Newbie trying to repair
Hi,
I have salvaged tiny phono module from non working technics amplifier. Please see attached picture and schematic. From my newbie perspective it looks like the phono module is fed supply from approx. 0-30v transformer by making it dual (+ve 0 -ve) by adding capacitor and resistors and probably diodes ./? (see red circled parts.)
I have completely discarded rest the amplifier in junk so no longer have it. I only have tiny phono module. It's Schematic (Top corner part of schematic) says it is fed with approx +/-15v).
* earlier I had supplied it with 0-15v single supply resulting in no output. So i thought opamp might be damaged while soldering. I have replaced NJM4562 with ne5532. Will resolder original njm4562 again
My question is if I have (-15v)-(0v)-(+15v) DC where to connect center 0v from dc supply source ? I guess ground for input and output (pin number 2 and 7) are common. 3 and 6 are signal in. 1 and 8 are signal out.
Schematic
Thanks
Hi,
I have salvaged tiny phono module from non working technics amplifier. Please see attached picture and schematic. From my newbie perspective it looks like the phono module is fed supply from approx. 0-30v transformer by making it dual (+ve 0 -ve) by adding capacitor and resistors and probably diodes ./? (see red circled parts.)
I have completely discarded rest the amplifier in junk so no longer have it. I only have tiny phono module. It's Schematic (Top corner part of schematic) says it is fed with approx +/-15v).
* earlier I had supplied it with 0-15v single supply resulting in no output. So i thought opamp might be damaged while soldering. I have replaced NJM4562 with ne5532. Will resolder original njm4562 again
My question is if I have (-15v)-(0v)-(+15v) DC where to connect center 0v from dc supply source ? I guess ground for input and output (pin number 2 and 7) are common. 3 and 6 are signal in. 1 and 8 are signal out.
Schematic
Thanks
The capacitors C407...C410 are rail smoothing capacitors (they work together with R403/404) - if they are missing then you need to add them (otherwise you will probably have hum in your signal - depending on the power supply unit).
Power is +/-15V (against ground) provided to pins 4 and 5.
Ground is provided to pins 2 and 7.
D405/406 are zeners converting (with their resistor set) 35V to 15V.
OK. New Power supply will have filter capacitors. But if I have 15-0-15v DC will connecting 0v point to any ground work ? (any one 2 or 7 pin number ?)
thanks
thanks
Not decided. Will probably be separate phono pre.
As i dont like throwing out working things. Atleast i get to hear how it sounds and learn few things.
Regds.
As i dont like throwing out working things. Atleast i get to hear how it sounds and learn few things.
Regds.
Cost of laziness :
In hastiness didn't bothered to test with series bulb tester. Some wires shorted at bottom connector. Original Opamp njm4562 smoked and died. Getting no sound.
Replaced with 40US cents fake NE5532. touched the input with fingers. There was humming buzz on both channels, so connected TT<>Phonopreamplifier<>Computer Speakers. Lots of hissing noise. Replaced 33uf C3 capacitor as it measured 15uf on multimeter. No change. My power supply is from CNC Phono stage with DC output set at 15-0-15v. 0V wire connected to pin number 7 of phono board. So I guess that is ok./?
However when I switch off the power supply at the end the music sound comes loud and clean(as if everything is fine). Hear attached file at lower mid volume. What coud be the cause ? Any parts to replace ?
my power supply
Audio test file : at 0.8 time I switch off the power supply to phono preamplifier. At 0.18 the music is cleanest as if everything is working perfectly. (link will work for 24 hrs., If play button does not work, refresh the webpage)
https://jmp.sh/s/d20OkG2YXiXDq4U2M7TI
Help appreciated.
Thanks
In hastiness didn't bothered to test with series bulb tester. Some wires shorted at bottom connector. Original Opamp njm4562 smoked and died. Getting no sound.
Replaced with 40US cents fake NE5532. touched the input with fingers. There was humming buzz on both channels, so connected TT<>Phonopreamplifier<>Computer Speakers. Lots of hissing noise. Replaced 33uf C3 capacitor as it measured 15uf on multimeter. No change. My power supply is from CNC Phono stage with DC output set at 15-0-15v. 0V wire connected to pin number 7 of phono board. So I guess that is ok./?
However when I switch off the power supply at the end the music sound comes loud and clean(as if everything is fine). Hear attached file at lower mid volume. What coud be the cause ? Any parts to replace ?
my power supply
Audio test file : at 0.8 time I switch off the power supply to phono preamplifier. At 0.18 the music is cleanest as if everything is working perfectly. (link will work for 24 hrs., If play button does not work, refresh the webpage)
https://jmp.sh/s/d20OkG2YXiXDq4U2M7TI
Help appreciated.
Thanks
Looks like the board has many parts missing, i see not a single resistor there. Probably you should rebuild the circuit following the schema.
Then you should check every component or replace everything (it'll cost nothing except your time) because your power supply looks good to me.
madis64, it is music from turntable to phono preamp mentioned and from phono preamp out to computer speakers. Do listen to music sample attached. it is interesting as why when power is switched off the hiss disappears after some time and clean music plays.
Try conventional integrated amplifier and headphones - nobody knows you computer speakers.