Originally Posted by
RMC
Hi VintageUT,
RE "I stole that idea from someone else." Then I may steal it from you for future use, fair game: robber robbed, lol.
Lol, well played.
Removing the dustcap isn't rocket science. If you have a stable non-shaky hand and can do detail work you pretty much have what it takes.
I am sure I have what it takes to successfully remove the caps and clean the VC gap.
From the driver pics seen on the Web, 128H white cone has a screen on driver back vent and 128H-1 black cone has a bare hole on the back presumably with some foam in it. Yours may also be a "hybrid" 128H-1 with 128H white cone?? Mine are the 128H white cones with back vent.
First check the driver's back vent to see if you have a screen there. JBL mentioned drivers have a screen or a foam plug to cover the back vent hole. If its a screen still try to look through it with a good flashlight to confirm the absence of some foam. If no foam, that reduces the possibility of rotten foam having migrated in the gap. If your model has no screen then it probably has foam in the back vent hole and that foam could have desintegrated and migrated in the gap. Btw a screen with no foam seen doesn't guarantee there's nothing in the gap, it may be something else, or other issue.
I used a bright flashlight and can see there is a foam vent still attached. It looks to be in place, but with the age of the foam, it would make sense there could possibly be bits of foam in the VC gap. It’s just strange the other driver works well when this one doesn’t.
Cut the dustcap in a way to save it (see below), clean the Gap and to use shims for the refoam. You need to be careful doing this, just take your time.
You don't have to cut dustcap all around like for taking it off completely. You can cut ALMOST around it but STOP cutting just a bit before the wires covered with black glue. That means there's about 3/4" of UNCUT dustcap left still holding it in place, this way you can reuse the original dustcap.
This makes sense! Love the idea of using the original cap.
You need cutting cap HORIZONTALLY and straight, ALWAYS just above the black glue line to avoid damaging the round voice coil under cap. Cut delicately with a very sharp blade using a back and forth movement, after initially piercing the cap (I use scalpels, but a sharp exacto should do).
When that is done, lift up the dustcap SLOWLY and make it hold upwards at a right angle (no more) with a piece of not too sticky tape from cap edge to driver frame. I typically use 3M Blue painter's tape for that purpose since its made for easy removal. Some lower cost beige color masking tapes are often too sticky to be removed easily, so prudence re damaging cap. At this point you should see inside the driver: the vent hole, voice coil and gap.
This is the worst part, other than refoaming. Knowing what the job entails, we'll see if you plan to do it yourself or let someone else do it for you. If need be we can discuss further steps based on your decision. Regards,
Richard