Mixing
Does anyone know what this does?
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My grandmother asked me if i could fix her old portable record player, so i took a look at it and the motor wouldnt spin, so i opened it up and found a schematic inside, nothing seems bad or broken in the machine, but when i measure the voltage between the motor + and - its only getting .3 volts dc while it should be between 9 and 12 volts, upon further testing i noticed that when wiring the motor - directly to ground it works fine, yet in the schematic it goes through a little part of the circuit with two npn transistors, does anyone know why that part is there or what it does? Why not just wire it directle to ground?
Thanks in advance
Edit1 btw I already took out and tested both transistors on a multimeter, nothing odd to them
Edit 2 as sugested by jasen i checked voltage on R571, and its 11.09 volts on one side of it and, near to nothing on the other side, its also a really wierd resistor ( picture added)
transistors dc-motor
asked 2 hours ago
Nook
256
 |Â
show 9 more comments
up vote
1
down vote
favorite
My grandmother asked me if i could fix her old portable record player, so i took a look at it and the motor wouldnt spin, so i opened it up and found a schematic inside, nothing seems bad or broken in the machine, but when i measure the voltage between the motor + and - its only getting .3 volts dc while it should be between 9 and 12 volts, upon further testing i noticed that when wiring the motor - directly to ground it works fine, yet in the schematic it goes through a little part of the circuit with two npn transistors, does anyone know why that part is there or what it does? Why not just wire it directle to ground?
Thanks in advance
Edit1 btw I already took out and tested both transistors on a multimeter, nothing odd to them
Edit 2 as sugested by jasen i checked voltage on R571, and its 11.09 volts on one side of it and, near to nothing on the other side, its also a really wierd resistor ( picture added)
transistors dc-motor
asked 2 hours ago
Nook
256
1
The two transistors are there to control the motor speed. Most likely something wrong in that area if the motor doesn't turn.
– JRE
2 hours ago
1
I fixed your image. Please pay attention to up and down in the future.
– JRE
2 hours ago
1
check that the contacts 491/492 are clean and pass electricity. you may need to move the tone needle end of the tone arm towards the centre of the platter to close the contacts. transformer will be +/- 5% on voltage same as mains
– Jasen
1 hour ago
1
ha! check R571 if that's good measure voltage from ground/negative on pins of TS451 and TS452 when the motor should be running
– Jasen
1 hour ago
1
If you bypass the speed regulator, records will sound awful. Everything will play too fast, especially when using AC power, and the speed will vary with the battery voltage. That circuit is in there for a reason, and you need to figure out what's wrong with it. You've got 9V across the circuit as a whole, but only a small voltage across the motor itself. The rest of the voltage has to appear somewhere (across either TS452 or R571) -- so find out which component it is, and then you can figure out why.
– Dave Tweed♦
1 hour ago
 |Â
show 9 more comments
up vote
1
down vote
favorite
up vote
1
down vote
favorite
My grandmother asked me if i could fix her old portable record player, so i took a look at it and the motor wouldnt spin, so i opened it up and found a schematic inside, nothing seems bad or broken in the machine, but when i measure the voltage between the motor + and - its only getting .3 volts dc while it should be between 9 and 12 volts, upon further testing i noticed that when wiring the motor - directly to ground it works fine, yet in the schematic it goes through a little part of the circuit with two npn transistors, does anyone know why that part is there or what it does? Why not just wire it directle to ground?
Thanks in advance
Edit1 btw I already took out and tested both transistors on a multimeter, nothing odd to them
Edit 2 as sugested by jasen i checked voltage on R571, and its 11.09 volts on one side of it and, near to nothing on the other side, its also a really wierd resistor ( picture added)
transistors dc-motor
asked 2 hours ago
Nook
256
My grandmother asked me if i could fix her old portable record player, so i took a look at it and the motor wouldnt spin, so i opened it up and found a schematic inside, nothing seems bad or broken in the machine, but when i measure the voltage between the motor + and - its only getting .3 volts dc while it should be between 9 and 12 volts, upon further testing i noticed that when wiring the motor - directly to ground it works fine, yet in the schematic it goes through a little part of the circuit with two npn transistors, does anyone know why that part is there or what it does? Why not just wire it directle to ground?
