Repair - Electrostatic Loudspeaker

This is a simple guide on diagnosing the ESL-63 loudspeaker. In order to successfully diagnose the ESL-63, all the listed steps have to go through sequentially. Skip only if the problem does not occur in those steps.

Cautious :- Extreme care should be exercised when carrying out the following test as contact with the secondary side of the audio transformer under signal conditions can be fatal.

Step 1 – The loudspeaker has no power

Apply AC supply volts and if the “POWER” LED does not turn on.
These are the possible causes.

• Open-circuit AC supply fuse.
• Voltage selector in between 110V and 240V.
• Intermittent AC supply switch.

Step 2 – The loudspeaker always shut down

Connect the speaker to an amplifier with CD player and turn the volume to normal listening level. If the speaker shuts down with

• Sparks visible in the speaker base in a darkroom.
  These are the possible causes.

• Dry joint.
• Broken connection.
• Faulty audio transformer.
  
• Spark visible in the speaker on a soldered joint with the speaker cloth pulled down and grilles removed.
  These are the possible causes.

• Clips or wire links dry joint.
  
• Spark visible in the speaker between two of the copper rings of an element with the speaker cloth pulled down and grilles removed.
  These are the possible causes.

• Faulty delay line coil. The fault may be narrowed down to one of two coils, these being the coils which feed the two copper rings between which the spark is occurring.
• Faulty element.
  
• Disconnected antenna or the output is low or distorted. Replace the CD player with a signal generator set at 50 Hz pulsed sine waves and connect an oscilloscope to the primary of L15 with the sensitivity set at 10V/cm. Check that the clamp circuit is functioning correctly by increasing the volume on the amplifier while observing the transient trace on the oscilloscope. An approximately 28V to 29V clipping should occur indicating that the signal is clamped.
  
• If the clamp circuit is functioning and the speaker is sparking.
• Faulty element.
• If the clamp circuit is functioning and the speaker is not sparking.
• Discontinuous EHT, suspect broken link.
• If the clamp circuit is not functioning; disconnect audio, check DC volts on gate of T1.
• If it is greater than 0.25V.
• Faulty IC1 holding T1 “on”
• If it is lower than 0.25V.
• Vr1, T2. (where fitted)
• R1 a.b., R2 a.b. – O/C, D11, D12.
• If the AC supply volts are low, particularly on early loudspeakers suspect T3.
• Spark not visible in the speaker with the antenna disconnected, the speaker cloth pulled down and grilles removed.
  Faults of this nature usually prove difficult to locate. The antenna being disconnected may cause the fault to progressively worsen resulting in the spark becoming visible. This test may also encourage the spark to become visible. The most possible faults are:-

• Dry joints on audio or EHT clips.
• The base, the speaker elements or more commonly the coil board assembly.

The loudspeaker should be inverted with audio and AC supply leads disconnected. With the base plate removed, reconnect the antenna and disconnect the red and white wires which run from the audio transformers to the coil boards, at the coil board end. In the following tests loudspeaker shutdown may be identical by a flattening of the oscilloscope trace or illumination of an LED connected between T1 gate and earth. Connect AC supply and audio leads. Replace the CD player with a signal generator set at 50 Hz pulsed sine waves and connect an oscilloscope to the speaker terminal with the sensitivity set at 10V/cm. Increase the volume to a bearable level and sweep up and down the frequency range listening for loudspeaker shutdown, indicating the presence of a spark. Sparking is generally as a result of insulation breakdown which is most likely under these extreme conditions. At frequencies above 12 kHz where shutdown may be difficult to identify the oscilloscope should be observed. The transient waveform trace will decrease in amplitude if shutdown occurs.

If sparking is indicated the fault lies in the loudspeaker base.

If sparking is not indicated disconnect the audio and AC supply. Remove the loudspeaker base. Disconnect all of the black wires from the coil board, then refit the speaker base with the EHT and the red and white audio transformer wires re-soldered.

Apply AC supply and audio. If sparking is indicated the fault lies in the coil board. If no sparking is indicated the fault lies in the speaker elements or wiring.

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