Sir gudday may i know the value op pre driver transistor to replace A940

pls check burnt resistors, if ceramic it's value is .25 0hms 5 watts, if big carbon film resistor it's value is 10 ohms 3 watts. check also power transistors A1941 & C5198. also check driver transistor A940 & C2073

Download and Install the A940 All-In-One Printer Driver ' Dell here is the site you need to get your drivers if you need more help let me know

hi.
Did you checked balanced impedance?load speaker impedance vs PA output?or PA might over driven,causing a trouble on the pre-amp to power amp circuits and components damage,
need to recheck related components on the pre-driver up to main output section,

Note: That,blowing of fuses with the same rating is an indication of trouble/shorted in a circuits that driven on it,

Thanks and good luck

microhit

The driver circuits should be just before the outputs in the circuitry. The easiest way to check this circuit is to remove the outputs and turn on the unit. Measure each of the transistor pads relativce to ground for DC voltage. You should see the following: B+,0.6V (or 1.1V), and 0V on one transistor and negative values on its compliment. If you have questions, measure the pads and post the measurements here. In some cases the output transistor needs to be in place to get the values above, so if yours don't measure that way, just post what you get and we'll continue from there.

Dan

Good day sir, there are several reason why the amplifier hums, but lets go to the common ones,

1. The main power amplifier is defective. Does the volume control affect the loudness of the hum? If no, possibly replace your main amplifier IC. if its transistorized, check the two push pull amp. for shorts.
2. If Yes, check for shorted audio cables. just maker sure you are using a good audio cable. or
3. The pre-amp IC is defective, usually op-amps. try replacing them one at a time. these requires unsoldering and soldering.
4. If you want to find the faulty part, you may need to trace a signal, you may need the folowing, an audio source, sine wave generator, an oscilloscope, or a portable amplifier. This method requires you to be techie. Feed the input with the audio source (disconnect first the speakers so that the hum will not bother you.) check the output of each stage, from preamp to power amp. identifying where the heck the signal dissapper. and where the start humming appears.

The third one requires a lot of work, just bring it to a service center.
Hope this helps, feel free to ask again, let me know your progress. Thanks

Hello, this problem is solved and how?
I have the same problem on HF and VHF 30Watt max output

1.8 MHz-20M 0-5Watt
10M 25 Watt
6M-30Watt

2M-25Watt

70cm 42Watt is ok
23cm 10Watt is ok

thanks

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An audio amplifier is a general term that applies to any amplifier specifically designed to cover the audio spectrum, and usually referres to power amplifiers (of any power from micro headphone amps (like the headphone audio amplifier circuit in an ipod) . to power amps like the ones used at rock concerts that are several thousand watts).

An OP-AMP is an Operational Amplifier, which refers to a type of amplifier circuit. Op-Amps can amplify audio, but are not restricted to it. They are used in many things from audio circuitry to signal conditioning, and sensing from all kinds of equipment from seismometers, to light sensors, temp sensors, insturmentation amps, lab amps... RF amps etc...

There are many many different types of op-amps that are designed for many different applications. Mostly the parameters are frequency response, gain, and input/output impedance.

Op-amps usually come in an IC package of some sort. The most common are 8 pin DIP package types.

Op-amps do NOT handle power. (although there are some hybrid power op-amps available, they are specialty devices) The term op-amp refers to the ability of the amplifier to be manipulated mathematically by external values. (i.e. resistors set up to add, subtract, or multiply the value of the input signal) Hence the term OPERATIONAL amp, because it is performing mathematical operations on the signal. (They were first used in analog computers, allowing the voltages to be added, subtracted, and such, and displaying the resultt by directly reading the voltage value).

They handle only small signals, and require being followed by a POWER amp to do anything useful, such as drive a spleaker, or a relay, or a transducer.

For your question, most all audio amps consist of stages.

There is an input/pre-amp stage (this is usually where the eqalization, signal processing, and bass/trebel tone controls are implelented) and a power amp (output) stage that takes the signal fromthe pre-amp and raises the voltage and current to a sufficient level to drive speaker.

The input/pre-amp stage is most usually composed of a series of op-amps. Op amps also are responsible for the bass/trebel control, and the EQ.

There will most usually always be several Op-Amps in every Audio Amp.

You've replaced the pre driver, the drivers and finals. Set bias and still low output. The pre driver is the same transistor used as the tx exciter transistor on other pcb chassis on bottom of radio. Follow the gray coaxial wire from the pre driver on the RF circuit board back to the tx/rx i.f. Circuit board. The gray coax cable plugs right next to the tx exciter transistor on this pcb. Again it's on a different pcb all together and on the bottom of the radio and also. Replace it! And check for open bias or emitter to ground chip resistor next to it. You will get your drive back. Very few rigs have I seen the actual Finals blown in the mosfet or the bipolar version. Just the driver stage with a week pre driver and the SMT "pre" pre driver on the same RF pcb. And the tx exciter on the other pcb.

check all op amps for correct voltage swing +-should be equal,test output of op amps no voltage should be present, use chasis gnd as tester neg.check voltage regulation especially 12v or 15v +-.note some amps show unequal led indications when only 1 channel connected to a load.I will try to get some more info on this specific amp because i don't know this circuit well,keep in touch as you update though.

Driver ICs or transistors,op-amps that create the idle bias circuit,the protection circuit, the power supply. You should have a schematic of this unit and know how to check the solid state devices for shorts. GOOD lUCK