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Amplifier Problem - Revised Schematic
Amplifier Problem - Revised Schematic
In the interest of clarification, I have added some information to the
schematic of the tape deck headphone amp that I'm having problems
with.
Some circuit paths are now labeled:
* i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
As always, the points at which voltage readings are marked with a star
are NOT producing the voltage indicated. The +7V location is
measuring 131mV instead. The other two points where a star is
indicated are measuring between 20mV and 30mV (fluctuating slightly).
I am starting to think that a circuit OUTSIDE of this circuit might be
at fault, because NOTHING inside of this circuit seems to be
faulty...but the darn thing still WILL NOT work.
In the interest of clarification, I have added some information to the
schematic of the tape deck headphone amp that I'm having problems
with.
Some circuit paths are now labeled:
* i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
As always, the points at which voltage readings are marked with a star
are NOT producing the voltage indicated. The +7V location is
measuring 131mV instead. The other two points where a star is
indicated are measuring between 20mV and 30mV (fluctuating slightly).
I am starting to think that a circuit OUTSIDE of this circuit might be
at fault, because NOTHING inside of this circuit seems to be
faulty...but the darn thing still WILL NOT work.
Re: Amplifier Problem - Revised Schematic
"EADGBE" wrote ...
> In the interest of clarification, I have added some information to the
> schematic of the tape deck headphone amp that I'm having problems
> with.
>
> Some circuit paths are now labeled:
>
> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
>
> As always, the points at which voltage readings are marked with a star
> are NOT producing the voltage indicated. The +7V location is
> measuring 131mV instead. The other two points where a star is
> indicated are measuring between 20mV and 30mV (fluctuating slightly).
>
> I am starting to think that a circuit OUTSIDE of this circuit might be
> at fault, because NOTHING inside of this circuit seems to be
> faulty...but the darn thing still WILL NOT work.
Can't see what parts external to the circuit shown could
cause any of your symptoms. The input and output are
decoupled with capacitors. Furthermore, you confirm
that the internal, DC side of the input and output are
at the prescribed voltage. You have also confirmed that
the supply voltage is OK. There is nothing else externally
that could affect the circuit. I am assuming that the
node at the lower left corner finds its way back to
ground somewhere.
The question remains why the collector of Q205 is at
131mV rather than the predicted 7V. Q205 is simply
not conducting and that is causing all the rest of the
symptoms.
One of the marvelous things about stereo is that you've
got two identical channels. So you have a good one to
compare it to.
What is the base voltage of Q205 on the working side?
And what is it on your broken side?
"EADGBE" wrote ...
> In the interest of clarification, I have added some information to the
> schematic of the tape deck headphone amp that I'm having problems
> with.
>
> Some circuit paths are now labeled:
>
> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
>
> As always, the points at which voltage readings are marked with a star
> are NOT producing the voltage indicated. The +7V location is
> measuring 131mV instead. The other two points where a star is
> indicated are measuring between 20mV and 30mV (fluctuating slightly).
>
> I am starting to think that a circuit OUTSIDE of this circuit might be
> at fault, because NOTHING inside of this circuit seems to be
> faulty...but the darn thing still WILL NOT work.
Can't see what parts external to the circuit shown could
cause any of your symptoms. The input and output are
decoupled with capacitors. Furthermore, you confirm
that the internal, DC side of the input and output are
at the prescribed voltage. You have also confirmed that
the supply voltage is OK. There is nothing else externally
that could affect the circuit. I am assuming that the
node at the lower left corner finds its way back to
ground somewhere.
The question remains why the collector of Q205 is at
131mV rather than the predicted 7V. Q205 is simply
not conducting and that is causing all the rest of the
symptoms.
One of the marvelous things about stereo is that you've
got two identical channels. So you have a good one to
compare it to.
What is the base voltage of Q205 on the working side?
And what is it on your broken side?
Re: Amplifier Problem - Revised Schematic
Richard Crowley wrote:
> "EADGBE" wrote ...
>> In the interest of clarification, I have added some information to the
>> schematic of the tape deck headphone amp that I'm having problems
>> with.
>>
>> Some circuit paths are now labeled:
>>
>> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
>>
>> As always, the points at which voltage readings are marked with a star
>> are NOT producing the voltage indicated. The +7V location is
>> measuring 131mV instead. The other two points where a star is
>> indicated are measuring between 20mV and 30mV (fluctuating slightly).
