Tuesday, 4 October 2011

Quad Electrostatic Loudspeakers - Replacing Noisy Panels

If you've owned Quad electrostatics for any length of time, you're probably familiar with the odd noises that can occur when there's a problem - fizzing, screeching, whistling and rustling.  All normally caused by a leakage of the EHT voltage somewhere within the speaker.   The usual is a breakdown of insulation on one or more of the panels.  You'll need to try and isolate where the problem is before ordering parts or making a repair.

To ascertain where the problem is, you can usually roughly locate it by running an ear closely over the entire speaker frontal area.  Once you think you know where that area is, you will often be able to see a discharge or sparking at the exact spot.  This is best done in a darkened room (it can be very faint), and you may need to roll down the "sock" (grill cloth - read on for details).

This is the procedure that I've adopted to repair or replace panels in the Quad electrostatic speakers.  This is written for the 988 / 989's, 63's are very similar and it could easily be adapted for them.

Please don't ask me to do this for you, it takes a lot of time and requires a lot of space, two things that I don't seem to have much of lately!

988's (and 63's) have four panels arranged in a vertical stack, 989's have two additional panels, one each at top and bottom.  In both cases, the centre two have a "bull's eye" pattern which is the arrangement of delay driven concentric rings which generate the point source imagery.

If you want a bit of history, or to get really technical about how ESLs work, here's a few interesting links:-


Quad will undertake this work at very reasonable cost, so unless you really want to have a go yourself, it's worth checking with them first. However, shipping is expensive and you'll need the original packing cases.  You can arrange to drop off your faulty speakers in person. I believe they no longer offer support for the ESL57s.

One Thing Audio will repair your 57s or 63s.  They will even refurbish your original panels or offer a service exchange.

ESL 989, Black

If you are to attempt this procedure, take some time to familiarise yourself with this information before starting and get all the parts in first.

  1. As well as the replacement panel(s), make sure you have replacement dust cover kits (available from Quad’s service department) to hand before commencing – you will need them!  One for each side of the loudspeaker, I've found that there's enough to allow for a mistake.  You will also need some black cloth tape – duct tape or gaffer tape is ideal.
  1. Be sure that the speaker has had adequate time disconnected from the mains to allow discharge of the high voltages within the assembly.
  1. Remove the top plate – a sharp tap with the heel of your hand (left side, looking from the front) will unclip it from the top moulding.
  1. Release the “sock” from the grip on top of the speaker and pull it down away from the top of the speaker (it will later be removed altogether).
  1. Remove the black cloth tape from around the end of the panel which is holding the grill and moulding together and preventing rattles.
  1. Remove the top moulding by removing the 4 self tapping screws (15mm) to the top corners and releasing 3 self tapping screws (9mm) per side at the top of the grills.  The top moulding will also be attached with double sided tape against the grill – break this as necessary by gently prying with a screwdriver, the top moulding will now come away.
  1. Turn the speaker up-side-down (rest it against your work bench or a table) and remove the base plate (held by 17 self-tapping screws (9mm) with toothed washers.  Watch out for the ground wire inside the base and disconnect it as the plate is removed.
  1. Disconnect (by de-soldering) the two red HT wires from the vertical PCBs attached to the lower moulding.
  1. Disconnect (by de-soldering) the yellow signal wire from the drive PCB attached to the base of the speaker (along with the transformers).
  1. Withdraw and release the red drain wire which is held in position by the vertical PCBs and stops short of the side of the base moulding.
  1. Remove the base moulding complete with its electronics by releasing the 8 silver M4 hex nuts and flat washers.  Note the black grounding wires attached by these.
  1. Now the sock can be completely removed out of the way.  Keep the speaker assembly up-side-down.
ESL988, Vintage

  1. Remove the black cloth tape from around the end of the panel which is holding the grill and moulding together and preventing rattles.
  1. Remove the front and rear grills of the speaker by releasing 3 self tapping screws (9mm) per side then gently pry the bottom of each grill (presently at the top!) away from the base moulding, breaking the double sided tape.  Continue in such a manner that the grill can be slipped out of the side mouldings and away from the frame.
  1. Clean off the old double sided tape from the mouldings and the grills.
  1. Very carefully cut away the film dust covers from both sides of the ESL (cut as close as possible to the double sided tape which is holding them in place).  If you find the old tape is stuck very firm and will not come away easily, leave it in place, otherwise it may be removed.
  1. De-solder the wiring to the top and bottom edges of the panel to be removed (both sides).
  1. If the grey wires from the delay circuitry are in the way of the panel you wish to remove, carefully break the glue bond holding them to the panel lattice and dress them away from the panel.
  1. Remove the 4 self tapping screws (25mm) to the sides of the panel to be removed - these are holding it to the speaker’s frame.
  1. The panel can now be removed from the speaker.
  1. You will notice a central wire from top to bottom on the rear of the faulty panel - remove this and the clips holding it to the plastic lattice, fit it in place on the new panel.
  1. Fit the replacement panel in reverse order, screw in place and then re-attach the wiring.
  1. Reposition any grey wires that were dressed out of the way earlier and put a small spot of adhesive at each slot in the panels such that they will not vibrate and cause unwanted noise when the ESL is operating.
  1. Refit the top moulding with the 4 self tapping screws (15mm) to the corners.
  1. Stick new double sided tape (from the dust cover repair kits) around the edge of the loudspeaker frame, front and back, over the old tape.
  1. The dust cover film can now be stuck in place (do one side of the speaker at a time and refit the mesh grill afterwards to avoid damage during further handling).  Try rehearsing this procedure in your mind before attempting it
This procedure is best done by two people.  Place the ESL face-down on a flat surface and remove the backing from all four strips of double sided tape.

