Right channel problem. No sound. Intermittently TP measures 10 v and not 2.7 v. Voltage across R66 is 3.3 mv
Which TP? TP9 ? R66 voltage drop seems too low so presumably some parts of the AD744 are being de-biassed.
In order to be sure the problem's around the AD744 I need to know if TP7 is still ~5.5V? (that's measured with the filter plugged in).
In order to be sure the problem's around the AD744 I need to know if TP7 is still ~5.5V? (that's measured with the filter plugged in).
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Assuming its 7.9V with the filter out then re-check all resistor soldering around U8. Check voltages on pins 2,3 and 5 of U8.
Redo R joints around AD744. Now TP measure 2.6 v but when power off and on TP 9 reverts back to 10v!
Based on your AD744 voltage readings the opamp is working fine. The puzzle is how its possible for pin2 to be 0.64V when TP7 is still 7.9V. Best guess is a short across one of the caps C47-C50. Or the opamp's failed in such a way as to put a low voltage on pin2.
I intend to remove C47 to C50 one by one and measure the voltage at TP9.
Is this logical?
Will do tomorrow morning.
Is this logical?
Will do tomorrow morning.
I think if they don't show short on a meter try replacing AD744. I haven't ever had an NP0 fail short, X7R does quite often though.
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C49 may be the culprit
Replaced AD 744. Rather scary procedure without hot air gun. Have to use 2 soldering irons.
Problem persists after AD744 change. The pins of the op amp is dirty and refuse to bind to solder. Have to use blade to scrap off the dirt.
Direct attention to C47 to C50.
Remove c49 and immediately TP 9 measure about 2.5v
Replaced AD 744. Rather scary procedure without hot air gun. Have to use 2 soldering irons.
Problem persists after AD744 change. The pins of the op amp is dirty and refuse to bind to solder. Have to use blade to scrap off the dirt.
Direct attention to C47 to C50.
Remove c49 and immediately TP 9 measure about 2.5v
Attachments
C49 measures 2.4nf.
I notice that TP 9 voltage would measure 2.5 v on power up immediately and suddenly jump to 10 v after a while prior to the change of c49
I notice that TP 9 voltage would measure 2.5 v on power up immediately and suddenly jump to 10 v after a while prior to the change of c49
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C49 must have some shunt resistance otherwise removing it couldn't affect the DC level. Hence an ohmmeter (rather than capacitance meter) check would be instructive.
OK so the cap hasn't failed. Problem must be either a solder filament across it which melted away when you removed it or similar on the PCB itself.
I think l need more practise soldering smd.
It sound very very good. Hearing microdetails that l wonder whetherit is my imagination or not.
When music is playing, l hear random low level noise such as switching on and off individual tracks in a multitrack recording. I am uncertain whether this is in the recording or a distortion.
I don't hear this distortion when l pause or stop music. I am using mediamonkey or VLC player
It sound very very good. Hearing microdetails that l wonder whetherit is my imagination or not.
When music is playing, l hear random low level noise such as switching on and off individual tracks in a multitrack recording. I am uncertain whether this is in the recording or a distortion.
I don't hear this distortion when l pause or stop music. I am using mediamonkey or VLC player