I don't remember any 44v in c352? D124 (green led near IC105?) must be on.
did you control all voltages, +-50v for amplifier, +-37v for preamplifier, 5.6v (IC401). Are input selection leds and buttons working?
Where do you measure 44v ? It must be 50v I think. Disconnect P102B and measure voltage.
Test br101 if it's bad, test C154&C155.
On board there are some cable connections (on board like resistors but here there is only nake cable), voltage wrote on it. test them with ground.
On disconnect P102B
Pin1 -50V
Pin2 +40.5V
No 5.6v on IC401... Its 7.16v
Where I need test 37V....
Pin1 -50V
Pin2 +40.5V
No 5.6v on IC401... Its 7.16v
Where I need test 37V....
BR101 is OK
C154&C155 are OK.
Why the green led D124 is off?
Why any led or knob on front panel no works?
C154&C155 are OK.
Why the green led D124 is off?
Why any led or knob on front panel no works?
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There are 4 fuse. Are all working? pin1 &pin 2 are equal and must be near +-50v. 40.5 volt says something wrong in power supply. Also disconnect P101b. If voltages are still different. Work around the psu.
IC401is LM7805 it gives 5.6volts. not 7volts. D401 may be fault. or LM7805.
But, those two fully different and not connected circuits. How can be both have problems?
It's dangerous to play with 100volts. you have to be very carefull. C407&8 stores voltage! Wait for discharge.
(on BR101, there are two ¨ signs and - and + sign. what is the value of voltage between + and -. I remember that it was near 80v, but not sure. I don't want to open c352 now).
IC401is LM7805 it gives 5.6volts. not 7volts. D401 may be fault. or LM7805.
But, those two fully different and not connected circuits. How can be both have problems?
It's dangerous to play with 100volts. you have to be very carefull. C407&8 stores voltage! Wait for discharge.
(on BR101, there are two ¨ signs and - and + sign. what is the value of voltage between + and -. I remember that it was near 80v, but not sure. I don't want to open c352 now).
D124 off because IC105 is in protection mod. Or really there is no power.
front panel no works? Because, there is problem with 5.6v supply. And may be more problems in front panel.
where can I control 37v......I can't find
I think is +18v & -18v......for preamp.....
I think is +18v & -18v......for preamp.....
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I'm thinking Q155/Q158 are the ±18 V regulators. They're on the bottom of the power amp schematic. I bet the +12 V "regulator" is the voltage divider formed by R254, R255 and emitter followers Q159, Q160. They're fed from the +18, so once you get the ±18 V rails working, the 12 V will probably spring to life as well.
Tom
Tom
Check all theses r680r and the opposite 33r resistors I highlighted. In my experience, these 680r go high, usually 1-2k and it causes excessive current on these 33r resistors and triggers protection. You can check them in circuit if you can get to them, you are just trying to verify if they are open or high resistance.
Attachments
Check those 680r resistors nearby, there had to be a reason that zener died. R247, R249, R248 and R250