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WANTED: Good Source of Electronics Theory
WANTED: Good Source of Electronics Theory
I am a home hobbyist who enjoys restoring vintage stereo equipment. I
have a good working knowledge of electronic components and what they
do. I 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. One channel
(the right channel) of the headphone amplifier doesn't work. The 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:
* 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. I *think* I have copied
everything correctly.
I cannot figure out why this particular circuit isn't working
correctly. I 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. These "typical" voltages have come right out of the
service manual. All 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. If 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?
I am a home hobbyist who enjoys restoring vintage stereo equipment. I
have a good working knowledge of electronic components and what they
do. I 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. One channel
(the right channel) of the headphone amplifier doesn't work. The 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:
* 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. I *think* I have copied
everything correctly.
I cannot figure out why this particular circuit isn't working
correctly. I 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. These "typical" voltages have come right out of the
service manual. All 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. If 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?
Re: WANTED: Good Source of Electronics Theory
"EADGBE" <hwbosshoss@comcast . net > wrote in message
news:d8647727-1ae7-4fbd-96f7-1f9ffea3b0b9@e67g2000hsa.googlegroups . com
> I am a home hobbyist who enjoys restoring vintage stereo
> equipment. I have a good working knowledge of electronic
> components and what they do. I 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?
* jacquesricher . com /NEETS/
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
"EADGBE" <hwbosshoss@comcast . net > wrote in message
news:d8647727-1ae7-4fbd-96f7-1f9ffea3b0b9@e67g2000hsa.googlegroups . com
> I am a home hobbyist who enjoys restoring vintage stereo
> equipment. I have a good working knowledge of electronic
> components and what they do. I 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?
* jacquesricher . com /NEETS/
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
Re: WANTED: Good Source of Electronics Theory
* w w w .amazon . com /Electronics-Principles-Applications-MultiSIM-CD-ROM/dp/0078309778/ref=sr_1_2?ie=UTF8&s=books&qid=1208642336&sr=1-2
* w w w .amazon . com /Electronics-Principles-Applications-MultiSIM-CD-ROM/dp/0078309778/ref=sr_1_2?ie=UTF8&s=books&qid=1208642336&sr=1-2
Re: WANTED: Good Source of Electronics Theory
On Apr 19, 2:40 pm, EADGBE <hwbossh...@comcast . net > wrote:
> I am a home hobbyist who enjoys restoring vintage stereo equipment. I
> have a good working knowledge of electronic components and what they
> do. I 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. One channel
> (the right channel) of the headphone amplifier doesn't work. The 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:
>
> * 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. I *think* I have copied
> everything correctly.
>
> I cannot figure out why this particular circuit isn't working
> correctly. I 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. These "typical" voltages have come right out of the
> service manual. All 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. If 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
On Apr 19, 2:40 pm, EADGBE <hwbossh...@comcast . net > wrote:
> I am a home hobbyist who enjoys restoring vintage stereo equipment. I
> have a good working knowledge of electronic components and what they
> do. I 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. One channel
> (the right channel) of the headphone amplifier doesn't work. The 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:
>
> * 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. I *think* I have copied
> everything correctly.
>
> I cannot figure out why this particular circuit isn't working
> correctly. I 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. These "typical" voltages have come right out of the
> service manual. All 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. If 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
Re: WANTED: Good Source of Electronics Theory
In article
<e3095ed1-b4b0-4f82-930c-fb13c1538056@59g2000hsb.googlegroups . com >,
hr(bob) hofmann@att . net <hrhofmann@att . net > wrote:
> 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.
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.
In article
<e3095ed1-b4b0-4f82-930c-fb13c1538056@59g2000hsb.googlegroups . com >,
hr(bob) hofmann@att . net <hrhofmann@att . net > wrote:
> 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.
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.
Re: WANTED: Good Source of Electronics Theory
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)
Some people are like Slinkies. Not really good for anything, but they bring a
smile to your face when pushed down the stairs.
"EADGBE" <hwbosshoss@comcast . net > wrote in message
news:d8647727-1ae7-4fbd-96f7-1f9ffea3b0b9@e67g2000hsa.googlegroups . com ...
>I am a home hobbyist who enjoys restoring vintage stereo equipment. I
> have a good working knowledge of electronic components and what they
> do. I 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. One channel
> (the right channel) of the headphone amplifier doesn't work. The 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:
>
> * 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. I *think* I have copied
> everything correctly.
>
> I cannot figure out why this particular circuit isn't working
> correctly. I 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. These "typical" voltages have come right out of the
> service manual. All 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. If 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?
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)
Some people are like Slinkies. Not really good for anything, but they bring a
smile to your face when pushed down the stairs.
"EADGBE" <hwbosshoss@comcast . net > wrote in message
news:d8647727-1ae7-4fbd-96f7-1f9ffea3b0b9@e67g2000hsa.googlegroups . com ...
>I am a home hobbyist who enjoys restoring vintage stereo equipment. I
> have a good working knowledge of electronic components and what they
> do. I 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. One channel
> (the right channel) of the headphone amplifier doesn't work. The 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:
>
> * 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. I *think* I have copied
> everything correctly.