Thanks in advance
Edit1 btw I already took out and tested both transistors on a multimeter, nothing odd to them
Edit 2 as sugested by jasen i checked voltage on R571, and its 11.09 volts on one side of it and, near to nothing on the other side, its also a really wierd resistor ( picture added)
transistors dc-motor
transistors dc-motor
asked 2 hours ago
Nook
256
asked 2 hours ago
Nook
256
edited 1 hour ago
asked 2 hours ago
Nook
256
asked 2 hours ago
Nook
256
asked 2 hours ago
Nook
256
256
1
The two transistors are there to control the motor speed. Most likely something wrong in that area if the motor doesn't turn.
– JRE
2 hours ago
1
I fixed your image. Please pay attention to up and down in the future.
– JRE
2 hours ago
1
check that the contacts 491/492 are clean and pass electricity. you may need to move the tone needle end of the tone arm towards the centre of the platter to close the contacts. transformer will be +/- 5% on voltage same as mains
– Jasen
1 hour ago
1
ha! check R571 if that's good measure voltage from ground/negative on pins of TS451 and TS452 when the motor should be running
– Jasen
1 hour ago
1
If you bypass the speed regulator, records will sound awful. Everything will play too fast, especially when using AC power, and the speed will vary with the battery voltage. That circuit is in there for a reason, and you need to figure out what's wrong with it. You've got 9V across the circuit as a whole, but only a small voltage across the motor itself. The rest of the voltage has to appear somewhere (across either TS452 or R571) -- so find out which component it is, and then you can figure out why.
– Dave Tweed♦
1 hour ago
 |Â
show 9 more comments
1
The two transistors are there to control the motor speed. Most likely something wrong in that area if the motor doesn't turn.
– JRE
2 hours ago
1
I fixed your image. Please pay attention to up and down in the future.
– JRE
2 hours ago
1
check that the contacts 491/492 are clean and pass electricity. you may need to move the tone needle end of the tone arm towards the centre of the platter to close the contacts. transformer will be +/- 5% on voltage same as mains
– Jasen
1 hour ago
1
ha! check R571 if that's good measure voltage from ground/negative on pins of TS451 and TS452 when the motor should be running
– Jasen
1 hour ago
1
If you bypass the speed regulator, records will sound awful. Everything will play too fast, especially when using AC power, and the speed will vary with the battery voltage. That circuit is in there for a reason, and you need to figure out what's wrong with it. You've got 9V across the circuit as a whole, but only a small voltage across the motor itself. The rest of the voltage has to appear somewhere (across either TS452 or R571) -- so find out which component it is, and then you can figure out why.
– Dave Tweed♦
1 hour ago
1
1
The two transistors are there to control the motor speed. Most likely something wrong in that area if the motor doesn't turn.
– JRE
2 hours ago
The two transistors are there to control the motor speed. Most likely something wrong in that area if the motor doesn't turn.
– JRE
2 hours ago
1
1
I fixed your image. Please pay attention to up and down in the future.
– JRE
2 hours ago
I fixed your image. Please pay attention to up and down in the future.
– JRE
2 hours ago
1
1
check that the contacts 491/492 are clean and pass electricity. you may need to move the tone needle end of the tone arm towards the centre of the platter to close the contacts. transformer will be +/- 5% on voltage same as mains
– Jasen
1 hour ago
check that the contacts 491/492 are clean and pass electricity. you may need to move the tone needle end of the tone arm towards the centre of the platter to close the contacts. transformer will be +/- 5% on voltage same as mains
– Jasen
1 hour ago
1
1
ha! check R571 if that's good measure voltage from ground/negative on pins of TS451 and TS452 when the motor should be running
– Jasen
1 hour ago
ha! check R571 if that's good measure voltage from ground/negative on pins of TS451 and TS452 when the motor should be running
– Jasen
1 hour ago
1
1
If you bypass the speed regulator, records will sound awful. Everything will play too fast, especially when using AC power, and the speed will vary with the battery voltage. That circuit is in there for a reason, and you need to figure out what's wrong with it. You've got 9V across the circuit as a whole, but only a small voltage across the motor itself. The rest of the voltage has to appear somewhere (across either TS452 or R571) -- so find out which component it is, and then you can figure out why.
