How to test TDA7379 audio power amp

Thread Starter

neospam

Joined Jan 13, 2020
110
If you can post clear pictures of the parts you're trying to identify, pictures that show the marks, then we can help.

Keep in mind that voltage is relative. Your scope measures voltage on the probe tip relative the ground for that channel. On most scopes, the channel grounds are also connected to the ground in the power cable, so if the ground clip is disconnected then the probe tip voltage will be relative the wall outlet ground (on most scopes, there are exceptions such as scopes with isolated inputs and battery powered scopes) . The net effect of leaving the ground clip off is all that wire in the power cord and the wall becomes an antenna and really affects your readings in a bad way, and the higher the frequency you're measuring the more your reading is affected. So in short, if you want an accurate reading, you must use the ground clip, and clip it as physically close as possible to where you're taking the reading. On a low frequency like 1kHz, any ground point on that amplifier board is probably fine.

This will be helpful :
 

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Thread Starter

neospam

Joined Jan 13, 2020
110
Had my one tester hooked up wrong. I retested the power cap, the one cap I thought I broke and 2-trans that I thought were bad, they are good. Soldered them back in.

p.s. One trans was a CBE and the other CEB
The GRD cleaned up all the AC interference.

I put a 1Hz square wave into audio input, that's the lowest it goes. With the scope I just see a voltage pulse, voltage no-voltage pulse, no square wave.
 
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MrSoftware

Joined Oct 29, 2013
2,188
1Hz is too low for audio. I haven't seen the schematic for that amplifier, but many amplifiers will include a subsonic filter that will filter out frequencies too low to hear. I would put 1kHz in and follow that through the circuit.
 

Thread Starter

neospam

Joined Jan 13, 2020
110
TDA7379 with 1hz 0-2v signal. I get a clicking on and off through speaker, very slight. I scoped the speaker output. see scope pict, little blurry. scope settings 5mV, time 0.5uSec

TDA pinout -
1 & 2 - outputs get 2v pulse
3 - vcc getting 17-18v
4 - 9 getting 2v pulse
10 - diag 0v
11 & 12 2v pulse
13 - vcc 17-18v
14 & 15 - outputs 0v
 

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Audioguru again

Joined Oct 21, 2019
6,673
Your 'scope timebase is 1000 times too short to show 1kHz sinewaves. If you set the timebase to 0.5ms (500us) then you will see one sinewave for each two divisions.
 

bertus

Joined Apr 5, 2008
22,270
Hello,

Do you really use a 1 Hz signal?
That will not pass the capacitors.
Use a 1 kHz sinewave signal for testing, as the others suggested.

Bertus
 

Thread Starter

neospam

Joined Jan 13, 2020
110
1Hz is too low for audio. I haven't seen the schematic for that amplifier, but many amplifiers will include a subsonic filter that will filter out frequencies too low to hear. I would put 1kHz in and follow that through the circuit.
I do get a similar square wave across most of the pins on the TDA. There are 4 outputs (1&2, 14&15), Pins 1&2 have a similar square wave pattern as the other pins. I think something might wrong with pins with the output on 14 & 15. I4 has a weird wave pattern see below and 15 has no signal. Used 1 kHz low 0-2v range, mostly around 2v.

This unit has 3 speakers, 2 stereo speakers and sub. All 3 speakers you can hear a tone from the signal.

last pict might be the same wave.. took these a while ago and was working on something else.
 

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Audioguru again

Joined Oct 21, 2019
6,673
Your squarewaves show severe high frequency peaking maybe because you have your 'scope probe set to x10 attenuation and it is badly over-compensated?

Pin 15 should have the same output as the other outputs so it is dead or its input is not connected.the voltage gain of the amplifier is 20 times so your 2V input level is much too high.

Here is how to adjust your 'scope probe:
 

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MrSoftware

Joined Oct 29, 2013
2,188
The output should look exactly like the input, just more amplitude. As mentioned above, if you turn the input up too much and the amplifier cannot keep up, the output will be clipped. Connect 2 scope probes, one to the input and one to the output and compare. They might be out of phase, but the shape should be the same. If the amplifier has a high pass or low pass filter on any of the channels then that can attenuate the output. For example, if your sub has 100Hz low pass filter then very little of the 1kHz will show up on your sub channel, that is normal.

If you're hearing output on the speakers, what is the problem that you're trying to correct?
 

Thread Starter

neospam

Joined Jan 13, 2020
110
The output should look exactly like the input, just more amplitude. As mentioned above, if you turn the input up too much and the amplifier cannot keep up, the output will be clipped. Connect 2 scope probes, one to the input and one to the output and compare. They might be out of phase, but the shape should be the same. If the amplifier has a high pass or low pass filter on any of the channels then that can attenuate the output. For example, if your sub has 100Hz low pass filter then very little of the 1kHz will show up on your sub channel, that is normal.

If you're hearing output on the speakers, what is the problem that you're trying to correct?
thanks.. I will try what you both recommended later today. Problem is that its dead, has remote turn on pwr, vol, adj, led.. dead, no LED nothing. Tone is from the function generator, very slight and there is no control over volume by the speaker controls. For myself, learning problem solving is what I wish to learn and this is fun for me. If it works, it's a much better sounds system for my computer system that I am using now.

