Hi folks
When checking an old 2108A I found out it sounded like it was filled with sand or gravel
OK, this one has to be re-coned so I put it aside.
Then a year later when trying to repair a 112A cone from old tape and loose paper from the cone I discovered
that one of the drivers terminal was loose. I found out that a screw bit PH-2G was a perfect fit for that screw and tightened it.
Suddenly I remembered the 2108 that sounded so bad and also had a bad DCR reading. When checking the screws on the 2108
I found out that both screws was loose and I tighten them the same way as I had done with the 112A. Then, when the 112A was Ok and was checked on the generator I also checked the 2108 and to my surprise it sounded good, it sounded the same as for the 112A. Wow! both speakers ready for a re-foaming.
Though I have some older JBL speaker in stock I took out every one that was not Ok, some was classified for re-coning others for re-foaming.
I found two LE8T that was bad. Also I found two LE15A that had bad DCR readings (11.6 ohm and the other between 9-15 ohms). Al screws was loose on the Le8 and on the LE15. After tightening al screws the DCR was 5.2 and 5.3 on the LE8Ts and 7.6 and 7.8 for the LE15. After checking them on the generator + a test with music my conclusion was they are alright speakers ready for a re-foaming.
Now whats this al about? Well my first conclusion was that those all speakers had to be re-coned but the fault was the loose terminals: All JBL old speaker/basket terminals are isolated from shorts with plastic (fiber?) )washers, one at each side of the chassis. Speaker connection cables coming from the voice coil is soldered on a ring terminal and the ring terminal are screwed to the basket terminal. After a long time in duty those two plastic washers do crimp probably by ageing or material fatigue (or heat?) and screws come loose. There is also a risk for corrosion on those loose plated screws.
It was a little bit tricky to try to tightening the screws on the LE15 because it was a tight area just behind the cones. I used a screw bit no PH-2G for all screws that I tightened. For the LE15 I had to put the bit in a wrench and secure the bit with heavy tape for to do the job........
The picture shows the plastic washers and where the screws are located. Hope this notes could prevent some of you for to do an unnecessary re-coning