If you haven't taken this thing out back ans shotgunned it to death yet...
Remove all 3 muting transistors. Power up the amp (all transistors clamped down to prevent overheating) and monitor the DC voltage on pad 3 of the muting transistors in the audio section. What does the voltage go down to?
Does it remain there as long as the amp is on (longer than you've left it when the mute circuit acted strangely)?
Remove all 3 muting transistors. Power up the amp (all transistors clamped down to prevent overheating) and monitor the DC voltage on pad 3 of the muting transistors in the audio section. What does the voltage go down to?
Does it remain there as long as the amp is on (longer than you've left it when the mute circuit acted strangely)?
I've certainly considered doing that to it! At this point determination to fix it has set in though.
Erratic would best explain the readings I got. The voltage eventually dropped to -16.5v after roughly 15 minutes of play. To explain the erratic part of it...it doesn't hold there, it bounces up and down continuously(going back up as far as -8.5v). The voltage was doing that entire time through out the testing...it wasn't a continual drop but up and down. Also, at one point in the middle of testing, I was getting different readings from the two, one being at -6.5v(right side in pic) the other at -2.5v.(left side in pic). Given what you said earlier about negative voltage on this circuit... upon turning the amp on, the readings were +2.5v but immediately dropped into the negative range. Hoping you can make something out of it all...
Erratic would best explain the readings I got. The voltage eventually dropped to -16.5v after roughly 15 minutes of play. To explain the erratic part of it...it doesn't hold there, it bounces up and down continuously(going back up as far as -8.5v). The voltage was doing that entire time through out the testing...it wasn't a continual drop but up and down. Also, at one point in the middle of testing, I was getting different readings from the two, one being at -6.5v(right side in pic) the other at -2.5v.(left side in pic). Given what you said earlier about negative voltage on this circuit... upon turning the amp on, the readings were +2.5v but immediately dropped into the negative range. Hoping you can make something out of it all...
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Confirm:
0 ohms between any secondary side transformer winding and the striped side of the diode.
0 ohms from the other end of the diode to the 100k resistor.
0 ohms between the second end of the 100k resistor, the negative terminal of the cap and the gate pad for at least one of the muting transistors in the audio section.
0 ohms between any secondary side transformer winding and the striped side of the diode.
0 ohms from the other end of the diode to the 100k resistor.
0 ohms between the second end of the 100k resistor, the negative terminal of the cap and the gate pad for at least one of the muting transistors in the audio section.
I have some questions:
Which diode are you referring to? One of the two I just replaced or both?
Which are the secondary side transformer windings?
Which end of the 100k is the second end?
Also, when checking the diode/diodes(non striped end) to the 100k transistor, does it matter which end of the resistor? (I'm getting different readings from the two ends of the resistor).
Not knowing that I did check it all(using all transformer windings and on both sides of the resistor). I am getting ohm readings either way. Knowing the answer to the above questions I can give you those readings.
Which diode are you referring to? One of the two I just replaced or both?
Which are the secondary side transformer windings?
Which end of the 100k is the second end?
Also, when checking the diode/diodes(non striped end) to the 100k transistor, does it matter which end of the resistor? (I'm getting different readings from the two ends of the resistor).
Not knowing that I did check it all(using all transformer windings and on both sides of the resistor). I am getting ohm readings either way. Knowing the answer to the above questions I can give you those readings.
You ain't going to believe what's been causing all of the problems.
The black cap for the positive regulated voltage leaked (conductive) electrolyte that leaked positive voltage from the positive supply to the mute drive, preventing it from going down. Clean the area with acetone and a cotton swab between the cap and the pad indicated by the arrow.
The black cap for the positive regulated voltage leaked (conductive) electrolyte that leaked positive voltage from the positive supply to the mute drive, preventing it from going down. Clean the area with acetone and a cotton swab between the cap and the pad indicated by the arrow.
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