Good morning,
Still looking for working transistor D287B. Now here stuck up. There are old shops in market. They said if not the same they will manage equivalent transistor from old amplifier. Let's hope.
Can anyone tell if I remove this transistor from circuit because it is parallel with another 2SD287B. Will amplifier work or not. Will it give DC voltages to speaker terminals.
Thanks.
Still looking for working transistor D287B. Now here stuck up. There are old shops in market. They said if not the same they will manage equivalent transistor from old amplifier. Let's hope.
Can anyone tell if I remove this transistor from circuit because it is parallel with another 2SD287B. Will amplifier work or not. Will it give DC voltages to speaker terminals.
Thanks.
It is difficult for me to explain something in an understandable way and English is not my native language.
First question: Are the capacitors on power supply module P647 now been replaced?
Second question: in the middle of board P647 I see a setting pot (blue), what is that? because I have never come across this modification before.
I understand from your post that you manually trigger the power supply with a resistor of 4.7K and that the power supply then turns on and that the output voltages are then 51 Volts. And are these voltages adjustable with VR901 and VR902? But this triggering must be done again and again when the device has been switched off.
In the service Manuel you can see that these voltages of 51 Volts are too low in my opinion, and that these voltages should be at least 55 Volts, see fig 6.2.
You can also see that a current of 3mA must flow through the zeners.
The resistor that should regulate this has a value of 2200 Ohm.
A simple calculation Ohms law U=IXR 2200X0.003=6.6 Volt rounded to 7 Volt because the base current of Q903 is also added.
So a voltage of approximately 7 Volts falls across resistor 917. Add the zener voltage of 48 Volts and you arrive at 55 Volts.
In my view, the -4 Volt offset on both speaker outputs L/R indicates that there is a common problem and then I end up with power board P647.
The amplifier should also be able to work with one power output board.
You should also read this topic on Audiokarma. Luxman L-100U Power Supply Issues?
First question: Are the capacitors on power supply module P647 now been replaced?
Second question: in the middle of board P647 I see a setting pot (blue), what is that? because I have never come across this modification before.
I understand from your post that you manually trigger the power supply with a resistor of 4.7K and that the power supply then turns on and that the output voltages are then 51 Volts. And are these voltages adjustable with VR901 and VR902? But this triggering must be done again and again when the device has been switched off.
In the service Manuel you can see that these voltages of 51 Volts are too low in my opinion, and that these voltages should be at least 55 Volts, see fig 6.2.
You can also see that a current of 3mA must flow through the zeners.
The resistor that should regulate this has a value of 2200 Ohm.
A simple calculation Ohms law U=IXR 2200X0.003=6.6 Volt rounded to 7 Volt because the base current of Q903 is also added.
So a voltage of approximately 7 Volts falls across resistor 917. Add the zener voltage of 48 Volts and you arrive at 55 Volts.
In my view, the -4 Volt offset on both speaker outputs L/R indicates that there is a common problem and then I end up with power board P647.
The amplifier should also be able to work with one power output board.
You should also read this topic on Audiokarma. Luxman L-100U Power Supply Issues?
Non of the capacitor changed on P647 PS board. I removed few capacitor from board and then read the values and found different what is printed on the capacitor. What I understand that I should change the capacitors.
In the middle of board there is trim pot. I did not rotate it. I thought it is original.
Yes, I manually started the power supply unit through 4.7 k jumper.
I did not turn the VR901 & VR902 because I was very happy and don't want to change voltage. What I understand that I should trim it if possible to bring the voltage levels to + - 58.
This is the answer for which I was waiting for, you said single channel will work and must give sound. I removed the inputs of PB649 @ connector C09M >C10M that is I think coming from pre stage to verify that there is no DC bias voltage coming from pre stage to drive stage.
Your English is better than me. Yes. My friend who made copy of Musical Fidelity A1, He used complementary pair of transistors MJ series he suggested that I can get from him a pair of MJ802 PNP (TO3) package as a replacement for testing only, until I get 2SD287B. Power stage transistor. What you suggest.
Touch mute is also not working. I think Mute means no sound from amplifier or attenuate the sound once touch. Please guide if possible for you.
Now again your expert opinion required about board P649.
