I have a MTX 7402 that came in after someone else attempted a repair on it. I corrected a bunch of issues and got it operational, with one channel performing flawlessly, and the other channel with the pictured interference. This interference exists whether or not any signal is being fed into the RCA's. This interference is not present at the input sides of the NE5532. The NE5532 has been replaced three times just to make sure I don't have a bad one. And the frequency of the interference suggests that it is from the power supply switching. This made me want to investigate grounds on the channel with the fault however have not been able to locate anything specific. Diodes also appear fine. Any help or suggestions would be very much welcome.
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I have not but will do that tomorrow.
I did check the signal coming out of the preamp going to the NE5532 and it appeared clean. But as said will bypass the preamp tomorrow
I did check the signal coming out of the preamp going to the NE5532 and it appeared clean. But as said will bypass the preamp tomorrow
Yes the noise remains with the board bypassed and even with the board removed entirely.
When you zoom into the noise, it occurs at 40kHz in time with the power supply switching.
When you zoom into the noise, it occurs at 40kHz in time with the power supply switching.
Which terminals did you jump when bypassing the preamp board?
With no jumpers and no preamp board, do you see noise on the bad channel?
With the preamp board connected normally, do you see the noise on the bad channel with no signal source connected?
Can you post a close-up, high resolution photo of the bad channel section of the main board?
With no jumpers and no preamp board, do you see noise on the bad channel?
With the preamp board connected normally, do you see the noise on the bad channel with no signal source connected?
Can you post a close-up, high resolution photo of the bad channel section of the main board?
See the attached picture for terminals being jumped. Red circle is the right side signal input, white circle is left signal input, orange circle is preamp boards output. I tried jump both reds to the right ornage and both whites to left ornage. Noise is even worse on the oscilliscope with it jumped.
Next picture is zoomed in on the oscilliscope with preamp completely disconnected.
Last picture is the faulty channel and its components on the other side of the board
Next picture is zoomed in on the oscilliscope with preamp completely disconnected.
Last picture is the faulty channel and its components on the other side of the board
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Do you have signal on the white jumper?
Do you have this noise on the input to one of the channels (C400/C500)?
Do you have this noise on the input to one of the channels (C400/C500)?
As long as i have the left RCA jack into the amp, then yes the white circled wires have signal.
Yes the noise/interference is present on the veer leading up to C500. I cant find any signal on the other side of C500. (Is that side connected to ground?)
C400 has no interference.
Yes the noise/interference is present on the veer leading up to C500. I cant find any signal on the other side of C500. (Is that side connected to ground?)
C400 has no interference.
veer?
Are you saying that you have no signal between the terminal of C400 and the 3.32k resistor?
What about on the other channel?
If you plug in only one RCA at a time, which color jumper corresponds to the right channel?
Is the whits jumper the only one that has signal when the left RCA is plugged in?
Are you saying that you have no signal between the terminal of C400 and the 3.32k resistor?
What about on the other channel?
If you plug in only one RCA at a time, which color jumper corresponds to the right channel?
Is the whits jumper the only one that has signal when the left RCA is plugged in?
Im operating off of memory currently but there was no signal going to R400 (or R500 on the working channel) so i had assumed that was normal. (I will double check this tomorrow).
And yes, the white circled wires carry the left rca signal into the preamp board and red circled wires carry the right rca signals to the preamp board. When i bypassed the preamp, i jumped one of the reds (tried both independantly into the right hand orange circled output line. Conversly i did the same with the left white wires into the left hand orange output line.
Hopefully that clears it up a little
And yes, the white circled wires carry the left rca signal into the preamp board and red circled wires carry the right rca signals to the preamp board. When i bypassed the preamp, i jumped one of the reds (tried both independantly into the right hand orange circled output line. Conversly i did the same with the left white wires into the left hand orange output line.
Hopefully that clears it up a little
I'd expect no signal on the resistor terminal that is NOT connected to the capacitor but would expect to see signal between the cap and resistor.
Do you see the noise at the jumper?
With no jumpers, find the right/left signals. You should see the noise here, as well.
If so, jump the left signal to the right amp input and vice-versa to see if the noise switches channels.
Do you see the noise at the jumper?
With no jumpers, find the right/left signals. You should see the noise here, as well.
If so, jump the left signal to the right amp input and vice-versa to see if the noise switches channels.