– Dave Tweed♦
1 hour ago
If you bypass the speed regulator, records will sound awful. Everything will play too fast, especially when using AC power, and the speed will vary with the battery voltage. That circuit is in there for a reason, and you need to figure out what's wrong with it. You've got 9V across the circuit as a whole, but only a small voltage across the motor itself. The rest of the voltage has to appear somewhere (across either TS452 or R571) -- so find out which component it is, and then you can figure out why.
– Dave Tweed♦
1 hour ago
 |Â
show 9 more comments
2 Answers
2
active
oldest
votes
up vote
3
down vote
accepted
to get constant speed from a PMDC brushed motor, you regulate the back-emf.
to measure this you need to subtract the voltage drop in the motor's internal resistance from the voltage seen on the motor terminals, you can get that voltage by ohm's law if you know the current through the motor.
R571 measure the motor current. the chain R566-R567-R568 measure the voltage across the motor-r571 combination and TS451 compares some fraction of the total voltage against R571 + V_be when the motor voltage is too high TS451 conducts more, this reduces the current available for TS452 base, which reduces the current it passes.
answered 55 mins ago
Jasen
8,3611326
An Emitter follower is not a current sense regulator, but the collector drop is a current limiter for TS452 for over current protection (OCP) in case of a motor short. ALL Emitter FOllowers must have an emitter resistance smaller than the load ( Rcoil < <R Motor) The coil R571 pulls down the motor for >nominal speed, lower=faster. The Pot pulls the emitter up to reduce the Motor voltage for a calibratedEMF is a rating of kV/RPM if there was no friction and with slight friction this motor voltage is slightly more to produce the exact voltage to drive at the right RPM e.g. 33 1/3 RPM.
– Tony EE rocketscientist
28 mins ago
So a solder joint was the fault, but the explanation of Theory of Operation was incorrect. No matter. it was fixed and led to a solution
– Tony EE rocketscientist
26 mins ago
add a comment |Â
up vote
0
down vote
Thanks to everybody who helped in the comments, its fixed i believe, other than r571 being 6.7ohm instead of 4.8ohm, everything works now, so thanks a lot guys!
answered 52 mins ago
Nook
256
Vote for and accept the given answers. This isn't a forum.
– JRE
49 mins ago
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
3
down vote
accepted
to get constant speed from a PMDC brushed motor, you regulate the back-emf.
to measure this you need to subtract the voltage drop in the motor's internal resistance from the voltage seen on the motor terminals, you can get that voltage by ohm's law if you know the current through the motor.
R571 measure the motor current. the chain R566-R567-R568 measure the voltage across the motor-r571 combination and TS451 compares some fraction of the total voltage against R571 + V_be when the motor voltage is too high TS451 conducts more, this reduces the current available for TS452 base, which reduces the current it passes.
answered 55 mins ago
Jasen
8,3611326
An Emitter follower is not a current sense regulator, but the collector drop is a current limiter for TS452 for over current protection (OCP) in case of a motor short. ALL Emitter FOllowers must have an emitter resistance smaller than the load ( Rcoil < <R Motor) The coil R571 pulls down the motor for >nominal speed, lower=faster. The Pot pulls the emitter up to reduce the Motor voltage for a calibratedEMF is a rating of kV/RPM if there was no friction and with slight friction this motor voltage is slightly more to produce the exact voltage to drive at the right RPM e.g. 33 1/3 RPM.
– Tony EE rocketscientist
28 mins ago
So a solder joint was the fault, but the explanation of Theory of Operation was incorrect. No matter. it was fixed and led to a solution
– Tony EE rocketscientist
26 mins ago
add a comment |Â
up vote
3
down vote
accepted
to get constant speed from a PMDC brushed motor, you regulate the back-emf.
to measure this you need to subtract the voltage drop in the motor's internal resistance from the voltage seen on the motor terminals, you can get that voltage by ohm's law if you know the current through the motor.
