Hello, I am trying to fix the sound output of my vtech baby monitor. The receiver screen shows that there is audio but nothing comes out of the speaker on the device. Attached is the board. The bottom 2 wires are connected the the speaker, just up from that is an 8 pin dip which is an op amp. Where would you start to troubleshoot this?

I also have another receiver for parts, that the sound works perfectly but it just is not paired to my cameras (it’s also impossible, vtech says, to pair cameras with a different serial number monitor)

Thank you!

 

Did you try using the known good speaker?
I suspect that chip is a class D audio Amp. What is the part # on the chip?

 

Check the speaker first, what is the number of the op amp ,, if you have an extra amplifier you can use it to probe around the test points (tp111+112)to see if the audio is there.

 

You can use a multimeter to test the speaker and see if it is functioning properly. Set the multimeter to measure resistance (ohms) and touch the probes to the speaker terminals. A reading of around 4-8 ohms is normal for most speakers. If the reading is much higher or lower than this, the speaker may be damaged and need to be replaced. You can test the op amp by using a signal generator or audio source to input a signal into the circuit and checking the output using an oscilloscope. If the signal is not being amplified correctly, the op-amp may need to be replaced.

 

Did you try using the known good speaker?
I suspect that chip is a class D audio Amp. What is the part # on the chip?

Yes, I also took that speaker out and tested it. I was hoping it would be something easy like a speaker. The chip # is 8002e / CN7x94 IN

 

I will check the audio amp IC when I get home. It also looks like it goes through some SMD resisters, and then though a diode. Do you all think the audio amp is the best bet for bring faulty just out of the blue one day?

 

Here is the pinout of the 2W Audio chip 8002e

 

Here is the pin out of the 2W Audio chip 8002e
View attachment 289068

Thank you, I did come across that same diagram just a little bit ago.

 

I was trying to test input and output of the audio amp. Every time I press the same button between the 2 units I have they both show the same sign wave output (voltage and duration) on the scope. I did not take the audio amp out since I'd likely destroy it. I tested the speaker yet again, even swapping them between the 2 units. I guess I'm not sure why if they put out the same wave on the scope, one works and the other doesn't.

I also was not able to input the audio amp using a function generator. The ones I have are 5v output for a square wave. The voltage input on the monitors are 1.5v. I suppose I could make a voltage divider but testing it using the buttons on the monitor should do the same test right?

 

Where on the board are you testing the output TP112 and 113? If so sounds like just a broken connection between the Amp output and the speaker. Maybe on the speaker connector.

 

Yes I tested there and on the audio amp pins. I did however get it working. I ended up finding a smd resistor that wasn’t making a connection to the pad near tp113. I must have gotten the signal when I pushed on it while testing. Anyways it seems to be working now. For the time being anyways. Happy wife happy life now. Thanks for the help everyone.