Mackie SRM450 popwered speaker

[N_Cook]

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 ?

 

[N_Cook]

No, just a decent long screwdriver. I have never sheared a screw in any of
these style of plastic cabinets. Or even come close.




Gareth.

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.

 

[N_Cook]

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 ?

Heated screwdriver worked better than I thought
http://home.graffiti.net/diverse:graffiti.net/heated_screwdriver.jpg
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.
http://home.graffiti.net/diverse:graffiti.net/mackie_horn1.jpg
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.


http://home.graffiti.net/diverse:graffiti.net/mackie_horn2.jpg
http://home.graffiti.net/diverse:graffiti.net/mackie_horn3.jpg
http://home.graffiti.net/diverse:graffiti.net/mackie_horn4.jpg

Cone thing presumably just stuck to the metal,
fell away on removing the

 

[N_Cook]

Don't use a powered screwdriver. As far as the blown HF driver I would
suspect a transient spike or just low quality materials.

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.

 

[N_Cook]

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 ?

 

[Eeyore]

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 ?

Uh ?

I'm sure I've opened one up no trouble. Take the grille off first.

Graham

 

[Eeyore]

Don't use a powered screwdriver. As far as the blown HF driver I would
suspect a transient spike or just low quality materials.

Fit a 24V 21W truck brake lamp in series. It'll protect most low power drivers.

Graham

 

[N_Cook]

Uh ?

I'm sure I've opened one up no trouble. Take the grille off first.

Graham

Take the grill off to change the bass driver but you have to split the whole
case in two to change the horn.

 

[Gareth Magennis]

Take the grill off to change the bass driver but you have to split the
whole
case in two to change the horn.

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.



Gareth.




Gareth.

 

[Eeyore]

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.

Fine, go **** yourself. BTW, I *have* had an SRM 450 apart. Moderadely well made
IMHO but not leading edge electronics.

Graham