>>
>> I am starting to think that a circuit OUTSIDE of this circuit might be
>> at fault, because NOTHING inside of this circuit seems to be
>> faulty...but the darn thing still WILL NOT work.
>
> Can't see what parts external to the circuit shown could
> cause any of your symptoms. The input and output are
> decoupled with capacitors. Furthermore, you confirm
> that the internal, DC side of the input and output are
> at the prescribed voltage. You have also confirmed that
> the supply voltage is OK. There is nothing else externally
> that could affect the circuit. I am assuming that the
> node at the lower left corner finds its way back to
> ground somewhere.
>
> The question remains why the collector of Q205 is at
> 131mV rather than the predicted 7V. Q205 is simply
> not conducting and that is causing all the rest of the
> symptoms.
>
> One of the marvelous things about stereo is that you've
> got two identical channels. So you have a good one to
> compare it to.
>
> What is the base voltage of Q205 on the working side?
> And what is it on your broken side?
All points to Q205 collector being open apart from one thing. On the
revised schematic, the output voltage at the junction of the two 3R3
resistors is measured as being correct. That doesn't add up at all. I
could do with seeing this voltage checked.
I've put the circuit into Pspice and played around with various fault
conditions to see what the volts do. Q205 is the only thing that seems
to reproduce the symptoms.
d
Richard Crowley wrote:
> "EADGBE" wrote ...
>> In the interest of clarification, I have added some information to the
>> schematic of the tape deck headphone amp that I'm having problems
>> with.
>>
>> Some circuit paths are now labeled:
>>
>> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
>>
>> As always, the points at which voltage readings are marked with a star
>> are NOT producing the voltage indicated. The +7V location is
>> measuring 131mV instead. The other two points where a star is
>> indicated are measuring between 20mV and 30mV (fluctuating slightly).
>>
>> I am starting to think that a circuit OUTSIDE of this circuit might be
>> at fault, because NOTHING inside of this circuit seems to be
>> faulty...but the darn thing still WILL NOT work.
>
> Can't see what parts external to the circuit shown could
> cause any of your symptoms. The input and output are
> decoupled with capacitors. Furthermore, you confirm
> that the internal, DC side of the input and output are
> at the prescribed voltage. You have also confirmed that
> the supply voltage is OK. There is nothing else externally
> that could affect the circuit. I am assuming that the
> node at the lower left corner finds its way back to
> ground somewhere.
>
> The question remains why the collector of Q205 is at
> 131mV rather than the predicted 7V. Q205 is simply
> not conducting and that is causing all the rest of the
> symptoms.
>
> One of the marvelous things about stereo is that you've
> got two identical channels. So you have a good one to
> compare it to.
>
> What is the base voltage of Q205 on the working side?
> And what is it on your broken side?
All points to Q205 collector being open apart from one thing. On the
revised schematic, the output voltage at the junction of the two 3R3
resistors is measured as being correct. That doesn't add up at all. I
could do with seeing this voltage checked.
I've put the circuit into Pspice and played around with various fault
conditions to see what the volts do. Q205 is the only thing that seems
to reproduce the symptoms.
d
Re: Amplifier Problem - Revised Schematic
EADGBE <hwbosshoss@comcast . net > wrote in news:7a5f62ce-00ec-4fac-84f3-
838743faa613@e67g2000hsa.googlegroups . com :
> In the interest of clarification, I have added some information to the
> schematic of the tape deck headphone amp that I'm having problems
> with.
>
> Some circuit paths are now labeled:
>
> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
>
> As always, the points at which voltage readings are marked with a star
> are NOT producing the voltage indicated. The +7V location is
> measuring 131mV instead. The other two points where a star is
> indicated are measuring between 20mV and 30mV (fluctuating slightly).
>
> I am starting to think that a circuit OUTSIDE of this circuit might be
> at fault, because NOTHING inside of this circuit seems to be
> faulty...but the darn thing still WILL NOT work.
You do NOT indicate the voltage on Q205's base, also Q204's collector.
If it is 11.9, then Q204 is not conducting and Q205 has no forward bias,
will not conduct, and all other bad values follow from there.
Since the OTHER voltages around Q204 are correct, the collector of Q204
should be LOWER than the 11.9 rail by half a volt or so.
It should thus be 11.4 on Q204 collector and Q205 base.
If it isn't, then Q204 is probably bad, open on the base/collector
junction.
