I must not have done it correctly. I’ll try again on 20V. Red lead on a resistor and black on a ground.
Barn find Sansui AU-7900
- Thread starter Kylek1443
- Start date
Ok redoing it hopefully correctly this time. MM on 20V, power on, black lead in negative speaker terminal, red lead on resistor. I got 7.49v on R-30 and 6.64V on R-29
Ahhh. Volume was at zero and source was on AUX but I was not on DC. I need to swap my red lead over to 10ADC. Let me try it again! Lol. Hopefully 3rd time is a charm
Doing it with the red lead swapped over to 10ADC doesn’t move the MM at all. It does dim the bulb and make it flash for a second though.
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GrisPato
Super Member
Sorry for confusing you. The leads.of the DMM were in the right place. Just wanted to make sure you had range on DC volt and not AC.
I can not make anything with the readings you got. From that resistor you will have three diode voltage drops (be) which would mean you would have around 5 volt left for the quiescent current ( bias )??
So I am trying to see what went wrong with the measurements.
I can not make anything with the readings you got. From that resistor you will have three diode voltage drops (be) which would mean you would have around 5 volt left for the quiescent current ( bias )??
So I am trying to see what went wrong with the measurements.
Measured the second time I was definitely on 20V DC (the blue side, pictured) The black lead was in a black negative speaker terminal. Power on, those were the readings it gave me. Perhaps my MM is junk?
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Just got those transistors in the mail. Should I go ahead and replace TR05? And while I’m at it should I replace the one on the other channel too or leave it alone? Waiting on your thoughts before I continue.
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Can we be 100% sure about this? I will absolutely swap them around. But I need to be 100% sure they go in backwards before I proceed.
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Ignore this post. I see what you mean now. Emitter and base. I got it
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Installed the new transistor in TR05. VR01 won’t adjust at all. DBT dims then flashes, then stays lit. VR02 still adjusts to the correct bias. That channel seems fine.
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GrisPato
Super Member
Mhhh, I had a feeling already it wasn't tr05.
I am still stumped by the 6-7 volt readings you had on r29-30.
If I just forget that I was expecting around 2 volt and just compare the 2 channels then the lower voltage ( -0.850 V) in the left channel is caused by the excessive current.
So then something downstream is not functioning correctly.
I am still stumped by the 6-7 volt readings you had on r29-30.
If I just forget that I was expecting around 2 volt and just compare the 2 channels then the lower voltage ( -0.850 V) in the left channel is caused by the excessive current.
So then something downstream is not functioning correctly.
What could it be? There are only so many things downstream? I’m stumped as to what to do next. This thing has become a headache but i feel I’m either so close, or so far away.
GrisPato
Super Member
Then, as I always do with everything I do myself in equipment, what did I touch and what could have gone wrong with that.
So driver and outputs are replaced.
Are all mica insulators good?
Pinouts, the TO-3 cases can just be installed one way. I think I checked placement of NPN and PNP but can check again. This also for the drivers.
So driver and outputs are replaced.
Are all mica insulators good?
Pinouts, the TO-3 cases can just be installed one way. I think I checked placement of NPN and PNP but can check again. This also for the drivers.
GrisPato
Super Member
Plenty