R571 measure the motor current. the chain R566-R567-R568 measure the voltage across the motor-r571 combination and TS451 compares some fraction of the total voltage against R571 + V_be when the motor voltage is too high TS451 conducts more, this reduces the current available for TS452 base, which reduces the current it passes.
answered 55 mins ago
Jasen
8,3611326
An Emitter follower is not a current sense regulator, but the collector drop is a current limiter for TS452 for over current protection (OCP) in case of a motor short. ALL Emitter FOllowers must have an emitter resistance smaller than the load ( Rcoil < <R Motor) The coil R571 pulls down the motor for >nominal speed, lower=faster. The Pot pulls the emitter up to reduce the Motor voltage for a calibratedEMF is a rating of kV/RPM if there was no friction and with slight friction this motor voltage is slightly more to produce the exact voltage to drive at the right RPM e.g. 33 1/3 RPM.
– Tony EE rocketscientist
28 mins ago
So a solder joint was the fault, but the explanation of Theory of Operation was incorrect. No matter. it was fixed and led to a solution
– Tony EE rocketscientist
26 mins ago
add a comment |Â
up vote
3
down vote
accepted
up vote
3
down vote
accepted
to get constant speed from a PMDC brushed motor, you regulate the back-emf.
to measure this you need to subtract the voltage drop in the motor's internal resistance from the voltage seen on the motor terminals, you can get that voltage by ohm's law if you know the current through the motor.
R571 measure the motor current. the chain R566-R567-R568 measure the voltage across the motor-r571 combination and TS451 compares some fraction of the total voltage against R571 + V_be when the motor voltage is too high TS451 conducts more, this reduces the current available for TS452 base, which reduces the current it passes.
answered 55 mins ago
Jasen
8,3611326
to get constant speed from a PMDC brushed motor, you regulate the back-emf.
to measure this you need to subtract the voltage drop in the motor's internal resistance from the voltage seen on the motor terminals, you can get that voltage by ohm's law if you know the current through the motor.
R571 measure the motor current. the chain R566-R567-R568 measure the voltage across the motor-r571 combination and TS451 compares some fraction of the total voltage against R571 + V_be when the motor voltage is too high TS451 conducts more, this reduces the current available for TS452 base, which reduces the current it passes.
answered 55 mins ago
Jasen
8,3611326
answered 55 mins ago
Jasen
8,3611326
answered 55 mins ago
Jasen
8,3611326
answered 55 mins ago
Jasen
8,3611326
8,3611326
An Emitter follower is not a current sense regulator, but the collector drop is a current limiter for TS452 for over current protection (OCP) in case of a motor short. ALL Emitter FOllowers must have an emitter resistance smaller than the load ( Rcoil < <R Motor) The coil R571 pulls down the motor for >nominal speed, lower=faster. The Pot pulls the emitter up to reduce the Motor voltage for a calibratedEMF is a rating of kV/RPM if there was no friction and with slight friction this motor voltage is slightly more to produce the exact voltage to drive at the right RPM e.g. 33 1/3 RPM.
– Tony EE rocketscientist
28 mins ago
So a solder joint was the fault, but the explanation of Theory of Operation was incorrect. No matter. it was fixed and led to a solution
– Tony EE rocketscientist
26 mins ago
add a comment |Â
An Emitter follower is not a current sense regulator, but the collector drop is a current limiter for TS452 for over current protection (OCP) in case of a motor short. ALL Emitter FOllowers must have an emitter resistance smaller than the load ( Rcoil < <R Motor) The coil R571 pulls down the motor for >nominal speed, lower=faster. The Pot pulls the emitter up to reduce the Motor voltage for a calibratedEMF is a rating of kV/RPM if there was no friction and with slight friction this motor voltage is slightly more to produce the exact voltage to drive at the right RPM e.g. 33 1/3 RPM.
