Dette er skrevet av en prof. (Ikke meg)
#1. You gotta clean the gap...and the slits in the phase plug....and the driver throat. Bits of dirt, metal chips, voice coil former residue...anything....MUST be cleaned out of the gap. Use 1" masking tape adhesive-side out folded outside of some card stock to dig into the gap. When the tape comes out clean after several times around the gap, then clean the gap again with some coffee filter paper dipped in acetone to clean out any tape adhesive bits left behind. Inspect the gap with a lighted magnifier to make sure it's CLEAN...there's only a few thousandths of an inch tolerance on either side of the voice coil when it's immersed in the gap, so this step is critical!...or you'll risk early mortality of the voice coil.
#2. Check the gap width uniformity with a gap guage (.031" on most 1" throat drivers) to make sure the top plate or phase plug hasn't shifted slightly. Alnico drivers can shift a little. The newer ceramic drivers are glued together...so any misaligned gaps are probably factory defects, which is rare...or it was dropped and broke loose. If you get adventurous and take apart an Alnico driver, the magnet will discharge, and subsequently need recharging.
#3. Clean the gap....again. Possibly metal chips from checking the gap tolerance found their way in.
#4. Inspect the new diaphragm. Check for high voice coil windings, check for roundness...sometimes they're not, right out of the box, and the consumer has not much recourse, because when the part leaves my shop in the box, I have no idea what went on from there...read the enclosed disclaimer...and the guy who put it in, NEVER does anything incorrectly...his dog ate it
#5. Trial fit the new diaphragm. Locating-pin holes are not always the same size as the locating pins. The diaphragm should fit snug on the pins but shouldn't need to be forced into place. If that's the case, the locating-pin holes need to be reamed out a bit....newer ceramic units have a relief machined into the top plate that the diaphragm drops into.
#6. Install the three diaphragm mounting screws...loosely....don't tighten down yet...just enough to hold down the mounting ring. Apply 3.5 volts(for 16 ohm, 2.83 for 8 ohm) test sweep tone from 500-1200Hz, and listen for any buzzing. Sometimes the diaphragm must be adjusted slightly to eliminate all buzzes. It's a good measure of thoroughness to sweep beyond the test frequency to ensure clean travel to lower frequencies, and adjust out any higher frequency anomalies. After all, these are always getting more program than the test frequencies...it's good to be thorough. Snug down the screws when it sounds clean and buzz and resonance free, while sweeping with test tone. BTW...polarity on the sweep test does not matter.
#7. Check the condition of the foam pad inside the loading cap. Get a replacement if its rotten. Check the condition of the lead wires. Make sure there are no short circuits to the loading cap from the outside spring terminals to the inner lead wires. Connect the lead wires to the properly colored terminals. Make sure the wires are lined up with the correct terminal. You don't want to twist and criss cross the wires when reinstalling the loading cap....cap needs to fit airtight. RED is NEGATIVE, BLACK is POSITIVE...yes that's right, it's backwards from what you're used to. Polarity conventions have been changing in the last few years to standardize with other mfr's products.
#8. Re-install the loading cap. Make sure it seats fully down to the top plate with no airleaks and the lead wires aren't resting on the diapragm dome...that doesn't sound good.
#9. Do a final thorough sweep test to the fully reassembled driver to makes sure it's good to go.
#10. It's cheap insurance to have the JBL Authorized servicer do the replacement. If the diaphragm fails due to user installation error....you're pretty much on your own.
