Blown horn - anything to check on , in the way of ultrasonic oscillation as went during normal use? How to break the cab in 2 ? Deep recessed screws tightly bound in dense plastic. I know , from similar situations, it is quite likely to shear the screws with the undoing torque required. Soldering iron heater slid over the end of the long shaft screwdriver to locally melt the plastic ? Dropped power to it for enough heat but relatively low temp to penetrate the length of the screw ?
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I've broken one years ago , with same sort of stiction? / excessive torque ,in a power drill, long screw into hard plastic. These Mackie screws, 17 of them, (2 slightly shorter either side of the bass driver) , in my opinion , are bordering on the threshold of shearing without such heating, they deliberately used undersized holes probably.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Pic shows the original soldering iron heater, for unknown model. The one used with flange ground off , added silicone sleeved wire and PTFE covering the heater, slid over the end of the driver shaft. And one of the long screws, mm /10mm/ 20mm graph paper. Used about 10 watts, could have gone higher as no plastic melted onto the PTFE. Drilled out the screw holes a bit for easier assembly/ next disassembly , (will add star washers under heads) Caproic smell came off - what do Americans use as glue or filler for construction plastic ? I only smell it with USA equipment.
While heating one 10 inch recessed screwhead, extracted the previous heated one. Further general tip - slide some grommets onto the second extracting driver to locate easily on the head, for deeply recessed screws.
So the second of 2 Mackie SRM450 to have mechanically broken tail at the voice coil. Previous , different unit, bass driver coil broken where the coil wire is deformed to flat for the tail. Not the slightest trace of overheating on that one. This one, horn , nearly at this tail juncture , the break marked B below, half turn vroken away from the resin core, and again so trace of overheating anywhere.
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4 engineering bolts hold the diaphragm to the magnet but it is set in plastic frame, although engineering plastic, presumably can deform enough to catch something.
As there is a milled out recess R already there I intend trying to take the + and - tails through the same side, not diametric. Grinding a slot in the aluminium ring to take some 3x3 plaited 46 swg wire as tail. Replacement driver 130 USD , diaphragm 70 USD so worth trying as presumably swap USD for GBP and add some for here. Very little diaphragm movement so should not foul anything.
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Cone thing presumably just stuck to the metal, fell away on removing the
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
It would seem to be a generic Mackie voice coil failure. Their low quality technique seems to be a specific length of 0.07mm wire, in this case, flattened to something like 0.02 x .2mm at either end. This of course increases the resistance and acts as a fuse. When I touched that broken free curve of wire, in the pic, it disintegrated. Only that had been heat affected, nowhere else. Start winding with the flat at the " inlet" position and then 25 turns later have to wind the ribbon part around the former as a final part turn to reach the appropriate feed out point. It was the same with a bass driver I previously saw. Little point in replacing with same, spending silly money. If they want fuses in line then there are far more sensible approaches.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
The wire used is actually silver, so resistivity 1.6 × 10-8 Ohm-m compared to copper of 1.7 × 10-8 Ohm-m. Only marginal difference , probably destroyed by the tails flattening, so why silver ?
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Tch. That's Graham again pretending to be knowledgeable but really having no clue at all.
You don't need to remove the grille, as you have ascertained, Mr Cook, having worked on a real example - not some distant memory of something that may or may not have been a Mackie SRM450, Mr Stevenson.
Graham, please keep your mouth shut unless you can add something useful. BTW I won't and don't want to see your replies, you are killfiled for posting useless garbage like this amongst many other offences.
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