– Tony EE rocketscientist
28 mins ago
So a solder joint was the fault, but the explanation of Theory of Operation was incorrect. No matter. it was fixed and led to a solution
– Tony EE rocketscientist
26 mins ago
An Emitter follower is not a current sense regulator, but the collector drop is a current limiter for TS452 for over current protection (OCP) in case of a motor short. ALL Emitter FOllowers must have an emitter resistance smaller than the load ( Rcoil < <R Motor) The coil R571 pulls down the motor for >nominal speed, lower=faster. The Pot pulls the emitter up to reduce the Motor voltage for a calibratedEMF is a rating of kV/RPM if there was no friction and with slight friction this motor voltage is slightly more to produce the exact voltage to drive at the right RPM e.g. 33 1/3 RPM.
– Tony EE rocketscientist
28 mins ago
An Emitter follower is not a current sense regulator, but the collector drop is a current limiter for TS452 for over current protection (OCP) in case of a motor short. ALL Emitter FOllowers must have an emitter resistance smaller than the load ( Rcoil < <R Motor) The coil R571 pulls down the motor for >nominal speed, lower=faster. The Pot pulls the emitter up to reduce the Motor voltage for a calibratedEMF is a rating of kV/RPM if there was no friction and with slight friction this motor voltage is slightly more to produce the exact voltage to drive at the right RPM e.g. 33 1/3 RPM.
– Tony EE rocketscientist
28 mins ago
So a solder joint was the fault, but the explanation of Theory of Operation was incorrect. No matter. it was fixed and led to a solution
– Tony EE rocketscientist
26 mins ago
So a solder joint was the fault, but the explanation of Theory of Operation was incorrect. No matter. it was fixed and led to a solution
– Tony EE rocketscientist
26 mins ago
add a comment |Â
up vote
0
down vote
Thanks to everybody who helped in the comments, its fixed i believe, other than r571 being 6.7ohm instead of 4.8ohm, everything works now, so thanks a lot guys!
answered 52 mins ago
Nook
256
Vote for and accept the given answers. This isn't a forum.
– JRE
49 mins ago
add a comment |Â
up vote
0
down vote
Thanks to everybody who helped in the comments, its fixed i believe, other than r571 being 6.7ohm instead of 4.8ohm, everything works now, so thanks a lot guys!
answered 52 mins ago
Nook
256
Vote for and accept the given answers. This isn't a forum.
– JRE
49 mins ago
add a comment |Â
up vote
0
down vote
up vote
0
down vote
Thanks to everybody who helped in the comments, its fixed i believe, other than r571 being 6.7ohm instead of 4.8ohm, everything works now, so thanks a lot guys!
answered 52 mins ago
Nook
256
Thanks to everybody who helped in the comments, its fixed i believe, other than r571 being 6.7ohm instead of 4.8ohm, everything works now, so thanks a lot guys!
answered 52 mins ago
Nook
256
answered 52 mins ago
Nook
256
answered 52 mins ago
Nook
256
answered 52 mins ago
Nook
256
256
Vote for and accept the given answers. This isn't a forum.
– JRE
49 mins ago
add a comment |Â
Vote for and accept the given answers. This isn't a forum.
– JRE
49 mins ago
Vote for and accept the given answers. This isn't a forum.
– JRE
49 mins ago
Vote for and accept the given answers. This isn't a forum.
– JRE
49 mins ago
add a comment |Â
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1
The two transistors are there to control the motor speed. Most likely something wrong in that area if the motor doesn't turn.
– JRE
2 hours ago
1
I fixed your image. Please pay attention to up and down in the future.
– JRE
2 hours ago
1
check that the contacts 491/492 are clean and pass electricity. you may need to move the tone needle end of the tone arm towards the centre of the platter to close the contacts. transformer will be +/- 5% on voltage same as mains
– Jasen
1 hour ago
1
ha! check R571 if that's good measure voltage from ground/negative on pins of TS451 and TS452 when the motor should be running
– Jasen
1 hour ago
1
If you bypass the speed regulator, records will sound awful. Everything will play too fast, especially when using AC power, and the speed will vary with the battery voltage. That circuit is in there for a reason, and you need to figure out what's wrong with it. You've got 9V across the circuit as a whole, but only a small voltage across the motor itself. The rest of the voltage has to appear somewhere (across either TS452 or R571) -- so find out which component it is, and then you can figure out why.
– Dave Tweed♦
1 hour ago