--
bz
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+spr@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
EADGBE <hwbosshoss@comcast . net > wrote in news:7a5f62ce-00ec-4fac-84f3-
838743faa613@e67g2000hsa.googlegroups . com :
> In the interest of clarification, I have added some information to the
> schematic of the tape deck headphone amp that I'm having problems
> with.
>
> Some circuit paths are now labeled:
>
> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
>
> As always, the points at which voltage readings are marked with a star
> are NOT producing the voltage indicated. The +7V location is
> measuring 131mV instead. The other two points where a star is
> indicated are measuring between 20mV and 30mV (fluctuating slightly).
>
> I am starting to think that a circuit OUTSIDE of this circuit might be
> at fault, because NOTHING inside of this circuit seems to be
> faulty...but the darn thing still WILL NOT work.
You do NOT indicate the voltage on Q205's base, also Q204's collector.
If it is 11.9, then Q204 is not conducting and Q205 has no forward bias,
will not conduct, and all other bad values follow from there.
Since the OTHER voltages around Q204 are correct, the collector of Q204
should be LOWER than the 11.9 rail by half a volt or so.
It should thus be 11.4 on Q204 collector and Q205 base.
If it isn't, then Q204 is probably bad, open on the base/collector
junction.
--
bz
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+spr@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
Re: Amplifier Problem - Revised Schematic
bz <bz+spr@ch100-5.chem.lsu.edu> wrote in
news:Xns9A881ACC87A34WQAHBGMXSZHVspammote@130.39.198.139:
> Since the OTHER voltages around Q204 are correct, the collector of Q204
> should be LOWER than the 11.9 rail by half a volt or so.
> It should thus be 11.4 on Q204 collector and Q205 base.
>
> If it isn't, then Q204 is probably bad, open on the base/collector
> junction.
OR, the Q204 collector is not connected to to the 12 k resistor and the
base of Q205.
You said you replaced Q204. You could have a bad transistor(new parts can
be bad), a part soldered poorly, or a transistor soldered in wrong.
Check for broken traces and make sure that the orientation is correct on
Q204's replacement.
--
bz 73 de N5BZ k
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
bz <bz+spr@ch100-5.chem.lsu.edu> wrote in
news:Xns9A881ACC87A34WQAHBGMXSZHVspammote@130.39.198.139:
> Since the OTHER voltages around Q204 are correct, the collector of Q204
> should be LOWER than the 11.9 rail by half a volt or so.
> It should thus be 11.4 on Q204 collector and Q205 base.
>
> If it isn't, then Q204 is probably bad, open on the base/collector
> junction.
OR, the Q204 collector is not connected to to the 12 k resistor and the
base of Q205.
You said you replaced Q204. You could have a bad transistor(new parts can
be bad), a part soldered poorly, or a transistor soldered in wrong.
Check for broken traces and make sure that the orientation is correct on
Q204's replacement.
--
bz 73 de N5BZ k
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
Re: Amplifier Problem - Revised Schematic
"EADGBE" <hwbosshoss@comcast . net > wrote in message
news:7a5f62ce-00ec-4fac-84f3-838743faa613@e67g2000hsa.googlegroups . com ...
> In the interest of clarification, I have added some information to the
> schematic of the tape deck headphone amp that I'm having problems
> with.
>
> Some circuit paths are now labeled:
>
> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
>
> As always, the points at which voltage readings are marked with a star
> are NOT producing the voltage indicated. The +7V location is
> measuring 131mV instead. The other two points where a star is
> indicated are measuring between 20mV and 30mV (fluctuating slightly).
>
> I am starting to think that a circuit OUTSIDE of this circuit might be
> at fault, because NOTHING inside of this circuit seems to be
> faulty...but the darn thing still WILL NOT work.
Make sure your transistors are oriented the right way round, i.e. B,C & E
really are where you think they are. I remember once being stuck with a
repair where the lead out of a replacement transistor was not the same as
the original. Couldn't work out what the hell was going on for quite a
while, but C and E were reversed. (don't just use a diode check for this)
Gareth.
"EADGBE" <hwbosshoss@comcast . net > wrote in message
news:7a5f62ce-00ec-4fac-84f3-838743faa613@e67g2000hsa.googlegroups . com ...
> In the interest of clarification, I have added some information to the
> schematic of the tape deck headphone amp that I'm having problems
> with.
