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 small Theater Center Channel rebuild, which may or may not be applicable to larger panels.

Absent complete knowledge, it will be assumed that all ML models are constructed like the Theater panel, with its stators bonded together at the periphery and across all spars.

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

Lessons learned during that rebuild leads me to believe it might be possible to separate the stators without destroying the diaphragm. If that were possible; then merely re-coating the intact original diaphragm (easy to do), and replacing the charge ring (also easy), would restore a panel to full volume and extend its life for many years.

My observations from the Theater panel restoration:

• I had assumed that separating the stators would 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. Further prying risked bending the stators so I opted instead 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 in areas 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), so I left them in-place.
• 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 periphery spacer-tape without destroying the diaphragm or the tape.
• The saw destroyed the 4-mil clear tape used in the front spar-to-diaphragm bondlines but only marred the adhesive coating on the 25-mil periphery spacer-tape on the front stator, which remained otherwise intact, so I left that tape in-place and applied a layer of 4-mil double-sided tape over it (to restore it's adhesion), and re-used it.
• After ripping off the original diaphragm from the rear stator, the underlying 20-year old 45-mil 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, to separate the stators, rather than attempting to pry them apart.
• 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 would be added 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 a periphery charge ring using conductive-adhesive-backed copper foil tape (see video link). The charge ring can be applied to either the front or rear stator-- if applied to rear stator, place the foil's conductive adhesive side to the diaphragm.
• On the front stator; apply one layer of 4-mil clear tape to over the (marred) periphery spacer tape, and two layers of 4-mil clear tape on spar inner surfaces. Leave all tape backing in place until after the sound-check (see below).
• Sound-check: 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 permanently bonding the stators together).
• Upon passing the 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.

So the question remains;
Is it possible to restore dead panels without replacing the diaphragms?

Inquiring minds want to know!

Hopefully, someone with a dead panel will give the string saw a go and answer to this question.

Enjoy the music

References:
ML Theater panel rebuild link: https://jazzman-esl-page.blogspot.com/2011/11/compensating-diplole-phase-cancellation.html

The video below depicts a flat-panel, wire stator ESL, but the bias wire to charge ring connection, and coating the diaphragm would be applicable for ML panels. 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 separating the stators, the diaphragms are damaged and you opt to take it no further, you're only out the cost of the fishing line-- but if the diaphragms 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.

 

[JonFo]

Charlie, thanks so much for this write-up; it's quite clear what steps to take.
From my experience operating SL3 and Monolith panels, this fishline string saw trick would have saved me much effort, even though my goal was simply to have bare stators.

I will try this on the next set of panels I split apart (my rear Sequels, most likely).

 

[Jazzman53]

Charlie, thanks so much for this write-up; it's quite clear what steps to take.
From my experience operating SL3 and Monolith panels, this fishline string saw trick would have saved me much effort, even though my goal was simply to have bare stators.

I will try this on the next set of panels I split apart (my rear Sequels, most likely).

Thanks Jonathan,

I'm really curious to see if the string saw will work on larger panels without shredding the diaphragm.

The Theater panel was small, having a short side-length tape line and only two spar bondlines to cut thru, which did not impose a huge drag on the string.

I think the bigger issue with a larger panel would be getting thru the much longer edge bondline on the panel side.

I think you would need to start with the string saw oriented at a 45 degree angle to get thru a corner, but then you would need to transition the angle to vertical (or only a very slight angle), to avoid cutting across the panel in the curved direction.

So I think getting thru the side periphery tape would be the most difficult part, as the string would be imbedded thru practically the full-length of the side bonline, which would impost a lot of drag.

It should be easier to start at an upper corner and cut thru about half of the side bondline, and then move to the lower corner and cut thru the remaining side-bondline.

No doubt, the additional panel length and additional spars would add to the difficulty but I'm optimistic.

Charlie