Re: WANTED: Good Source of Electronics Theory

On Apr 19, 2:40=A0pm, EADGBE <hwbossh...@[EMAIL PROTECTED]
> wrote:
> I am a home hobbyist who enjoys restoring vintage stereo equipment. =A0I
> have a good working knowledge of electronic components and what they
> do. =A0I have decent test equipment and good soldering skills, and most
> of the time I am able to track down and repair a particular problem.
>
> However, I do feel that I need to know more about the theory behind
> electronic circuits in order to improve my troubleshooting skills.
>
> Sometimes I find myself looking at a schematic and thinking, "Boy, I
> wish I knew more about what is supposed to be happening in this
> circuit!"
>
> Can anyone point to any good books or online sources where I can learn
> more about how to analyze schematics and recognize what is supposed to
> be happening?
>
> CASE IN POINT: I am attempting to repair a tape deck. =A0One channel
> (the right channel) of the headphone amplifier doesn't work. =A0The tape
> deck has perfect output through the line out jacks.
>
> Here is the schematic for one of the channels of the tape deck's
> headphone amp:
>
> http://i240.photobucket.com/albums/ff58/eadgbe123/amplifier.jpg
>
> I have reproduced the schematic in my own handwriting because the
> downloaded schematic was too fuzzy to scan. =A0I *think* I have copied
> everything correctly.
>
> I cannot figure out why this particular circuit isn't working
> correctly. =A0I have checked each component--and even replaced a few
> transistors even though all transistors tested fine--but nothing is
> improving.
>
> I have tested all of the electrolytics with my ESR meter and they all
> check out OK.
>
> I have checked all resistors and none of them have opened up or "gone
> high".
>
> Notice that there are some "typical" expected voltages indicated at
> certain points. =A0These "typical" voltages have come right out of the
> service manual. =A0All of the voltages marked "OK" are...well...OKAY.
> But the three voltages marked with a star (*) are NOT okay...they are
> all just a few millivolts each--around 20 to 30mV.
>
> All capacitors are electrolytic with the exception of the 4.7pF
> capacitor, which is ceramic.
>
> All resistors are 1/4 watt. =A0If there is no "K" after the number, then
> that is the amount of actual ohms it has.
>
> For the record, I replaced Q204, Q206, and Q208 but still got exactly
> the same results.
>
> What am I overlooking?

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