>
> I cannot figure out why this particular circuit isn't working
> correctly. I 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. These "typical" voltages have come right out of the
> service manual. All 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. If 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?
Re: WANTED: Good Source of Electronics Theory
On Apr 19, 5:04 pm, "DaveM" <masondg4...@comcast99 . net > wrote:
>
> 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.
Could you repeat this part, please?
There is no Q203 in this circuit.
Thanks for your help!
On Apr 19, 5:04 pm, "DaveM" <masondg4...@comcast99 . net > wrote:
>
> 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.
Could you repeat this part, please?
There is no Q203 in this circuit.
Thanks for your help!
Re: WANTED: Good Source of Electronics Theory
"EADGBE" <hwbosshoss@comcast . net > wrote in message
news:67717a13-6234-4847-aa72-bb57663b9fcb@s50g2000hsb.googlegroups . com ...
> On Apr 19, 5:04 pm, "DaveM" <masondg4...@comcast99 . net > wrote:
>>
>> 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.
>
> Could you repeat this part, please?
>
> There is no Q203 in this circuit.
>
> Thanks for your help!
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.
"EADGBE" <hwbosshoss@comcast . net > wrote in message
news:67717a13-6234-4847-aa72-bb57663b9fcb@s50g2000hsb.googlegroups . com ...
> On Apr 19, 5:04 pm, "DaveM" <masondg4...@comcast99 . net > wrote:
>>
>> 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.
>
> Could you repeat this part, please?
>
> There is no Q203 in this circuit.
>
> Thanks for your help!
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.
Re: WANTED: Good Source of Electronics Theory
FWIW, the base voltage of Q205 is +11.09V. This was measured at the
junction of the base terminal and the 12K resistor.
FWIW, the base voltage of Q205 is +11.09V. This was measured at the
junction of the base terminal and the 12K resistor.
Re: WANTED: Good Source of Electronics Theory
EADGBE wrote:
> FWIW, the base voltage of Q205 is +11.09V. This was measured at the
> junction of the base terminal and the 12K resistor.
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
EADGBE wrote:
> FWIW, the base voltage of Q205 is +11.09V. This was measured at the
> junction of the base terminal and the 12K resistor.
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
Re: WANTED: Good Source of Electronics Theory
On Sat, 19 Apr 2008 14:36:36 -0700 (PDT), EADGBE
<hwbosshoss@comcast . net > wrote:
>On Apr 19, 5:04 pm, "DaveM" <masondg4...@comcast99 . net > wrote:
>>
>> 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.
>
>Could you repeat this part, please?
>
>There is no Q203 in this circuit.
>
>Thanks for your help!
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
* w w w .pearce.uk . com
On Sat, 19 Apr 2008 14:36:36 -0700 (PDT), EADGBE
<hwbosshoss@comcast . net > wrote:
>On Apr 19, 5:04 pm, "DaveM" <masondg4...@comcast99 . net > wrote:
>>
>> 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.
>
>Could you repeat this part, please?
>
>There is no Q203 in this circuit.
>
>Thanks for your help!
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
* w w w .pearce.uk . com
Re: WANTED: Good Source of Electronics Theory
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.
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.
Re: WANTED: Good Source of Electronics Theory
Don Pearce wrote:
> On Sat, 19 Apr 2008 14:36:36 -0700 (PDT), EADGBE
> <hwbosshoss@comcast . net > wrote:
>
> >On Apr 19, 5:04 pm, "DaveM" <masondg4...@comcast99 . net > wrote:
> >>
> >> 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.
> >
> >Could you repeat this part, please?
> >
> >There is no Q203 in this circuit.
> >
> >Thanks for your help!
>
> Q205 is biased just fine. It has nearly 5V emitter to collector,
NO. Those are the service manual values. Q205's collector is actually almost at ground
potential, i.e. not conducting.
Graham
Don Pearce wrote:
> On Sat, 19 Apr 2008 14:36:36 -0700 (PDT), EADGBE
> <hwbosshoss@comcast . net > wrote:
>
> >On Apr 19, 5:04 pm, "DaveM" <masondg4...@comcast99 . net > wrote:
> >>
> >> 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.
> >
> >Could you repeat this part, please?
> >
> >There is no Q203 in this circuit.
> >
> >Thanks for your help!
>
> Q205 is biased just fine. It has nearly 5V emitter to collector,
NO. Those are the service manual values. Q205's collector is actually almost at ground
potential, i.e. not conducting.
Graham
Re: WANTED: Good Source of Electronics Theory
EADGBE wrote:
> Notice that there are some "typical" expected voltages indicated at
> certain points. These "typical" voltages have come right out of the
> service manual. All 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.
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
EADGBE wrote:
> Notice that there are some "typical" expected voltages indicated at
> certain points. These "typical" voltages have come right out of the
> service manual. All 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.
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
Re: WANTED: Good Source of Electronics Theory
On Apr 19, 5:17 pm, Eeyore <rabbitsfriendsandrelati...@hotmail . com >
wrote:
>
> 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.
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.
On Apr 19, 5:17 pm, Eeyore <rabbitsfriendsandrelati...@hotmail . com >
wrote:
>
> 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.
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.
