WANTED: Good Source of Electronics Theory

24 PDFs that make up a pretty fair basic electronics course, fairly current as of 2003.

US Navy Electricity and Electronics Training Series

Module 1 - Introduction to Matter, Energy, and Direct Current Module 2 - Introduction to Alternating Current and Transformers Module 3 - Introduction to Circuit Protection, Control, and Measurement Module 4 - Introduction to Electrical Conductors, Wiring Techniques, and Schematic Reading Module 5 - Introduction to Generators and Motors Module 6 - Introduction to Electronic Emission, Tubes, and Power Supplies Module 7 - Introduction to Solid-State Devices and Power Supplies Module 8 - Introduction to Amplifiers Module 9 - Introduction to Wave-Generation and Wave-Shaping Circuits Module 10 - Introduction to Wave Propagation, Transmission Lines, and Antennas Module 11 - Microwave Principles Module 12 - Modulation Principles Module 13 - Introduction to Number Systems and Logic Circuits Module 14 - Introduction to Microelectronics Module 15 - Principles of Synchros, Servos, and Gyros Module 16 - Introduction to Test Equipment Module 17 - Radio-Frequency Communications Principles Module 18 - Radar Principles Module 19 - The Technician's Handbook Module 20 - Master Glossary Module 21 - Test Methods and Practices Module 22 - Introduction to Digital Computers Module 23 - Magnetic Recording Module 24 - Introduction to Fiber Optics

Do you have an oscilloscope?? If you do, it is a simple matter of tracking the signal on the good side and comparing it to the "lack of signal" in the bad side, stage by stage.

The training source given by the 2nd poster looks to be great!!!.

Bob Hofmann

Arny gave you a list of some teaching materials for electronics theory, however, most of them seem to focus on more advanced systems theory. I don't know to what level these texts assume the reader has progressed. It's been so long since I looked at a basic theory text that I can't recommend any without a bit of searching. Perhaps another reader can be of more assistance.

If your focus is on solid state equipment, then you'll need to focus your studies on theories of transistor circuits. The most basic component that you'll need to study hard and really understand is, of course, the transistor.

In reference to your tape deck problem, If you could think about how the various voltages in the circuit are derived, then it might be a little clearer. Remember that transistors are current operated devices, that is, a small current through the base-emitter of the transistor modifies the current between the collector and emitter. In normal linear circuits, a transistor's B-E junction is forward biased, while the B-C junction is reverse biased. Forward-biased: current flows; reverse-biased: no current flows.

Assuming silicon transistors, the B-E junction is forward-biased with a voltage of approximately 0.5 to 0.7 volts between the base and emitter. Always use the emitter as a reference point for voltage measurements around a transistor. For an NPN device, the base is positive with reference to the emitter. For a PNP, the base is negative to the emitter.

In your tape circuit, the big clue to the problem is lack of any voltage at the collector of Q205. Q205 must be turned on, at least partially, in order for any voltage to appear at its collector (which is showing no voltage). It is the only path that can supply the current to Q203 is through the E-C circuit of Q205. If Q205's B-E is properly forward biased, current should flow through the C-E circuit. Measure the B-E voltage of Q205. If it's in the vicinity of 0.5 - 0.7 volts, then the transistor should be conducting current from its emitter to its collector. If the voltage there is less than that, then the transistor can't conduct, thereby shutting off the C-E circuit.

If the transistor's B-E junction is properly forward biased, then it should be conducting. If it isn't conducting, then the transistor is either open or there is another fault, and further troubleshooting is needed. My bet on your tape deck's fault is on Q205. Let me know if that fixes it.

Hope this helps you get started,

-- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address)

There's something amiss with the biasing of the output emitter-follower stage. The voltage on the base of Q208 should be about 1.2V less (not 0.2V less I think that 6.8V should be 5.8V) than the voltage on the base of Q207. That suggests possibly zero or very low current in Q205's collector circuit. Suggest you measure the voltage across the 12k connected to Q205's base-emitter.

Graham

any

the

Could you repeat this part, please?

There is no Q203 in this circuit.

Thanks for your help!

You are ABSOLUTELY CORRECT. I took another good, hard look at the service manual schematic (very fuzzy), and the base voltage of Q208 is indeed +5.8V.

