Help me fix these poor ML Sequels

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62sunbeam

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Joined 2011
#1
I picked up a pair of ML Sequels today and unfortunately someone else beat me to the electronics😡

I was told the bass driver worked but the panels were silent when purchased but then they made a little sound after vacuuming.

Before I did anything I opened them and found what's shown in the photos below.

Seems they lost bias and cooked the crossover board, I would imagine from over driving them trying to get more volume out of the failing panels.

I'm going to need a schematic and maybe some handholding and maybe a stiff drink.

Where do I begin?

Any and all help is very much appreciated.

Thanks

Eric





 
#4
Well I'm hoping that comparing the work done with a schematic and checking components to make sure they are to spec I should be able to get these singing again. A schematic would be a huge help.

Can someone tell me how to get the stators off so I can recoating the electrostatic film?

Thanks

Eric
 
#7
The plan is to get the crossovers back up and running using the new caps etc. and replacing anything that's out of spec. Apparently the PO followed DIY upgrade he found on the net. I've seen it, does anyone know of the one I'm talking about and is it a good choice?

How can I be sure once this is done that it is properly functioning if I have a panel that is of suspect condition?

By the way, I hear of people cleaning the electrostatic panel in the shower. How is this done? How do I get it off the speaker?

Can I, using a multimeter, check the electrostatic coating?

Thanks

Eric
 
#8
To remove the panel-mounting rails, you tap the end of the rails with a rubber mallet, and they slide up (or down, depending on the model!), releasing the assembly pins in the rails from their 'wedge clips' in the cabinet.

(Does somebody know the proper term for this type of mounting?)
 

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#9
In case it's not obvious, you must lay the speaker down on its back (on couch cushions) before loosening the rails. Somebody on ML Owners' Forum knocked off their rails while the speaker was still upright, and the weight of the ESL panel broke a solder joint.
 
#10
Well the second crossover is even worse than the first.

There are caps and resistors missing and this PCB is even more badly burned.

I have the hand drawn schematic that floats around the web and it confuses me a little. I know I can figure it out but if anyone has a better one that is laid out more like the actual PCB it would be a big help.

Also, what I have and what the schematic calls out are a little different. First the schematic calls for 400 volt caps, I have 250 volt Daytons in mine and the photo a friend sent me of his ML refreshed Sequel 2 crossovers show 100 volt elpacs.

I assume my Dayton's are OK but want to be sure.

Thanks

Eric
 
#13
The caps could be just fine.
The inductor's are toast and there is a reason for this.

Either they were abused and/or the bias supply quit working and then abused because there was no sound.
And/or, the step-up transformer is shorted due to the abuse causing it to fry the inductors from the overcurrent.

I would start with square one, and that is to determine if the Bias supply is working or build a new one.
Check the step up transformer if it is working properly and get some sound out of the panels first before you waste your money on new crossover components.

The one main reasons is, If you decide to use a different step-up transformer then your new crossover components won't be of the proper values for the transformer should you change it, unless it is an exact OEM part.

Must know the transformers primary inductance before you can start to design a crossover for them.

It is much cheaper and easier to go active as X83 suggested and will cost about the same if not less by the time it is all said and done!!
And, You may very well have a better sound in the long run as well.

FWIW

jer 🙂
 
#14
Actually it appears all the original resistors burned up. Other than one missing inductor they all look original and in good shape.

How do I determine if my bias supply is functional and what resistances should I be looking for in order to determine the transformers are ok?

Thanks

Eric
 
#16
From what I have read about the ML's there should be about 3Kv to 4Kv coming out of it.
You won't be able to measure it with a common DMM unless you make a HV divider circuit as I have described in earlier threads.

Here are the plans as to what I am referring to and hope they give you some idea of how to go about measuring such voltages accurately and safely.

Here are the links,

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/voldiv.html

http://www.diyaudio.com/forums/plan...tor-insulation-mylar-coating.html#post2848194

http://www.esldiy.com/index.php?topic=5.msg24#msg24

http://www.esldiy.com/index.php?topic=177.msg311#msg311

http://www.diyaudio.com/forums/planars-exotics/190716-esl-power-supply-question.html#post3714216

jer 🙂
 

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#18
Yes, most likey.


Second Question~
No, The driving Audio signal and cross over components have very little to no effect on the bias voltage.
I have seen the bias voltage get slightly modulate when the audio signal is stepped up but this has nothing to do with the Bias supply's ability to produce the required voltages under normal circumstances.

If there was ever a chance that the driven audio was high enough to overcome the breakdown voltage of the stack of diodes in the bias supply then I doubt the step-up transformers would even last long enough for that to happen and would most likely burn up First.

jer 🙂
 
#19
Ok. This is what I'm thinking. Since I have most of the components to rebuild the crossovers I'm going to do just that and see what I get.

I am missing one of the larger inductors though so I will need to find a replacement. Can someone tell me the values of the two large inductors so I can check to see which ones I have and find the one I need?

Finally if I don't get sufficient volume after I wash the panels I will recoat them.

Either talk me down or wish me luck.

Eric
 
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