I repair the output and power supply sections.Amp powers up and plays good audio but I can hear some squealing noise coming from the transformer .
Twisting the transformers doesn’t stop the noise.PS FETs on one side of the board gets warm while the other side stays cool.Drive signal look ok but it looks like some frequency interference on the side that is getting warm.
many suggestions?
10v/dv 10/us
Twisting the transformers doesn’t stop the noise.PS FETs on one side of the board gets warm while the other side stays cool.Drive signal look ok but it looks like some frequency interference on the side that is getting warm.
many suggestions?
10v/dv 10/us
Attachments
Frequency interference?
How does the drive from one side compare to the drive on the other side? Look at the signal on the gate leg of every PS FET.
When you display the waveform, you want it to use bout 3/4 of the waveform (from ground up for this waveform) and to show about 3 complete cycles.
Is this displaying 2 channels or is it a problem with the triggering of the scope?
How does the drive from one side compare to the drive on the other side? Look at the signal on the gate leg of every PS FET.
When you display the waveform, you want it to use bout 3/4 of the waveform (from ground up for this waveform) and to show about 3 complete cycles.
Is this displaying 2 channels or is it a problem with the triggering of the scope?
Drive signal on both sides look the same.
Only one channel is displaying on the scope in the pic ,what you seeing is another wave coming in and out according to the noise coming from the transformer .
Only one channel is displaying on the scope in the pic ,what you seeing is another wave coming in and out according to the noise coming from the transformer .
Did you try decreasing the vertical amplifier setting on the scope and adjusting the trigger level to get a lock on the waveform?
The two transformers are getting the same drive signal so I can't see that being the cause of one making noise, especially if the drive on the gates of the FETs is identical.
If you squeeze the windings round various parts of the transformer, does the noise change?
The two transformers are getting the same drive signal so I can't see that being the cause of one making noise, especially if the drive on the gates of the FETs is identical.
If you squeeze the windings round various parts of the transformer, does the noise change?
Squeezing the transformer doesn’t change the noise.
I now found out probing pin 4 in the 494 make the noise get way louder and also amp is drawing more current.
I now found out probing pin 4 in the 494 make the noise get way louder and also amp is drawing more current.
There is only one wave; it looks like a problem with scope triggering.
Try increasing the display level and play with triggering (slope, level, pos slope, neg slope, or try to find another stable waveform with another scope channel and trigger on that channel.
First and foremost you want a nice stable display.
Jan
The square wave is stable.The pic I posted is what it looks like when the transformer start making noise
Looking at my notes i repaired a smillar amp with that same problem and it had to do with the timing resistor.I will get a frequency meter to see what is happening.
It may, it may not. If you can't be bothered to properly trigger the scope, who knows?
Jan
If the 33k resistor is the only component connected to pin 4, connecting a 1000pf cap across that resistor may make it more stable.
In parallel with the resistor is an empty pad for a cap which was never populated.
Adding the cap makes it more stable,I can probe pin4 now with no additional current draw.
I am going to drop the frequency down to 26khz what do think?
Adding the cap makes it more stable,I can probe pin4 now with no additional current draw.
I am going to drop the frequency down to 26khz what do think?
1.1/(Rt*Ct). Page 5 of the datasheet.
That will be the oscillator frequency (pin 5). The frequency on 9 or 10 will be 1/2 of the oscillator frequency
That will be the oscillator frequency (pin 5). The frequency on 9 or 10 will be 1/2 of the oscillator frequency