share on other sites More sharing options...
Whizzzy Posted November 2, 2009 Author Share Posted November 2, 2009 Thanks for the responses everyone. These are extremely helpful. I've noted the comments about powering up the head without a lamp installed and have taken this on board. There is a dip switch on the fixture marked '0 >5min=off.........Lamp Control' which I had set to 'on'. The manual describes this as "Auto light off after 5 min. of blackout" when set to the off position but I guess that this will still not inhibit the striking of the lamp on first switch on. Could another option be to disconnect the input feed to the ignitor, could this cause any damage to the switched mode supply in the main body of the unit? As an alternative I will check the circuit board for any fuse protection that can be removed. It seems that the general consensus is that the lamp may have turned black due to brief or incomplete ignition so I will check out the wiring from the ignitor with a view to swapping it out from another unit. The main concern however was refitting the lamp in this condition as I obviously don't want it to explode though overheating or should it be the case that when it gets up to temperature the internal composition of the lamp would change and revert back to normal again? At least it is encouraging to know that Osram lamps appear to have a good track record. Link to comment Share on other sites More sharing options...
royzinrotherham Posted November 3, 2009 Share Posted November 3, 2009 Hi another thing to check is that you have a decent mains power supply. poor supply can cause partial ignite and discolouration. Link to comment Share on other sites More sharing options...
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