Hi guys. Again I need advice.
This is NAD integrated amp.
At the output of regulator IC901 M5231L - pin2 there is 0V
I desolder and tested, it is defective
My question is can I replace it with another regulator or zener diode (the emitter of Q901 should be obtained +46V)
M5231L
Cheers!
This is NAD integrated amp.
At the output of regulator IC901 M5231L - pin2 there is 0V
I desolder and tested, it is defective
My question is can I replace it with another regulator or zener diode (the emitter of Q901 should be obtained +46V)
M5231L
Cheers!
Attachments
First thought would be to replace the reg and transistor with a 3 terminal high voltage adjustable reg. The LM317AHV has a 60 volt rating (voltage across the device) and the TL783 is 125 volt rating. Just calculate the resistors needed from the data sheet to give +46 volts.
Attachments
Thanks for the reply.
And what do you think of the use of 47V zener diode to base Q901?
Will it be appropriate?
And what do you think of the use of 47V zener diode to base Q901?
Will it be appropriate?
A Zener and suitable resistor feeding it would probably work but would be inferior in absolute stability over a regulator.
You would need to look at the current requirements of that rail and see if the Zener was workable. The gain of the transistor comes into play here. A 47 volt Zener of lets say 1 watt rating can only pass around 20 milliamps. That means only around say 10 to 15 ma is available for the base current (if you design for such things as what happens if the load is low) and that may or may not be enough.
(I see the reservoir caps are 470uF and so that does suggest a low current supply)
You would need to look at the current requirements of that rail and see if the Zener was workable. The gain of the transistor comes into play here. A 47 volt Zener of lets say 1 watt rating can only pass around 20 milliamps. That means only around say 10 to 15 ma is available for the base current (if you design for such things as what happens if the load is low) and that may or may not be enough.
(I see the reservoir caps are 470uF and so that does suggest a low current supply)
I found a complete datasheet for the M5231L in a databook.
Replacing this part adequately may prove a bit more difficult than one might think... while a different value of Vref would easily be accommodated by changing some resistors (this part has its 1.8 V Vref on the ground side, unlike LM317HV or TL783), the M5231L also is a low-noise high-voltage regulator (Vno = 6 µV typ @ 20 Hz - 100 kHz, max 70 V in, max 50 V out).
When substituting an LM317HV (make sure thermals are taken care of!), this would be calling for an ADJ pin capacitor and both protection diodes... and even then output noise would still be substantially higher if the LM317HV spec of Vno = 0.003% * Vout (10 Hz - 10 kHz) is accurate... that would be ~37.5 µV.
What are the requrements in terms of noise and how much current is required? Since the original circuit is lacking suggested capacitor Cref (the counterpart of the ADJ pin capacitor), it's not that low-noise either... about 157 µV @ 100 kHz BW. And it looks like we are feeding power amp input + protection... so probably dozens of mA, not anything super severe. If all fails, it may still be possible to upgrade the 10 ohm dropper resistors to take some thermal dissipation off the reg.
Have you measured beta on the 2SD414 pass transistor? If that's cooked, it may have overloaded the M5231L.
I would suggest having this thread moved to Power Supplies, seems like a better fit over there.
Replacing this part adequately may prove a bit more difficult than one might think... while a different value of Vref would easily be accommodated by changing some resistors (this part has its 1.8 V Vref on the ground side, unlike LM317HV or TL783), the M5231L also is a low-noise high-voltage regulator (Vno = 6 µV typ @ 20 Hz - 100 kHz, max 70 V in, max 50 V out).
When substituting an LM317HV (make sure thermals are taken care of!), this would be calling for an ADJ pin capacitor and both protection diodes... and even then output noise would still be substantially higher if the LM317HV spec of Vno = 0.003% * Vout (10 Hz - 10 kHz) is accurate... that would be ~37.5 µV.
What are the requrements in terms of noise and how much current is required? Since the original circuit is lacking suggested capacitor Cref (the counterpart of the ADJ pin capacitor), it's not that low-noise either... about 157 µV @ 100 kHz BW. And it looks like we are feeding power amp input + protection... so probably dozens of mA, not anything super severe. If all fails, it may still be possible to upgrade the 10 ohm dropper resistors to take some thermal dissipation off the reg.
Have you measured beta on the 2SD414 pass transistor? If that's cooked, it may have overloaded the M5231L.
I would suggest having this thread moved to Power Supplies, seems like a better fit over there.
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