>
> Some circuit paths are now labeled:
>
> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
>
> As always, the points at which voltage readings are marked with a star
> are NOT producing the voltage indicated. The +7V location is
> measuring 131mV instead. The other two points where a star is
> indicated are measuring between 20mV and 30mV (fluctuating slightly).
>
> I am starting to think that a circuit OUTSIDE of this circuit might be
> at fault, because NOTHING inside of this circuit seems to be
> faulty...but the darn thing still WILL NOT work.
Make sure your transistors are oriented the right way round, i.e. B,C & E
really are where you think they are. I remember once being stuck with a
repair where the lead out of a replacement transistor was not the same as
the original. Couldn't work out what the hell was going on for quite a
while, but C and E were reversed. (don't just use a diode check for this)
Gareth.
Re: Amplifier Problem - Revised Schematic
"Gareth Magennis" <sound.service@btconnect . com > wrote in message
news:lyhPj.444$244.4@newsfe1-win.ntli . net ...
>
> "EADGBE" <hwbosshoss@comcast . net > wrote in message
> news:7a5f62ce-00ec-4fac-84f3-838743faa613@e67g2000hsa.googlegroups . com ...
>> In the interest of clarification, I have added some information to the
>> schematic of the tape deck headphone amp that I'm having problems
>> with.
>>
>> Some circuit paths are now labeled:
>>
>> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
>>
>> As always, the points at which voltage readings are marked with a star
>> are NOT producing the voltage indicated. The +7V location is
>> measuring 131mV instead. The other two points where a star is
>> indicated are measuring between 20mV and 30mV (fluctuating slightly).
>>
>> I am starting to think that a circuit OUTSIDE of this circuit might be
>> at fault, because NOTHING inside of this circuit seems to be
>> faulty...but the darn thing still WILL NOT work.
>
>
>
>
> Make sure your transistors are oriented the right way round, i.e. B,C & E
> really are where you think they are. I remember once being stuck with a
> repair where the lead out of a replacement transistor was not the same as
> the original. Couldn't work out what the hell was going on for quite a
> while, but C and E were reversed. (don't just use a diode check for this)
>
> Gareth.
>
>
As an example: BC184 and BC184L have different pinouts.
Gareth.
"Gareth Magennis" <sound.service@btconnect . com > wrote in message
news:lyhPj.444$244.4@newsfe1-win.ntli . net ...
>
> "EADGBE" <hwbosshoss@comcast . net > wrote in message
> news:7a5f62ce-00ec-4fac-84f3-838743faa613@e67g2000hsa.googlegroups . com ...
>> In the interest of clarification, I have added some information to the
>> schematic of the tape deck headphone amp that I'm having problems
>> with.
>>
>> Some circuit paths are now labeled:
>>
>> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
>>
>> As always, the points at which voltage readings are marked with a star
>> are NOT producing the voltage indicated. The +7V location is
>> measuring 131mV instead. The other two points where a star is
>> indicated are measuring between 20mV and 30mV (fluctuating slightly).
>>
>> I am starting to think that a circuit OUTSIDE of this circuit might be
>> at fault, because NOTHING inside of this circuit seems to be
>> faulty...but the darn thing still WILL NOT work.
>
>
>
>
> Make sure your transistors are oriented the right way round, i.e. B,C & E
> really are where you think they are. I remember once being stuck with a
> repair where the lead out of a replacement transistor was not the same as
> the original. Couldn't work out what the hell was going on for quite a
> while, but C and E were reversed. (don't just use a diode check for this)
>
> Gareth.
>
>
As an example: BC184 and BC184L have different pinouts.
Gareth.
Re: Amplifier Problem - Revised Schematic
Gareth Magennis wrote:
> "Gareth Magennis" wrote
> > "EADGBE" wrote
> >
> >> In the interest of clarification, I have added some information to the
> >> schematic of the tape deck headphone amp that I'm having problems
> >> with.
> >>
> >> Some circuit paths are now labeled:
> >>
> >> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
> >>
> >> As always, the points at which voltage readings are marked with a star
> >> are NOT producing the voltage indicated. The +7V location is
> >> measuring 131mV instead. The other two points where a star is
> >> indicated are measuring between 20mV and 30mV (fluctuating slightly).
> >>
> >> I am starting to think that a circuit OUTSIDE of this circuit might be
> >> at fault, because NOTHING inside of this circuit seems to be
> >> faulty...but the darn thing still WILL NOT work.
