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JBL BP1200.1 no audio
JBL BP1200.1 no audio
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Old 25th July 2017, 07:03 PM   #21
Formas is offline Formas  Jamaica
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Join Date: May 2008
I've place that ic in a socket from before I start this thread I've toggled with the original and replacement. I can post the voltages for the pins, I seriously think I'm having a bad caps issue. As I mentioned before if left idle for a time it left from no audio to choppy audio to clear audio, if it's turn on within let's say 5 mins it appears ok but left for long periods then it's a booting process again.
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Old 25th July 2017, 07:07 PM   #22
Perry Babin is offline Perry Babin  United States
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Join Date: Nov 2003
Location: Louisiana
Confirm that you have clean audio at the input of the LM361 when you think the audio would be non-existent to choppy.

Check for drive at the output transistors (positive and negative) through that same period of time.

Do you see the same failure to function normally either at the LM361 or at the outputs?
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Old 26th July 2017, 11:30 PM   #23
Formas is offline Formas  Jamaica
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Join Date: May 2008
I would have seen a constant sine wave at pin 3 (input pin) only gives a vibration motion on the oscilloscope when the audio is inputted, what ground reference should I used to check it as I was on the CTground I’ve also noticed I’ve gotten a different wave profile when I used the preamp ground to test for audio in this amp. I think I’m a bit lost during this phase.
What would the drive be referring to at the output transistor (both negative and positive) I’m just a bit lost at that level. Help.
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Old 27th July 2017, 03:51 PM   #24
Perry Babin is offline Perry Babin  United States
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
The secondary ground is a good reference point.

The output drive will be a 10 volt square wave driven from the rail voltage (down for positive rail, up from negative rail).

Check for audio on pin 1 of U104. Leave pin 3 of the LM361 grounded.
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