gyro_gearloose Posted April 29, 2014 Share Posted April 29, 2014 Hi Has anyone got the wiring diagram or service manual (if there is one) for Martin 918s? One of mine has an odd problem where the pan and tilt sometimes lose position. I think this is being caused by a lack of torque to the motors, which in turn would be caused by a loss of volts. I've swapped driver chips and motherboards around and the problem stays with one unit, suggesting that the problem is either with the motors or the transformer and not the driver chips or that old Martin favourite, cooked current sensing resistors. I'm fairly certain that the pan and tilt motors have a different power supply to all the rest, running at a higher voltage, but I'd need a circuit diagram to confirm this. I do have a couple of units I can cannibalise for spares, so swapping parts round won't be too much of a problem. Link to comment Share on other sites More sharing options...
aziz Posted April 29, 2014 Share Posted April 29, 2014 One thing to check is that there is a plastic clip with a spring on the end of it on the shaft of the motors.From what I can remember they lock the mirror in place to stop it dropping out of position. Link to comment Share on other sites More sharing options...
marktownend Posted April 29, 2014 Share Posted April 29, 2014 It's a long time since I've worked on a 918 but I've got a vague recollection that if everything's not set completely in the right place that there can be a physical clash between the mirror and the large curved panel behind it. Unfortunately I can't remember if it's to do with the panel positioning or the position of the tilt motor on the shaft of the pan motor or what, but it might be worth you checking. I may well be talking rubbish but there's a bell ringing somewhere rather too deep in my grey matter... Link to comment Share on other sites More sharing options...
KevinE Posted April 29, 2014 Share Posted April 29, 2014 Pan & tilt share the same 30V rail as the other motors. If you're 100% sure the fault stays with the fixture when you swap boards, my bet will be the motors worn out. Check the tilt harness is ok behind the mirror and that you haven't accidentally swapped the pan & tilt plugs at the board end. Check the plugs have no corrosion inside them, meter them from motor to underside of pcb pins for high resistance. Check as already mentioned by marktownend that the mirrors are correctly positioned on the motor shafts so that in test mode the mirrors will consistently go left/centre/right without touching the hard stops. You can check the motor torque by comparing the 'feel' with your good light. It's common for the magnetism to go weak resulting in perfect operation on slow movements but skipped steps when the mirrors are moved fast. Some main board firmware revisions have a 'tilt motor type' parameter to accomodate old or new style motors which have different drive characteristics, check this if you want. Link to comment Share on other sites More sharing options...
MrBoomal Posted April 29, 2014 Share Posted April 29, 2014 Probably not helpful, but, new replacement 918 mirrors do not fit older 918's, and as Mark said will clash with the back panel. This can knock your pan & tilt all over the place. Link to comment Share on other sites More sharing options...
gyro_gearloose Posted April 30, 2014 Author Share Posted April 30, 2014 Pan & tilt share the same 30V rail as the other motors. Sure about that? I've got a motherboard here in front of me and I can see six wires coming in from the transformer going to three rectifiers. One is tiny and presumably feeds the CPU. The other two are quite large, are attached to a heatsink, and are surrounded by several large electrolytic capacitors. This would suggest that there are two power supplies for the motors, one for pan and tilt, and one for everything else. I've seen this kind of setup on other moving lights, so I am assuming that Martin have followed suit. If you're 100% sure the fault stays with the fixture when you swap boards, my bet will be the motors worn out. Check the tilt harness is ok behind the mirror and that you haven't accidentally swapped the pan & tilt plugs at the board end. Check the plugs have no corrosion inside them, meter them from motor to underside of pcb pins for high resistance. Check as already mentioned by marktownend that the mirrors are correctly positioned on the motor shafts so that in test mode the mirrors will consistently go left/centre/right without touching the hard stops. You can check the motor torque by comparing the 'feel' with your good light. It's common for the magnetism to go weak resulting in perfect operation on slow movements but skipped steps when the mirrors are moved fast. All good advice. The fault does stay with the unit so its most likely going to be a motor fault. When I get the units back in my workshop I'll check the motors over and see which ones are worn out. Link to comment Share on other sites More sharing options...
timsabre Posted April 30, 2014 Share Posted April 30, 2014 Check for ripple on the PSU as well, sometimes the smoothing caps dry out and the power rail becomes very ripply, this can reduce the motor torque. Link to comment Share on other sites More sharing options...
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