> >
> >
> > Make sure your transistors are oriented the right way round, i.e. B,C & E
> > really are where you think they are. I remember once being stuck with a
> > repair where the lead out of a replacement transistor was not the same as
> > the original. Couldn't work out what the hell was going on for quite a
> > while, but C and E were reversed. (don't just use a diode check for this)
>
>
> As an example: BC184
Centre base ('TO-18 style').
> and BC184L
Base at one end.
> have different pinouts.
>
> Gareth.
Gareth Magennis wrote:
> "Gareth Magennis" wrote
> > "EADGBE" wrote
> >
> >> In the interest of clarification, I have added some information to the
> >> schematic of the tape deck headphone amp that I'm having problems
> >> with.
> >>
> >> Some circuit paths are now labeled:
> >>
> >> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-1.jpg
> >>
> >> As always, the points at which voltage readings are marked with a star
> >> are NOT producing the voltage indicated. The +7V location is
> >> measuring 131mV instead. The other two points where a star is
> >> indicated are measuring between 20mV and 30mV (fluctuating slightly).
> >>
> >> I am starting to think that a circuit OUTSIDE of this circuit might be
> >> at fault, because NOTHING inside of this circuit seems to be
> >> faulty...but the darn thing still WILL NOT work.
> >
> >
> > Make sure your transistors are oriented the right way round, i.e. B,C & E
> > really are where you think they are. I remember once being stuck with a
> > repair where the lead out of a replacement transistor was not the same as
> > the original. Couldn't work out what the hell was going on for quite a
> > while, but C and E were reversed. (don't just use a diode check for this)
>
>
> As an example: BC184
Centre base ('TO-18 style').
> and BC184L
Base at one end.
> have different pinouts.
>
> Gareth.
Re: Amplifier Problem - Revised Schematic
I have revised the schematic further by adding the voltages at the
base of Q205 and collector of Q204....
* i240.photobucket . com /albums/ff58/eadgbe123/amplifier-2.jpg
I guess I don't have enough equipment to fix this problem. I can't
afford a 'scope right now. This will have to go on a shelf until I
can deal with it.
I have revised the schematic further by adding the voltages at the
base of Q205 and collector of Q204....
* i240.photobucket . com /albums/ff58/eadgbe123/amplifier-2.jpg
I guess I don't have enough equipment to fix this problem. I can't
afford a 'scope right now. This will have to go on a shelf until I
can deal with it.
Re: Amplifier Problem - Revised Schematic
You might want to look at pc scopes. Or ebay. If all you are doing is
audio and possibly lower rf frequencies there are lots of decent used scopes
on ebay.
"EADGBE" <hwbosshoss@comcast . net > wrote in message
news:e79927cb-9552-41f4-81e9-0c380ce099b0@f36g2000hsa.googlegroups . com ...
>
> I have revised the schematic further by adding the voltages at the
> base of Q205 and collector of Q204....
>
> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-2.jpg
>
> I guess I don't have enough equipment to fix this problem. I can't
> afford a 'scope right now. This will have to go on a shelf until I
> can deal with it.
You might want to look at pc scopes. Or ebay. If all you are doing is
audio and possibly lower rf frequencies there are lots of decent used scopes
on ebay.
"EADGBE" <hwbosshoss@comcast . net > wrote in message
news:e79927cb-9552-41f4-81e9-0c380ce099b0@f36g2000hsa.googlegroups . com ...
>
> I have revised the schematic further by adding the voltages at the
> base of Q205 and collector of Q204....
>
> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-2.jpg
>
> I guess I don't have enough equipment to fix this problem. I can't
> afford a 'scope right now. This will have to go on a shelf until I
> can deal with it.
Re: Amplifier Problem - Revised Schematic
"James" <james@nospam . com > wrote in
news:6eSdnTosdIIDSZDVnZ2dnUVZ_v-hnZ2d@earthlink . com :
> You might want to look at pc scopes. Or ebay. If all you are doing is
> audio and possibly lower rf frequencies there are lots of decent used
> scopes on ebay.
>
> "EADGBE" <hwbosshoss@comcast . net > wrote in message
> news:e79927cb-9552-41f4-81e9-0c380ce099b0@f36g2000hsa.googlegroups . com ...
>>
>> I have revised the schematic further by adding the voltages at the
>> base of Q205 and collector of Q204....
>>
>> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-2.jpg
>>
>> I guess I don't have enough equipment to fix this problem. I can't
>> afford a 'scope right now. This will have to go on a shelf until I
>> can deal with it.