Referring to connector C11M>>>>C18M. Power supply (C18M,17MRed +55 volts then C16MBlue {seems output} then C15MBlack {0 reference volts} then C14,13MGrey {-55 volts}, then C12,11M {48Volts}
As per your guidance voltage should be 48 volts because of two zener diodes on both sides but here volts are 54 on C12,11M these should be 48. Let me calibrate from three trim pots on P647, may be it works. If not then it may be due to damaged zener diodes 24 volts which are in series. Let me find and reply here.
Extremely thanks for your guidance.
Referring to connector C11M>>>>C18M. Power supply (C18M,17MRed +55 volts then C16MBlue {seems output} then C15MBlack {0 reference volts} then C14,13MGrey {-55 volts}, then C12,11M {48Volts}
As per your guidance voltage should be 48 volts because of two zener diodes on both sides but here volts are 54 on C12,11M these should be 48. Let me calibrate from three trim pots on P647, may be it works. If not then it may be due to damaged zener diodes 24 volts which are in series. Let me find and reply here.
Extremely thanks for your guidance.
Trimming pot 901 is working and three volts up/down (54~ 51) on CO7S>>>C20S but trimming pot 902 is not making any difference on the voltage on CO7S>>>C20S
This means some problem in power supply.
Regarding left/right channel if I remove any of the pin left side blue, right side white out from connector(C11M>>>>C18M) then amp does not need to get ON with the help of jumper 4.7 k. It gets ON normally.
I think it is due to 54 volts on C07S>>>C10S. Once these volts got controlled to 48 instead of 54 volts amplifier will comes to running stage.
Please comment. 😇
This means some problem in power supply.
Regarding left/right channel if I remove any of the pin left side blue, right side white out from connector(C11M>>>>C18M) then amp does not need to get ON with the help of jumper 4.7 k. It gets ON normally.
I think it is due to 54 volts on C07S>>>C10S. Once these volts got controlled to 48 instead of 54 volts amplifier will comes to running stage.
Please comment. 😇
In this case, measuring is knowing
So you have to find out why VR901 works and VR902 doesn't.
The positive and negative power supply are basically the same, only the transistors are different NPN/PNP.
So you have to measure where the differences are between the positive and the
negative power supply and again this problem can also be caused by bad capacitors.
I would start at the front by measuring the voltages with ground as reference and start with Q901/Q902, especially what are the emitter voltages and what currents flow through them and so on. And also measure the alternating voltages on the bridge cell. And what is the ripple voltage after rectification?
And the measured maximum positive voltage of 54 Volt also remains on the low side. Forget that 48 Volt because that is a reference voltage for the power supply itself and is not the output voltages.
The 48 Volt is made with two 24 Volt zeners in series,
one is used in combination with an emitter follower (Q507/508) for the 24 Volt voltages that feed the pre amp.
The input connector on board P649 must be connected because the ground is important for P649.
There is a switch on the back of the device that can be used to disable the touch mute function.
The MJ21193/94 is probably a better replacement ON Semiconductors..
Make sure you buy these parts from a reliable source Mouser DigiKey, otherwise you run the risk of getting fake parts.
Have you also read the Audiokarma topic? because there is more information about what the output voltage P647 should be.
I'm retired now and it's been a while since I worked on an L100.
So you have to find out why VR901 works and VR902 doesn't.
The positive and negative power supply are basically the same, only the transistors are different NPN/PNP.
So you have to measure where the differences are between the positive and the
negative power supply and again this problem can also be caused by bad capacitors.
I would start at the front by measuring the voltages with ground as reference and start with Q901/Q902, especially what are the emitter voltages and what currents flow through them and so on. And also measure the alternating voltages on the bridge cell. And what is the ripple voltage after rectification?
And the measured maximum positive voltage of 54 Volt also remains on the low side. Forget that 48 Volt because that is a reference voltage for the power supply itself and is not the output voltages.
The 48 Volt is made with two 24 Volt zeners in series,
one is used in combination with an emitter follower (Q507/508) for the 24 Volt voltages that feed the pre amp.
The input connector on board P649 must be connected because the ground is important for P649.
There is a switch on the back of the device that can be used to disable the touch mute function.
The MJ21193/94 is probably a better replacement ON Semiconductors..
Make sure you buy these parts from a reliable source Mouser DigiKey, otherwise you run the risk of getting fake parts.
Have you also read the Audiokarma topic? because there is more information about what the output voltage P647 should be.
I'm retired now and it's been a while since I worked on an L100.
