a power supply filter capacitor value becomes too low.
a power supply filter capacitor value becomes too low.
This being one of danny's threads, I doubt he's talking about audio amplifiers. Unfortunately he didn't say what sort of circuit he is talking about, or what voltage in the circuit is fluctuating.The output voltage of an amplifier...
Unfortunately he didn't say what sort of circuit he is talking about, or what voltage in the circuit is fluctuating.
In this case though, I thing RANDOM fluctuations are what the question refers to and danny davis is asking how to troubleshoot it. There is no single answer in that case but the general approach would be to look for clues that narrow down the area of fault and then work backwards toward the start of the circuit to see which stage intruduces the fluctuation. For example, if it was a stereo amplifier the first test should be to see if one or both channels exhibited the problem. If it's only one it would eliminate the power supply and any other circuitry that was common to both chanels. Then work from where the fluctuation can be measured to earlier stages in the circuit, if the output of a stage fluctuates but the one before it is stable, that stage is the faulty one. There is a lot of 'gut feeling' in faultfinding, it isn't a set solution every time and with complex IC designs there is sometimes no option but to substitute parts or use a 'trial and error' tactic.
Yes of course, this happens. The problem with this thread is, that the OP is essentially guessing a transistor or IC is causing the fluctuations, but he didn't tell why he comes to the conclusion.They exist Audioguru - believe me!
There can be several failure mechanisms including:
destruction or damage to part of the si/ge crystal due to overheating or mechanical stress.
fracture at the welds due to stressing the pins or repeated hot/cold cycles.
corrosion, particularly along the wire of the pins, it sometimes reaches as far as the junctions. (Devices running hot can actually be more reliable because of this)
impurites in the junction materials
metal migration across pins and to the can if its made of metal.
because what?No, its the transistor for sure because I have to change the bad fluctuating transistors
The base to emitter voltage is 0.7V in circuit.the base to emitter for an npn transistor is not. 7 volts in circuit is this true?
Yes, that's right.For pnp transistors u have to reverse the probes to get the. 7 volts?
Yes. The circuit must be powered on. Set the multimeter to read voltage then connect one probe to the base and the other probe to the emitter.Is there any way to measure the transistors .7 volts across the base to emitter , when the transistor is in circuit?
That's another way to do it. Both methods should work.I should turn the circuit OFF no power on and use the DVM diode mode when testing a transistor base to emitter in circuit?
You can measure the 0.7 volts from base to emitter of a PNP transistor the same way as for an NPN transistor. The only difference is you have to reverse the probes.You can't measure the .7 volts when a transistor is PNP because it's only .7 volts from base to emitter using NPN transistors, is that right?
the base to emitter for an npn transistor is not. 7 volts in circuit is this true?
The base to emitter voltage is 0.7V in circuit.
More or less. It may be 0.6V or 0.8V, or somewhere in between.Even when the base has signal on the input of the transistor? it will still be 0.7 volts?
Yes, the resistors bias the transistor to energize it, but they do that by putting about 0.7V between the base and collector. So the DC offset from the resistors is the 0.7V that switches the transistor on.I thought the resistors around the transistor biased the transistor and energized the transistor when an input signal was applied to the base or input of the transistor , so testing the transistors base to emitter you won't get 0.7 volts because of the DC offset from the resistors that are biasing the transistor right? plus the circuit is powered on
PNP transistors can be used for all the same things as NPN transistors - amplifiers, oscillators, constant current sources etc.What else have you seen circuits using PNP transistors for?
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