How did you deduce this?

I'm not sure about the 12K resistor across Q205's base-emitter. I will take a voltage measurement across that resistor and post it here.

Yes, you're right... I should have said The only path that can supply the current to Q206 is through the E-C circuit of Q205. The voltages around Q205 are the clues to your problem. Find out why Q205 isn't conducting and you'll find the problem.

--
Dave M
MasonDG44 at comcast dot net  (Just substitute the appropriate characters in the 
address)

Some people are like Slinkies.  Not really good for anything, but they bring a 
smile to your face when pushed down the stairs.

FWIW, the base voltage of Q205 is +11.09V. This was measured at the junction of the base terminal and the 12K resistor.

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Q205 is biased just fine. It has nearly 5V emitter to collector, There is a problem around Q206, though. This transistor provides thermal regulation for the quiescent current in the output stage. If you look at the base and emitter voltages, you will see that it has become reverse biased by 0.4V and there is possibly no voltage difference between collector and emitter. It is not easy to see why this might be. What is the voltage on the collector of Q208? It is misbiased right now, possible by a bad Q206.

Just looking at the basic bias conditions, I would say

Q204 ok Q205 ok Q206 problem - maybe C-E short Q207 ok Q208 reverse biased B/E

So whatever is wrong, I think it is happening down around that bottom right hand corner.

Perhaps more to the point, how do all these points measure on the good channel?

--
Pearce Consulting
http://www.pearce.uk.com

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No, the voltages around Q205 aren't OK, and that appears to be at the crux of the problem. Remember that the OP said that measurements on his schematic that were marked with an asterisk (*) were nearly 0V. That means that Q205's collector is at 0V, rather than 7V, so it isn't conducting. The question remains, and we're still wating for the OP's response, what is the B-E voltage of Q205? If it's normal, then Q205 is probably bad; if it's not normal (less than 0.5V), then Q205, or something around it, is the culprit.

Where's the OP?

==============

Dave M

Never take a laxative and a sleeping pill at the same time!!

Don:

I'm not sure, but you might be reading my schematic incorrectly.

There SHOULD be +7V at Q205's collector...but right now, there is only

20 - 30mV.

The +7V figure is what the service manual indicates is the "proper" voltage for Q205's collector.

Regarding Q206, the actual voltages for the base and emitter are both currently reading just a few millivolts, just like the collector of Q205.

The indicated voltages for Q206 are, once again, merely from the service manual, and the figure for the emitter was written incorrectly. The proper voltage for the emitter of Q206 is +5.8V.

alt.binaries.e-book.technical

Because there should be 2 Vbe's difference betwen those 2 points (to turn on the complementary emitter follower stage).

That will be helpful.

Graham

That suggests a Vbe of 0.81V in which case Q205 *ought* to be well turned on and conducting strongly but it isn't.

Replace Q205.

Graham

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for any

through the

NO. Those are the service manual values. Q205's collector is actually almost at ground potential, i.e. not conducting.

Graham

In order to troubleshoot *discrete* transistor circuits that may be a tall order. They don't even teach this stuff much at college or Uni any more !

Graham

That's an expensive way - although of course a good one. For many years I managed with a small battery amp and speaker.

--
*White with a hint of M42*

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

I had this text in one of my engineering courses at the University of South Florida (Tampa) and in my opinion it would be an excellent book for the purpose you have in mind:

@BOOK{sedra, title = "{Microelectronic Circuits}", author = "Adel~S.~Sedra and Kenneth~C.~Smith", publisher = "Saunders College Publishing", edition = "third", year = "1991"}

--
%  Randy Yates                  % "My Shangri-la has gone away, fading like 
%% Fuquay-Varina, NC            %  the Beatles on \'Hey Jude\'" 
%%% 919-577-9882                %  
%%%%            % \'Shangri-La\', *A New World Record*, ELO
http://www.digitalsignallabs.com

OK, the plot thickens somewhat...

Some of you have told me that, in my non-functioning amplifier circuit, the most likely culprit was Q205.

I have replaced Q205 and the circuit STILL doesn't work. It is exactly the same as before.

There is only 131.1mV on the collector of Q205, despite +11.09V on its base and +11.59V on its emitter.

Aaargh!