Repair - Electrostatic Loudspeaker

Step 3 – The loudspeaker does not shut down with sparks visible

Connect the speaker to an amplifier with CD player and turn the volume to normal listening level. If the speaker does not shut down with visible sparks.

• Generate an RF spark close to the base of the loudspeaker. This may be created using an electronic cigarette lighter. The loudspeaker should shutdown for 4 to 5 seconds (1 second on very early loudspeakers). Shutdown is recognizable by its quieting effect and while audio may still be heard it will be muffled and distorted.
  
• If speaker does not shut down, check IC1, T1, T2.
• If speaker does shut down, go to step 6B.

Step 4 – Audio output is low

Connect the speaker to an amplifier with CD player and turn the volume to normal listening level. If there is no spark visible with audio output is low.

• Measure the volts across the EHT, it should be between 5 and 5.3 kV.
• If it is, continue to step 6A.
• If it is not, are there between 5 and 5.3 kV at junction of D3, C20, R12.
  
• If yes, check for open-circuit on neon bulb and R12.
• Otherwise, is neon flicker rate much greater than one per second.
• If no, fault lies in EHT circuitry. In cases where EHT volts are slightly low, they can be increased by soldering a similar value resistor in parallel with R13 and R14.
• If yes, continue to 5A.

Step 5 – Speaker makes ticking or fizzing noises

Connect the speaker to an amplifier with CD player and turn the volume to normal listening level. If there is no spark visible with speaker makes ticking or fizzing noises.

• Faulty element due to excessive leakage across the diaphragm. Disconnect the audio leads from the loudspeaker. The loudspeaker should be silent. This test may help to identify the faulty element. Alternatively EHT should be disconnected from each element in turn (remembering to disconnect it from both edges of the diaphragm) working from the top of the loudspeaker downwards and re-checking the leakage by means of the neon flicker rate each time.

Step 6 – Speaker sounds distorted

Connect the speaker to an amplifier with CD player and turn the volume to normal listening level. If there is no spark visible with speaker sounds distorted (Resonances).

• By inspection, if resistors R1a.b.and R2a.b are broken, speaker has been subjected to overload for too long. Replacement of these resistors should cure the fault though in some cases it may also be necessary to replace D11 and D12, TR1.
• By inspection, if resistors R1a.b.and R2a.b are not broken, replace the CD player with a signal generator set at 50 Hz free run sine waves and connect a voltmeter across the speaker terminal. Adjust the volume until the voltmeter reads 8V rms. Gradually sweep up and down the frequency range. The loudspeaker response should be pure and free from rattles at all frequencies except at approximately 50 Hz where diaphragm resonance occurs.
• If there is distortion or low output across frequency range, go to step 2D.
• If audio output low at a particular range of frequencies, there is a faulty element due to open-circuit EHT on one element only. This may be an open-circuit diaphragm. Disconnect audio leads. The element may be isolated by disconnecting EHT from each element in turn (remembering to disconnect it from both edges of the diaphragm) and applying audio each time. The faulty element will be the one which sounds no different whether it is connected to EHT or not.

N.B. It is sometimes possible for elements which have no EHT connected to charge up from adjacent diaphragms. In such cases each element will need to be physically removed to isolate the faulty element.

• If there are resonances at about 40 – 50Hz, the possible causes are :-
• Faulty element.
• Speaker frame resonances due to loose fittings.
• If the resonances is at about 70 Hz, the possible causes are :-
• Loose dustcovers. This is recognizable by a wrinkling effect of the dustcover material and after having removed grilles and cloth.
• Less commonly a faulty bass element.
• If the resonances is at about 90 Hz, the possible causes are :-
• Clips securing the wires to the louvers may be loose. Gentle tapping of these will secure them.
• Less commonly a faulty treble unit.
• Else, other possible causes include :-
• Faulty element.
• Resonances within the loudspeaker due to loose fittings.

Step 7 – No audio output

Connect the speaker to an amplifier with CD player and turn the volume to normal listening level. If there are no spark visible and audio output.

• Audio path open-circuit

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