And the price of phone is reasonable and as low as possible

phone contains the charger, car charger and jammer.
Weld parts due to the role of the force at time of press sealing off, causing the phone to shut down. Maintenance, in a targeted manner to strengthen key lower part of the integrated circuit or component welding generally solve the problem. The caller calls shutdown shutdown is the mobile phone can boot, network, can call the phone ringing sound when a call, the phone shut down. This failure appears to be complex, is actually very simple, calls will be shut down? Is nothing more than ringing sound caused. Ring a ring, why would shut down? This is because a lot of ring work when battery voltage BATT + direct power supply, when the ringing of leakage, it will result in phone calls shutdown. phone has the dynamic jamming range.The company should monitor and supervise the production process of phone.Therefore, mobile phone repair personnel on hand should have a containing current, voltage meter multi-function round-trip run power, for maintenance use. Maintenance ammeter connected in series in the mobile phone power circuit, by measuring the total current of the mobile power supply circuit to determine the fault location. 1, press the power button, the ammeter pointer does not move or logo placed, the phone can not boot. This phenomenon is the cause boot signal circuit or power IC does not work. 2, press the power button, there are dozens of ma current, then back to zero, the phone can not boot. There are dozens of ma currents, indicating that the basic failure of the power part of the multi-clock circuits, logic circuits or software is not normal cause. The feedback of the customer is very important for phone .And the price of phone is reasonable and as low as possible
If the current minor move, the clock circuit should be normal, general software failure, if not swing, failure or CPU clock circuit did not work properly. In addition, dozens of ma current stops moving, press the switch button no response, in most cases for a software failure. Does not boot, the boot key ammeter pointer indicates current 200ma or so pause immediately back to zero, which is a typical piece of code data confusion caused by the software does not boot. Phone power leakage (do not press the power button) there are 20 to about 30ma. The power part of the component short-circuit or damage. Press the power button, a large current, indicating that the power supply part of the short-circuit phenomenon, or the power amplifier part of component damage. The manufacturer has cut the price of phone .  Able to boot the standby current than normal. Showed that the load circuit component leakage. Remedy: power to the mobile phone, after 1-2 minutes with the back of which a component to feel hot, be replaced, in most cases, troubleshooting. 7, the phone is switched on to play 112, observed changes in the current, if the current change is normal, then the emission current is normal, in the absence of current changes, then the transmitter circuit does not work, if the current change is too large, a general description of the amplifier circuit is broken.

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Low Voltage Remote Mains Switch

This circuit allows a 240V mains appliance to be controlled remotely via low-voltage cabling and a pushbutton switch. The mains appliance (in this case, a light bulb) is switched with a suitably-rated relay. All of the electronics is housed in an ABS box located in proximity to the appliance. The pushbutton switch and plugpack are located remotely and can be wired up with 3-core alarm cable or similar. Cable lengths of 20m or more are feasible with this arrangement. When the switch (S1) is pressed, the input (pin 8) of IC1c is briefly pulled low via the 10mF capacitor, which is initially discharged.

The output (pin 10) immediately goes high and this is inverted and fed back to the second input (pin 9) via another gate in the quad NAND package (IC1d). In conjunction with the 1MW resistor and 470nF capacitor, IC1d eliminates the effects of contact "bounce" by ensuring that IC1c’s output remains high for a predetermined period. The output from IC1c drives the clock input of a 4013 D-type flip-flop (IC2). The flipflop is wired for a "toggle" function by virtue of the Q-bar connection back to the D input. A 2.2MW resistor and 100nF capacitor improve circuit noise immunity. Each time the switch is pressed, the flipflop output (pin 13) toggles, switching the transistor (Q1) and relay on or off. Note that all mains wiring must be properly installed and completely insulated so that there is no possibility of it contacting the low-voltage side of the circuit.

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Build a Low voltage regulators Circuit Diagram

These Low voltage regulators Circuit Diagram short-circuit protected regulators give 6, 7, and 9 V from an automobile battery supply of 13 V nominal; however, they will function just as well if connected to a smoothed dc output from a transformer/rectifier circuit. Two types are shown for both positive and negative ground systems. The power transistors can be mounted on the heatsink without a mica insulating spacer thus allowing for greater cooling efficiency. Both circuits are protected against overload or short-circuits. The current cannot exceed 330 mA.

Under normal operating conditions the voltage across R2 does not rise above the 500 mV necessary to turn Q2 on and the circuit behaves as if there was only Q1 present. If excessive current is drawn, Q2 turns on and cuts off Ql, protecting the regulating transistor. The table gives the values of Rl for different zener voltages.

 Low voltage regulators Circuit Diagram

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Low Noise Balanced Microphone Preamp Using TL071 IC

This is a simple design circuit which has very low noise, close to the theoretical minimum, high hum rejection and variable gain with a single rotary pot. The circuit design consists of differential compound pairs of transistors with a common mode (floating) gain control connecting the emitters of the pair. The compound pairs of 2N4403 and BC549s are far more linear than any single transistor. The circuit is differential in and out and therefore requires a balanced to unbalanced buffer to give suitable output for the next signal stages of a channel in a mixing desk. This is provided by a high performance op-amp differential gain stage, which can be a TL071 or similar IC of your choice. The stage has a gain of six or 15 dB and that sets the maximum input level at about 1.5 volts rms before clipping. This equals an SPL of over 150dB with a typical microphone. This is a figure of complete design for the circuit.


The operation of the circuit is input stage is configured for least noise and this has meant a non IC approach. There are some special ICs that can be used for microphone pre-amps, they contain a circuit like this one except fabricated on one chip. Components should all be readily available except for the 10 k ohm pot for the gain control. This needs to be a reverse log taper - or else use a multi-position switch with 6 dB gain steps covering the 60 dB range of the circuit. Make sure it is make before break. The +/-15 Volt power supply is important too, it must be regulated and low noise. If the usual voltage regulator ICs are used I recommend fitting a post filter consisting of a 10 ohm resistor and a 470 uF capacitor to remove any noise generated in the ICs.

Good quality components should be used with metal film resistors in the collectors and emitters of the input pairs for least noise. Where a resistor has significant DC voltage imposed on it in high gain circuits always use low noise types. Metal film resistors are about the best only bettered by wire wound which is a bit impractical. Avoid metal glaze, and very old carbon composition types. Also avoid bead tantalum capacitors, as they go leaky and crackle. They are just about the most fragile electronic components made. The 100nF capacitor (C6) should be mounted as close as possible to the op-amp supply pins - a ceramic cap is recommended for best bypass performance at high frequencies.

The design source is by Phil Allison

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