【 Weak current College 】 common electro-acoustic devices of amateur test---Power By 【 China power house network 】

1 loudspeaker
1. check the structure from appearance
The speakers from outside observation is rusty iron frame; cone is damp, musty, rupture; the leader have wuduan wire, solder or weld; magnets are wrestling down crack, shift; use gaizhui near magnet check its magnetic intensity, etc.
2. is the negative terminal of the judgment,
The multimeter in 0.5mA, two table Rod respectively in test speaker two lugs, fingers touch the speaker cone to Cone connection of coils in the magnetic field lines movement in incising, then there will be induced current generation, accessible from the multimeter observed on the direction of deflection. If the pointer deflection clockwise, the black table at the end of the rod received as cathode, contrary to the cathode.

3. coil and impedance testing
The multimeter in R× 1 retaining, using two table bar (without anode and cathode) dianchu its terminals, hear the obvious "giggles" sound, that coil not circuit breaker. Then look at the table where the needle stays, if measured by the impedance of the marked resistance similar to illustrate the speakers sound; if the actual resistance than nominal resistance is much smaller, speaker coil turn to turn short-circuit exists; if the resistance of the coil for ∞, description, internal circuit breaker or terminals possible breakage, welded or soldered.
4. sound distortion measurement
(1) cone broken cone is an important part, the sound should be focused on checking whether the broken cone. When a speaker cone rupture, playback will produce a "Squeaky" sound; if the cone damage seriously, worms decay bite, the damaged area is large and cannot be repair can be abandoned.
(2) voice coil and magnet touch, voice coil magnetic in magnetic steel in movement, the more chance of damage. Finger touch paper cone basin, if difficult to up and down movements, coil is magnetic steel stall. For two reasons: one is the speaker broke down, cores, offset; another is the cone and the coil attached to offset or deformation, causing the voice coil in vibration and magnetic steel produce mutual friction so that voice to ask questions or send out sound, light, the sound produced "sand" sound and distortion, to make the voice coil loose or disconnected.
Second, piezoelectric ceramics-speakers
1. Visual inspection
Piezoelectric ceramic-speakers, called Crystal-speaker, check the piezoelectric film surface is not damaged, cracked; leader is unsoldering, soldered.
2. detection of the "piezoelectric effect"
It is not easy to detect with multimeter DC impedance, but can subtly use "piezoelectric effect" inverse process to detect. The multimeter in µA, two table bar, regardless of the positive and negative electrode attached to two poles of piezoelectric chip pinout, and then use the Pencil Eraser head light pressure placed on the desk or glass plate piezoelectric films, look at the table head pointer is swinging. If there is an obvious swing meter, piezoelectric films intact, piezoelectric patch failure.
3. moving coil microphone
1. from the appearance of the structural testing
Should take the first outside the method after testing, such as distortion occurs, first check the audio headers are damp, whether between voice coil and magnetic steel brushing; then multimeter check voice coil impedance and nominal values are similar. As silent, first check the voice coil wire is loose, bad; and then use the multimeter check-off. You should also check the switch with no loose; plugs without unsoldering; cord of cores and shielded cables have no circuit breakers, etc., through the skin and electrical testing, you can find fault resides.
2. silent failure of judgment
General microphone (such as household karaoke microphone), its DC resistance are 600 ± 10 Ω. Multimeter R× 100, test plug hub side and shell, open microphone switch placed ON the resistance should be 600 Ω. If untestable impedance, description of the microphone from plug → switch → tone head office there are circuit breakers, available multimeter — a detection. First swing open the front cover, direct measurements audio header pinouts on both ends if R = ∞, prove that internal open voice coil; if R = 600 Ω, proving that good, failure in the voice coil plugs or cord and switch, practice has shown that several frequent opening of the phenomenon: such as cord of shielded cable to easily broken, its core wire solder; switch internal bad or wire solder, etc.
3. tone detection of light and distortion
First swing tone head front cover, observation of vibration film has been flat, has no flexibility. Multimeter R× 1 block, two table Rod Dianchu tone head ends, the sound is very small, instead use R× 100, measured impedance, if impedance 300 Ω or so there, voice coil turn to turn short-circuit, causing the decline of electromagnetic induction. If Dianchu tone first two terminals have obvious "sand" sound, that voice coil and magnet touch, sound, produced by friction represents the voice coil or vibrating membrane location change, cannot be used. If you discover any other malfunctions, is declining, Alnico magnetic only replace the tone head.
4. in the event of a serious screech of discriminant
Whistler is a common fault of microphones, based on practical experience with the following reason: ① cord in shielding the cable was broken or next to the plug Shield line falls off, only its core wire properly. When the microphone plug to plug in the amplifier for Jack, shielded cable, which is equivalent to the Earth wire is broken, handheld microphone of the human body sensors or outside interference will be transmitted to the amplifiers in self-excited oscillation and whistling. ② replacement tone head, because the cord in the core and the shielding line by toggle switch then leads to two wire welding head of sound, very easy to create Center lines and docking power amplifier for land-side, and the shield line amplifier input. For plastic tube shell of the microphone discover problems, nor does it produce a whistling, but for metal-tube shell of the microphone, because the handheld metal shell add-in is in the human body sensors on the introduction to the power amplifier is produced in Whistler. Available multimeter R× 100 block log, the tone head end lead welding, so as not to form a loop; then switch on the "ON" position, if placed in the "OFF" position, rather than the center line and shielded cable shorted, will complete the circuit, impact test, multimeter plug Center-metal case with microphone, should not be on the core wire is not connected with handheld metal parts, preventing the human body sensors, but should be a metal barrel shell and plug shield wire terminals, so that the handheld's touchIs the power amplifier section of the grounding, the whistle will not occur.
Fourth, electret microphone (MIC)
The multimeter Rotary to R× 100, red table Rod received microphone metal shielding network, black table Rod received its core wire, equivalent to internal MOSFET drain plus positive voltage, multimeter pointer refers to a certain scale, then inflatable microphone, if the pointer is no reaction, may wish to use table Rod swap detection, if the microphone is still no reaction when blowing, you can view electret leakage damage. If the microphone has a certain blowing, pointer amplitude of oscillation, electret microphone intact. If a direct test handset pin no resistance, internal electret as open; if the resistance is zero, as in a very short description; if electret intact, you should carefully check whether external lead wire, short circuit, open circuit.