Wireless Lekato WS50, no sound but

[x-pro]

Your skills are commendable.

[ricci]

Your skills are commendable.

come on now don't make fun of me ... electronics is just a hobby, I know my limits

[ricci]

I am almost certain that it is the receiver that is not working, in fact without a diagram I thought of checking if the signal reaches the receiver, so I identified the two converters, the analog-digital ES7243 one on the TX and the MS4344 Dac on the RX, I injected in the TX a 1khz analog signal and I verified that this arrives at the two pins 9 and 16 of the ES7243 ADC, so the problem is not in the input-ADC path. The signal comes out digitized from pin 3 of the ADC (I only see a sort of wave train) and I find it on pin 1 of the serial input of the MS4344 converter and from here an analog signal finally comes out from pins 7 and 10, again 1khz even if with lower Vpp at the start.

I find the signal up to the IC 21BLg which has 5 pins, it is located just before the output but I have not found any trace online and no datasheet.
I think the problem is in the last path of the RX, the one circled in red.

[g1]

Now that you have got to the analog section of the receiver, you can go back to your working unit and inject same 1Khz signal and follow along to the output for comparison.

[ricci]

Today I was thinking the same thing, to disassemble the new working unit, but it's not easy.

Edit: open

[ricci]

The circuit of the new one has changed, different components.

So, let me start by saying that both the ADC and the DAC are stereo. So, I inject 1khz at a voltage of 1V and in both pins 7 and 10, which are the left and right analog outputs of the old receiver, I read about 800mV, while in the new one I read 1.6V, so it seems that the Dac circuit amplifies the signal which then normalizes to 1.2V at the output.

Edit:

I also compared the pins of the two DACs, only the clock in pin 2 changes, in the old one it is 3Mhz while in the new one it is just under 1Mhz.

[ricci]

Solved the problem of no sound at the output, the cause was the 21BLg IC, an LMV321B op amp which after desoldering it I saw had the pin 4 output grounded. However i think that the MS4344 DAC also doesn't work well because, testing the unit without the LM321, the output audio is there but it's those 800mV that come out of the DAC, 200mV less than the 1V input, so there is a slight drop in volume.

[The Dude]

It's not uncommon for a DAC to have lower output than input (depending on input level). The front end often has a compressor/limiter built in to guard against digital clipping. I haven't actually researched that particular chip or looked at data sheets, but it's something you might investigate before condemning the chip.

[ricci]

In the new device had as a replacement, the dac Vpp is around 1.8v, really almost double the 1V input signal and more than double the 811mV of the faulty DAC under investigation.

In the order:

Direct cable
DAC working
Bad DAC

[ricci]

I fixed it. First of all I had the lm321 opamp broken, pins 2&4 shorted, I replaced it but it still didn't work, then since the opamp is not present on the new model where the analog output of the DAC goes almost direct to the audio output of the RX, I did the same by cutting some tracks on the old model and now the signal I have at the TX input is the same as the one at the RX output.

[nosaj]

That's awesome and a lesson in persistence.
nosaj

[ricci]

Never give up !