You might download a program such as waveview or spectragram (demo versions
of many programs are available), make yourself a resistor divider probe and
look at the waveforms with your computer.
* w w w .waveviewdaq . com /
* w w w .neasmn.org/ben/software/gram517.zip
--
bz 73 de N5BZ k
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
"James" <james@nospam . com > wrote in
news:6eSdnTosdIIDSZDVnZ2dnUVZ_v-hnZ2d@earthlink . com :
> You might want to look at pc scopes. Or ebay. If all you are doing is
> audio and possibly lower rf frequencies there are lots of decent used
> scopes on ebay.
>
> "EADGBE" <hwbosshoss@comcast . net > wrote in message
> news:e79927cb-9552-41f4-81e9-0c380ce099b0@f36g2000hsa.googlegroups . com ...
>>
>> I have revised the schematic further by adding the voltages at the
>> base of Q205 and collector of Q204....
>>
>> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-2.jpg
>>
>> I guess I don't have enough equipment to fix this problem. I can't
>> afford a 'scope right now. This will have to go on a shelf until I
>> can deal with it.
You might download a program such as waveview or spectragram (demo versions
of many programs are available), make yourself a resistor divider probe and
look at the waveforms with your computer.
* w w w .waveviewdaq . com /
* w w w .neasmn.org/ben/software/gram517.zip
--
bz 73 de N5BZ k
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
Re: Amplifier Problem - Revised Schematic
"James" <james@nospam . com > wrote in message
news:6eSdnTosdIIDSZDVnZ2dnUVZ_v-hnZ2d@earthlink . com ...
> You might want to look at pc scopes. Or ebay. If all you are doing is
> audio and possibly lower rf frequencies there are lots of decent used
> scopes on ebay.
Last swap meet I went to I saw at least half a dozen scopes under 10 bucks.
A couple of them were even decent semi-modern looking solid state things,
probably 10-15 MHz, so this stuff does turn up.
"James" <james@nospam . com > wrote in message
news:6eSdnTosdIIDSZDVnZ2dnUVZ_v-hnZ2d@earthlink . com ...
> You might want to look at pc scopes. Or ebay. If all you are doing is
> audio and possibly lower rf frequencies there are lots of decent used
> scopes on ebay.
Last swap meet I went to I saw at least half a dozen scopes under 10 bucks.
A couple of them were even decent semi-modern looking solid state things,
probably 10-15 MHz, so this stuff does turn up.
Re: Amplifier Problem - Revised Schematic
In article <e79927cb-9552-41f4-81e9-0c380ce099b0
@f36g2000hsa.googlegroups . com >, hwbosshoss@comcast . net says...
>
> I have revised the schematic further by adding the voltages at the
> base of Q205 and collector of Q204....
>
> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-2.jpg
>
> I guess I don't have enough equipment to fix this problem. I can't
> afford a 'scope right now. This will have to go on a shelf until I
> can deal with it.
You don't need a scope for this one, just DC meter and brain power.
For the output transistors, Q207 base should be about one Volt higher
than Q208 base. If not, either Q206 is shorted or Q205 is not sourcing
current. If I can believe the voltages you show on Q205, it probably
has an open collector.
In article <e79927cb-9552-41f4-81e9-0c380ce099b0
@f36g2000hsa.googlegroups . com >, hwbosshoss@comcast . net says...
>
> I have revised the schematic further by adding the voltages at the
> base of Q205 and collector of Q204....
>
> * i240.photobucket . com /albums/ff58/eadgbe123/amplifier-2.jpg
>
> I guess I don't have enough equipment to fix this problem. I can't
> afford a 'scope right now. This will have to go on a shelf until I
> can deal with it.
You don't need a scope for this one, just DC meter and brain power.
For the output transistors, Q207 base should be about one Volt higher
than Q208 base. If not, either Q206 is shorted or Q205 is not sourcing
current. If I can believe the voltages you show on Q205, it probably
has an open collector.
Re: Amplifier Problem - Revised Schematic
What's driving me crazy is that, for the sake of learning, I replaced
Q205, Q206, and Q208, all with exact replacements that are all known
to be good, and still got exactly the same voltage readings.
What's driving me crazy is that, for the sake of learning, I replaced
Q205, Q206, and Q208, all with exact replacements that are all known
to be good, and still got exactly the same voltage readings.
