Restore dead panels for $100?

[Jazzman53]

This thread is for anyone with panels that lost output and shower cleaning didn't help.
In this situation there's nothing left to lose so keep reading.

I should stipulate that my only experience restoring ML panels was a single Theater Center Channel rebuild, which may or may not be applicable to a full-size panel.

That restoration involved replacing the diaphragm, which had lost its conduction, and was physically damaged by prying the stators apart.

That experience leads me to believe it may be possible to separate the stators without destroying the diaphragm. If so; then merely re-coating the original diaphragm and replacing the charge ring would restore a panel to full volume and extend its life for many years.

My observations from the Theater panel restoration:

• I started the restoration assuming that separating the stators would necessarily destroy the diaphragm so I made no attempt to save it.
• I first attempted to pry the stators apart, which only partially worked, as they were stubbornly bonded, and additional prying risked bending the stators so I decided to cut through the remaining bondlines using a string saw (garotte) made from 60-pound braided fishing line. This worked quite well.
• The diaphragm remained intact where the string saw was used but lifted (disbonded from the rear stator) at the panel end where prying was used.
• The front spars remained bonded to the front stator (very good).
• I observed that by inserting the string saw precisely between the diaphragm and [upper stator] spacer-tape, the string rode atop the diaphragm and cleanly parted the diaphragm from the spacer-tape without destroying the diaphragm or the tape.
• The saw only marred the adhesive coating on the periphery spacer-tape, which remained partially tacky but otherwise intact, so I applied a layer of 4-mil double-sided tape over the spacer-tape to restore it's adhesion, and re-used it.
• After ripping off the original diaphragm from the rear stator, the underlying 20-year old spacer-tape was still pristine-tacky so I re-used it as-is to attach the new diaphragm.

My conclusions from the Theater panel restoration:

• There's a good chance the original diaphragm could have been saved, had I used the string saw from the start (rather than prying).
• The original [stupid-expensive] periphery spacer tapes can be saved/reused.
• On the front stator; the 4-mil clear tape that bonds the spars-to-diaphragm must be replaced (it's cheap).
• On front stator; since 4-mil clear tape will be applied over the marred periphery spacer-tape (to restore its adhesion), it is then necessary to add (1) additional layer of 4-mil clear tape on the spar inner surfaces (to maintain same spacer height).
• The original foil charge ring must be replaced (also cheap).
• If the diaphragms can be saved, the cost to restore a pair of full-size panels would be about $100 ($60 diaphragm coating + $20 4-mil tape + $20 copper foil charge ring).

Basically, the procedure would be as follows:

• Separate the stators using string saw made from 60-pound braid fishing line, starting at one corner and cutting lengthwise thru the bond lines as shown in the attached sketch.
• On front stator; leave spars in place but remove 4-mil tape residue from inner surfaces.
• Remove charge ring from the diaphragm; cleaning off the remnants by solvent wiping with acetone.
• Solvent wipe the entire diaphragm with acetone.
• Mask areas on the diaphragm that will not be coated (see attached sketch).
• Spray-apply one coat of Licron Crystal ESD coating (see video link below). Remove masking tape and air dry for 8 hrs.
• Apply copper foil charge ring (see video link). Charge ring can be applied to either the front or rear stator. If applied to rear stator, place foil adhesive side to diaphragm.
• On front stator; apply one layer of 4-mil clear tape to onto the periphery spacer tape, and two layers of 4-mil clear tape on spar inner surfaces. Leave backing in place until after the sound-check (below).
• Temporarily clamp the stators together, connect power leads, and sound check with music to verify the diaphragm coating is conducting (Licron has never failed me but it's prudent to verify its conduction before permantly bonding the stators together).
• Upon passing sound check, remove backing from adhesive tapes, then mate and press stators together, using hand pressure along edges and over spars.

* There are a couple of reasons why I would not coat the entire diaphragm, within 1/8" of the spars. For the sake of brevity I won't go into that here but if anyone needs to know, ask and I will explain it in a separate post.

Enjoy the music!

References:
ML Theater panel rebuild link: https://jazzman-esl-page.blogspot.com/2011/11/compensating-diplole-phase-cancellation.html
Wire-panel assembly video (different type ESL but some aspects are relevant). Note in this video the charge ring is installed on the opposite stator, whereas ML installs the charge ring directly onto the diaphragm... either method works:

 

[Brad225]

Jazzman, that is great information for all the people that have panel issues.
Whether most of us would have the nerve to try is is another question.
Thanks

 

[Jazzman53]

Jazzman, that is great information for all the people that have panel issues.
Whether most of us would have the nerve to try is is another question.
Thanks

The prospect of having to replace a diaphragm is intimidating, even for a DIY'er-- but if you don't have to replace the diaphragms, a restoration is much simplified.

I was amazed at how well and easily the string saw separated the stators.

I have always used 6-micron diaphragms on my DIY builds, which are delicate, and would likely be shreded by a string saw. Whereas ML uses a much tougher/stonger 12-micron diaphragm, which was not shreded by the string saw.

Think about it:
If you have a dead panel, what is left to lose? It takes very little effort or skill or expense to make a simple string saw and separate the stators.

If, after disassembly, the diaphragms are damaged, you're only out the cost of the fishing line, but if they are intact, the remaining restoration steps are not so difficult.

In fact; I would say that the most difficult remaining step is removing the tape residue from the inner surfaces of the front spars, and I explain how to do that in the Theater panel write-up (it's not hard, just tedious).

It all hinges on saving the original diaphragms-- then all else is relatively easy.