Your squarewaves show severe high frequency peaking maybe because you have your 'scope probe set to x10 attenuation and it is badly over-compensated?

Pin 15 should have the same output as the other outputs so it is dead or its input is not connected.the voltage gain of the amplifier is 20 times so your 2V input level is much too high.

Here is how to adjust your 'scope probe:
Most of the pict were 1x, though a couple pict were from when it was on 10x.
Probes were adj, will ck again today. I just recently fixed my Cal Out on my scope and was able to adjust my probes. Not trying to jump ahead, what cause high frequency peaking, bad cap if its not the probes?
.
 
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Audioguru again

Joined Oct 21, 2019
6,673
Does the repaired Cal Out on your 'scope produce a perfect squarewave with sharp corners when the probe is switched to 1x?
Maybe the Cal Out attenuates high frequencies and you adjust the probe's 10x to peak it back to normal.
Maybe the repair also peaks the probes 1x?

Measure the squarewave from your signal generator on 1x and on 10x to see if it has rounded corners.
 

Thread Starter

neospam

Joined Jan 13, 2020
110
Some switches are dirty and need to be cleaned, kind of a pain on one of them.

1 probe is on signal coming in & 2 probe on speaker. Top wave is speakers, bottom wave is input signal.

The first pict. @ 100Hz signal & no power to the unit, when you turn it on nothing changes. Although the function generator signal from the input disappears from the scope when you turn it off so that means the switch is working. The 2nd pict was at 80Hz, that's when the signal curved quite a bit, power on off no change. This was at less then 1v (my FG does not have voltage readout), guessing by specifications low = 0-2v, it was at about 1/4 turned up.
 

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Thread Starter

neospam

Joined Jan 13, 2020
110
Does the repaired Cal Out on your 'scope produce a perfect squarewave with sharp corners when the probe is switched to 1x?
Maybe the Cal Out attenuates high frequencies and you adjust the probe's 10x to peak it back to normal.
Maybe the repair also peaks the probes 1x?

Measure the squarewave from your signal generator on 1x and on 10x to see if it has rounded corners.
I will compare it to the function generator. I was told that the left hand side of the wave will curve with a 20Mhz scope? I will compare the two and get back.
 

Audioguru again

Joined Oct 21, 2019
6,673
You did not say if the amplifier's input probe is set to 1x or to 10x.
If it is set to 10x then the compensation adjustment causes too much high frequency peaking.
If the probe is set to 1x then either the signal generator or the 'scope is causing the high frequency peaking.

The slant of the squarewave is normally caused by very low frequencies being attenuated with normal phase shift.
The curve of the squarewave is caused by mid and high frequencies being attenuated but the high frequency peaking is still there.
 

Thread Starter

neospam

Joined Jan 13, 2020
110
You did not say if the amplifier's input probe is set to 1x or to 10x.
If it is set to 10x then the compensation adjustment causes too much high frequency peaking.
If the probe is set to 1x then either the signal generator or the 'scope is causing the high frequency peaking.

The slant of the squarewave is normally caused by very low frequencies being attenuated with normal phase shift.
The curve of the squarewave is caused by mid and high frequencies being attenuated but the high frequency peaking is still there.
when I cal, need to set to 10x, other wise using 1x. here pict of cal out sq, and function gen sq. To cal the probe it is 10x as in pict.
 

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Thread Starter

neospam

Joined Jan 13, 2020
110
Your sig gen and 'scope work well so it must be the amplifier circuit that is messed up.
if you don't think anything works right let me know. I just got the FG and scope not to long ago. Have found manuals for the FG, have some close that are for the scope.

Today, will be receiving a E-TDA7379 from digkey. Keep fingers crossed, by swapping it out and putting power to it?
 

Thread Starter

neospam

Joined Jan 13, 2020
110
Replaced the TDA7379 and nothing. I rather diagnose what going on then replace parts, just not sure how to test some of this stuff. Unit still act dead.

The circuit has more IC then this chip. I uncovered from glue (thought they were resistor banks) after closer look and removing the glue I noticed they had several pins and are vol controls - m51132L. Not sure how these work, but thinking they feed the TDA7379, not sure and looks to be one for each channel. They also have OpAmp - RC4558P and another OpAmp - NJM4556AD. One number I already crossed to a new version, it was outdated.

Unit has wall transformer 2-wire feed that outputs AC 12Vac 3amp to device.
All transistors tested ok, I pulled and tested. Power rect test good, pwr cap test good. Power on the board is not everywhere. On the M51132L, pin 1 Vcc suppose to be 8-15v, rated 12v. I test under 8v at pin 1. It's hard to find pin 1 location on the circuit board. There is a 'A' marking and believe that is pin 1. opposing pins - Pin 13 & 14 are out & In, both should be below 5.5v

Don't know if someone can explain what IC are doing and feeding what other devices. what is the role of the OpAmp in the circuit? Not sure that can be answered very easy.
 
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