Don't know how your going on but if pin 4 has any AC "noise and rubbish" on it that points to the 22 mfd cap C2708 or C2743 depending whether it's left or right that connects to pin4. We know the 5 volts is clean, and pin 4 get's it's supply via a 100 ohm from the 5 volt rail.
I think you said the TDA's were in sockets. Easy to remove. Just prise a little at a time one end, then the other with a thin driver, a millimetre at a time.
Check as Andy suggests that your 'scope it properly grounded and recheck that pin 4. Compare it again with the other channel.
I think you said the TDA's were in sockets. Easy to remove. Just prise a little at a time one end, then the other with a thin driver, a millimetre at a time.
Check as Andy suggests that your 'scope it properly grounded and recheck that pin 4. Compare it again with the other channel.
Attila,
Do you mean around 100 millivolts or between 0 and 1 volt noise? It still sounds suspicious does that to me, particularly if the other IC is clean. Have you got another cap to put across the 22 mfd -- again it's not very critical a 22 to 100 mfd should prove it.
I think you have to swap the TDA's next. It will get them out of the way. With anything like this it may help to carefully go round each TDA with both the DVM and the 'scope and note any major discrepancies. Check each pin alternately in turn, first one DAC then the other. Don't miss any pins out, even the ground pins. Try it also with the CD player paused or in stop mode so that the data to the DAC's is constant.
Do you mean around 100 millivolts or between 0 and 1 volt noise? It still sounds suspicious does that to me, particularly if the other IC is clean. Have you got another cap to put across the 22 mfd -- again it's not very critical a 22 to 100 mfd should prove it.
I think you have to swap the TDA's next. It will get them out of the way. With anything like this it may help to carefully go round each TDA with both the DVM and the 'scope and note any major discrepancies. Check each pin alternately in turn, first one DAC then the other. Don't miss any pins out, even the ground pins. Try it also with the CD player paused or in stop mode so that the data to the DAC's is constant.
Thats fine. Solder a separate ground wire to the PCB ( use the audio ground ) and connect that to the 'scope ground terminal ( usually a large screw on the front panel ) and then forget the probe ground --clip it out of the way so you are not constantly having to reconnect and check the 'scope ground.
Did you swap the I/C's
Did you swap the I/C's
Mooly, is there a huge difference with grounding? I use the separate probe ground from the scope, with a clip on the audio ground of the cd. The scope (Hameg HM1007 has no ground screw!).
I measured signal before and after kill: both left and right are absolutly identical: same amplitude, same period...
Will now go on pin 1 of IC 6673 and 6675. After this I'll have a listening probe of the cd. Then swap the TDA. Should take 20 min!
Edit: pin 1 of NE5532: -3.2 V on both, when cd paused
when playing test tone: same amplitude, same period
I measured signal before and after kill: both left and right are absolutly identical: same amplitude, same period...
Will now go on pin 1 of IC 6673 and 6675. After this I'll have a listening probe of the cd. Then swap the TDA. Should take 20 min!
Edit: pin 1 of NE5532: -3.2 V on both, when cd paused
when playing test tone: same amplitude, same period
HOW WEIRD IS THAT???? 
I just plugged the cd back on the amp: both channels now have full output, no noise, no distortion nothing!!!! Slightly more output on the right (less than 5% I would say) than on left. Before it was 20 to 30% LESS!!!
I'm happy, but would be even more happy if I could find where it's coming from!
I just plugged the cd back on the amp: both channels now have full output, no noise, no distortion nothing!!!! Slightly more output on the right (less than 5% I would say) than on left. Before it was 20 to 30% LESS!!!I'm happy, but would be even more happy if I could find where it's coming from!
You should have no measurable imbalance between left and right.
You need to be logical faultfinding. The Hameg 'scope has a ground pin below the display I think. Connect a wire from here to the audio ground on the PCB which is the ground that goes to the output sockets. This leaves the probe much more manouverable as you don't need connect it's own ground now. Just clip the ground lead out of the way up the cable.
Connect the CD player up to your amp and make sure the fault is present.
Play your test CD -- is this a homemade one or not ? VERY IMPORTANT that the left and right channels have the same signal.
Measure in turn on pins 1 of IC 6673 and 6675. The signal MUST be identical in every way. It may look a little noisy as it's not been through the final filter stage yet.
If it is identical, then check on pins 7 of the same IC --again it MUST be identical.
If this checks out OK and the fault is STILL present ( check that it is ) then it has to be after this point which leaves only the relay and a few passive components.
If the relay "Kill" is playing up this may not show up on the 'scope unless a load is attached to the output sockets. ie your amp.
You have to measure in a logical sequence now, we have done all the guessing - it may be this or that - every measurement has to foward the cause now.
Fixed by tea time then
You need to be logical faultfinding. The Hameg 'scope has a ground pin below the display I think. Connect a wire from here to the audio ground on the PCB which is the ground that goes to the output sockets. This leaves the probe much more manouverable as you don't need connect it's own ground now. Just clip the ground lead out of the way up the cable.
Connect the CD player up to your amp and make sure the fault is present.
Play your test CD -- is this a homemade one or not ? VERY IMPORTANT that the left and right channels have the same signal.
Measure in turn on pins 1 of IC 6673 and 6675. The signal MUST be identical in every way. It may look a little noisy as it's not been through the final filter stage yet.
If it is identical, then check on pins 7 of the same IC --again it MUST be identical.
If this checks out OK and the fault is STILL present ( check that it is ) then it has to be after this point which leaves only the relay and a few passive components.
If the relay "Kill" is playing up this may not show up on the 'scope unless a load is attached to the output sockets. ie your amp.
You have to measure in a logical sequence now, we have done all the guessing - it may be this or that - every measurement has to foward the cause now.Fixed by tea time then
Thanks Mooly!
And I use the ground connector below the display from the beginning!
The test cd is an industrial one, a test cd from a german hifi journal! On test tones the signal on both channels should be the same. Test tones ranging from 20 Hz to 20 kHz.
Didn't know that a load had to be attached to check the kills!
Give me an hour and I'll post the results!
And I use the ground connector below the display from the beginning!
The test cd is an industrial one, a test cd from a german hifi journal! On test tones the signal on both channels should be the same. Test tones ranging from 20 Hz to 20 kHz.
Didn't know that a load had to be attached to check the kills!
Give me an hour and I'll post the results!
_Attila_ said:HOW WEIRD IS THAT????
I'm happy, but would be even more happy if I could find where it's coming from!
Did you swap the dac chips over ?
Andy
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