Signal tracing deals with a way of diagnosing where there’s a fault in any audio system. It isn’t as great as the oscilloscope; however it is a less-expensive alternative which could be very useful in different scenarios.
The idea here is that a signal is applied to what is not working, and then the signal is traced through a circuit till this audio disappears. Also, it isn’t useful in power amplifier stages that are directly coupled. This is due to the fact that when there’s one fault in a part of a circuit, this could lead the whole amplifier not to function anymore.
What Does a Signal Tracer Mean?
Signal tracers can be described as amplifiers which could detect RF and audio signals and then play it through the in-built speaker. When you trace signals for each stage via the radio then you will discover the problems causing it to play poorly or not play at all. Whenever you know the radio parts that are functioning properly then you may concentrate on the suspect components and stages.
For instance, whenever you hear the local radio stations via the signal tracer that is connected onto the volume control ‘s center tap, and then sound is absent from the speaker of the radio, then you’ll know that the tuning circuits, antenna, detector, and IF section are all functioning properly. Then you can focus all your attention on the earphone jack, speaker, audio circuitry.
As seen in working radios, you would have the ability of tracing forward via the signal tracer strength and then hear the station of the radio at the outputs and inputs of it’s IF amplifiers and then to the input of the audio amplifier.
Also, the signal tracers meant for circuit and service design work are packaged to take lots of forms with time from the multi-purpose large bench equipment to shirt pocket tracers having a Pen’s shape.
Majority of the signal tracers utilized for all service work during the 1930s made use of vacuum tubes and were known to take up so much space.
What are the Functions of the Signal Tracer?
The signal tracers are utilized for the trouble shooting of any misbehaving receivers. Also, signal generators are useful for troubleshooting and adjusting receivers.
The utilization of signal generators for the adjustment of receivers deserves personal presentation. The author has been able to create a document for the adjustment of receivers. This presentation will cover just the troubleshooting.
Whether you are making use of a signal generator or signal tracer for your troubleshooting, you will have the same goal. This is the isolation of faults to one receiver stage. Practically speaking, this has to do with isolating the malfunction to those components linked to a single unit or tube inside a tube. Immediately you can identify any faulty stage, the activity of troubleshooting changes it’s style to locate one defective component that usually needs different equipment.
Furthermore, whatever equipment you decide to work with, make sure that you work with a reliable safety practice. This indicates making use of the line isolation transformer, a DC blocking capacitor on the test leads of the signal generator, as well as keeping one hand behind when probing the circuits with high voltage.
Several signal tracers give access to its output speakers and transformers to serve as a temporary substitute. This could be very helpful when there is no speaker because it is sent for repair or it is not just convenient for use like in the console radio.
Several signal tracers have a NOISE mode that applies a limited voltage which is around 50 VDC into the probe. Also, the author found this important for the repair of any shorted tuning condenser. You can remove this tuning condenser out of the chassis and then apply the signal tracer’s voltage into it, inside the darkened room. In addition, as you rotate this tuning condenser, sparks will show up the contact points between the vanes.
What Does Signal Tracer Schematic Mean?
Signal tracer schematics, which is also called schematic diagram, represents the signal tracer elements making use of graphic, abstract symbols instead of using realistic pictures. Usually, this schematic omits all the details, which aren’t relevant to whatever information this schematic should convey, and might add some unrealistic elements which helps in comprehension. For electronic circuit diagrams, the symbols’ layout might not look like the circuit’s layout.
Furthermore, during the creation of the signal tracer schematic, it is very important that you ensure you’re illustrating the circuit with the appropriate abstraction level. Also, if you are only making efforts to convey a high-level concept, then the napkin schematic may fail to do this truck. This is why of you have to create a specific schematic for simulation, then you have to be clear regarding the signal sources, power sup[p[lies, component values, and more.
Using the Signal Tracer Schematic
Take for example that you are beginning with a fully dead channel 6506 radio. Now, if you’ll be working with mid-century transistor radios, then you have a great chance one of the quick fixes will be able to start playing again. You should try this before any signal tracing or before aligning a radio.
Next, connect this radio to bench power supplies that have been regulated, which you’ve set to the right polarity and voltage, or just load it using fresh batteries.
Bring your ear near the speaker of the radio like you can. Then switch on the radio. Did you get a pop or click sound from your speaker? If you don’t hear a silent click coming from the speaker of the radio whenever the radio is switched on, then make use of the voltmeter just to be sure power is getting inside the board. Broken speaker wires or battery, bad battery contact, broken PCB trace, as well as power switches that are faulty are well-known problems which may halt your progress.
Also, if you would be making use of a bench supply in addition to an ammeter, check if the drawn current falls within the stated range. Next, connect the ground lead of the signal tracer to the ground of the radio. Determining the ground point from the schematics is easy.
Set your signal tracer into the audio input and when the tracer comes with volume control, then set it mid-way. In addition, place your input-probe on the radio volume control’s center contact. Then pay close attention to the speaker of the tracer for signals. Then adjust the volume control of the tracer where necessary.
More on How to Use the Signal Tracer Schematic
If you are lucky you will hear an atmospheric static, as well as local radio stations whenever you tune anyone in. When you listen to any local station, it means that the tuning circuitry, antenna, IF detector and antenna, mixer/oscillator, are all functioning properly. At this point, you will not be able to know if any of these stages are working effectively and efficiently. Also, this tells you there’s a problem with the audio stage.
Now, things you should suspect include damaged traces, electrolytic capacitors, dirty or clogged volume controls, faulty and out-of-spec transistors, speakers, transformers, etc.
Immediately the problem with the audio has been solved, determining if the performance as a whole is acceptable. Also, check if the audio is undistorted and loud? Can stations be received at the broadcast band’s low and high ends? Is there a reasonably accurate dial pointer? If you can answer yes to all these, then you are set.
If this isn’t the case, re-trace the signal listening for any increase in the levels of a signal from one stage to the other. Whenever a faulty stage is suspected, compare the measurements with all those that have been listed in service docs in order to isolate the issue further.
Signal Injecting and Tracing Tips
Familiarize yourself with signal tracing on a known-good radio so as to calibrate the test gear as well as yourself. This way is a great one to help you understand the right settings to make use of as well as how the sound of a normal set is, whenever it is traced.
Old PCBs feature a protective coating on them which helps in the prevention of test probes from creating the right electrical contact. Make use of probes having pinpoint tips.
Whenever you hear any rushing static sound when the radio is turned on, and have the ability to control this noise using its volume control, then the section for the audio is fine. Next, you check the IF as well as other sections on the left hand side of the signal tracer schematic.
Conclusion
Understanding and using the signal tracer schematic is very important. Signal tracer schematics, which is also called schematic diagram, represents the signal tracer elements making use of graphic, abstract symbols instead of using realistic pictures. Furthermore, during the creation of the signal tracer schematic, it is very important that you ensure you’re illustrating the circuit with the appropriate abstraction level.