Carefully stretch out the film above the ESL, pulling it as flat as possible (be careful not to pull too hard as to tear the film).  Lower it down on to the tape whilst keeping it as wrinkle free as possible.  This is best achieved by sticking down either the top or bottom end first, whilst holding the film just above the speaker (3cm or so).  Do not let the film droop and stick to the tape.  Move down the sides, keeping the film taught and sticking down about 30cm at a time.  Finally stick down the opposite end to where you started from.  There will be some wrinkling which can be removed afterwards as described below.

Make sure the film is stuck down all the way around the speaker frame and trim to size close to the tape outer edge.

The wrinkles in the dust cover must be removed, since these will produce audible rattles.  This is achieved by means of heat which thermosets the plastic film and may be applied by a warm air blower, such as a domestic hair dryer.  You will find this easier with the speaker standing on end.

The nozzle should be held close to the dust cover and moved from side to side across the unit slowly and steadily in regular lines to cover the whole area.

To achieve sufficient heat to thermoset the plastic, it may be necessary to restrict the supply of air to the dryer by placing a hand over the intake.  This can be dangerous so ensure that is equipped with a thermal cut-off.

Repeat the process until all wrinkles have disappeared, but always treat the whole area and do not tackle individual wrinkles separately.

A certain amount of skill is required in the operation. Obviously, if the nozzle is not close enough and/or the speed of travel too great, there will not be enough heat to affect the cover.  On the other hand, too much heat at one point can quickly burn a hole.  When carrying out this process for the firs time, progressively reduce the distance and speed until the desired results are obtained.

An “industrial” hot air gun, such as those used for heat-shrink tubing, is a lot more powerful so proceed with caution if you intend to use one of these – you will need to move it faster to avoid holes appearing in the film!

Take your time with this process and persevere if you damage the film.  It will be frustrating to start over, but, as mentioned, there is usually sufficient tape and film in the repair kits to allow for a disaster or two!

  1. Don’t forget to re-fit the grill to the side you have completed, this will protect the work you have achieved so far.  Some new double sided tape is required along the top and bottom edges of the end mouldings to prevent the grill rattling.  Once the tape is in place, remove the backing in preparation for the grill.  Slot the grill into the rebate one of the side mouldings.  Bow the grill across the front of the speaker and slot it into the other side moulding.  Be careful not to slip and damage the film you have just finished.
  1. Repeat the procedure for the other side of the ESL.
988 and 989, Nouveau

  1. With the speaker standing on end (bottom upward), put some new black cloth tape (approximately 2cm wide) around the bottom end of the speaker in order to bond the grill and moulding together and prevent rattles.
  1. You can now replace the sock over the speaker.  The seam in the material should be positioned to a rear corner and thus be less visible.  Carefully feed the sock over the end of the speaker, being sure not to ladder the material on the way.  Pull it down the speaker as you go in order to get the bottom (presently facing upwards) tidy.  Leave about 3cm surplus material for fixing in place.  When you are happy with the positioning of the sock, press the surplus material at the end into the grips on the end moulding.
  1. Next re-position the base moulding and electronics over the 8 M4 studs at the bottom of the panel.
  1. Place the 8 silver M4 clear flat washers over the 8 studs.
  1. Replace the black grounding wires onto the M5 studs - 2 to each side.             
  1. Tighten down with the 8 silver M4 hex nuts.
  1. Reposition the red drain wire through the holes in the vertical PCBs and pull through towards the side of the base moulding stopping short of the side at approximately 3mm.
  1. Re-connect (by soldering) the yellow signal wire to the drive PCB attached to the base of the speaker (along with the transformers).
  1. Re-connect (by soldering) the two red HT wires to the vertical PCBs attached to the lower moulding.
  1. At this point, apply mains power to the loudspeaker and switch on, allow a few minutes for the elements to become properly charged.  BE AWARE OF HIGH VOLTAGES AT THE ELECTRONICS WITHIN THE BASE – DO NOT TOUCH THE INTERNALS WHILST MAINS POWER IS APPLIED, ALLOW SUFFICIENT TIME FOR THE EHT TO DISCHARGE BEFORE HANDLING.
  1. Check over the loudspeaker for spurious noises indicating other panel defects.
  1. Note the neon lamp (N1) on the control PCB - this should be flashing at around 10/second.
  1. Refit the base plate (held by 17 self-tapping screws (9mm) with toothed washers.  Don’t forget to re-connect the black ground wire inside the plate.
  1. Turn the speaker over and stand it upright on its base.
  1. Put some new black cloth tape (approximately 2cm wide) around the top end of the speaker in order to bond the grill and moulding together and prevent rattles.
  1. Pull the “sock” up the speaker, stretching out any wrinkles, and press the surplus end into the grip on top of the speaker.
  1. Refit the top plate – align the two pegs into the brackets in the top moulding, a sharp tap with the heel of your hand (right side, looking from the front) will clip it into place.
  1. Reassembly is now complete.
  1. Apply mains power and connect to an amplifier output.  Switch on and allow the elements a few minutes to charge up.  Play some music and check for correct operation, enjoy!

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