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Author Topic: SHURE SM58 + T4N-NB (microphone + receiver) do not communicate  (Read 1351 times)
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cicos
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« on: May 25, 2021, 03:23:20 15:23 »

A combination
Diversity Receiver: T4N-NB 175.000 MHz (SHURE)
Microphone: SHURE SM58

They do not communicate with each other. Is there a way to check which of the components is defective or both are defective.
After using the device, it is turned on the next day and there is no communication.
I have nothing to check if the microphone emits a signal towards the base,
Can you advice how to check the correctness of the device without expensive equipment?

Device images:
https://mega.nz/file/hl9ElBCb#tKJnRucVEMZYPe_IXsyxuFtTSOp572TO3R5l0IPq-TY

WBR JaMi

I apologize for my poor English.
*** Google translate  ***
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h0nk
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« Reply #1 on: May 25, 2021, 09:51:12 21:51 »

Hello cicos,

buy a DVB-Stick with the RTL2832U Chip.
(This should read: It must contain the RTL2832U Chip.)
Install SDR# and tune to 175 MHz.
Thats all.

Good Luck, and

Best Regards

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cicos
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« Reply #2 on: May 27, 2021, 09:47:37 21:47 »

Thanks for help.

I already have one stick that uses the RTL2832U Chip.
https://www.aliexpress.com/item/32953327598.html
The first attempt after I bought this device was discouraging.
Windows recognized the device but was unable to communicate.

Now I was more persistent I think that after installing the driver and program AIRSPY SDR @ Studio
communication succeeded. When the microphone is turned on (Audio switch off) I get this in Figure 1.

when i turn on the audio switch i get this in picture 2.

It seems to me that it "escaped" a bit with 175,000 MHz, but it doesn't seem like much to me and that Rx and Tx are not visible.
I hope I explained this the way it happens and translated the translator correctly.

How do I test a T4N-NB receiver?

WBR, JaMi
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h0nk
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« Reply #3 on: May 28, 2021, 05:06:16 05:06 »


Hello cicos,

i think that the transmitter uses Wide Band Frequency Modulation
similar to FM Broadcast stations. And 175 MHz could also mean
"around" 175 MHz. Basically the transmitter is working and the
deviation should not be meaningful.
The best instrument to test the receiver is indeed Your microphone.
If the receiver works as superheterodyn receiver, You should be
able to see the output of the oscillator which is used to mix the
microphone signal to the IF (intermediate frequency) with Your SDR.
Check at 185.7 MHz and 163.3 MHz for a carrier if the radio is
switched on. (175 MHz +/- 10.7 MHz).


Best Regards





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cicos
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« Reply #4 on: May 28, 2021, 06:38:53 18:38 »

Hello,  h0nk

I don't have any of the instruments needed for such a complicated device.
I have some kind of schematic only of the microphone part but I have nothing from the base part.
From this I can only conclude that the problem is in the reception area.
I don't have another microphone that works on the same frequency so I can see if something is broken.
I don't know how to use the microphone as an aid because I don't know where in the reception area
to see if a signal is coming. And I don't know how to use SDR to help me only if it can generate a signal that I doubt.
  My knowledge of high frequencies is modest.
Thank you for your desire to help me.

WBR, JaMi

I apologize for my poor English.
*** Google translate  ***
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Checksum8
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« Reply #5 on: May 29, 2021, 12:22:34 00:22 »

Hi Cicos

That is a very old unit. I repaired one of those around 1986? It is a superhetrodyne receiver with a 10.7mhz IF. As I recalled it used a MC3357 or MC3362 IC to demodulate the RF signal to audio output.

Because of the age it may not be an RF problem? It could be bad electrolytic capacitors. Very common in old equipment. Maybe the line out audio amplifier is faulty? Corroded connectors or switches? Look up the data sheets for the IC's and see if they have the right voltages on the supply pins.

Look for burn spots on the pcb and swollen electrolytic capacitors.


Good luck
ciao
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cicos
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« Reply #6 on: May 31, 2021, 08:52:57 20:52 »

Thanks for help.
  Supply voltages are + 10V (+ 9.95V) except for PIC12C672 (supply voltage + 5V).
After turning on the receiver on pin 8 (LA1145M) I have noise. When I turn on the microphone, the noise disappears.
When speaking into the microphone on the mentioned pin 8 (AF output) I have a sound signal which is very weak.
The AF goes to the first of the three MC33179s and there is no output from the receiver.
I'm starting to suspect the PIC16C672 is blocking a signal (If the PIC has that capability in this device).
Any new ideas?

Best Regards,
JaMi
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Checksum8
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« Reply #7 on: June 01, 2021, 12:00:58 00:00 »

Good progress, this is a newer unit than I worked on, there was no pic chip.

If I understand you correctly. The receiver is working, because you are getting AF from the demodulator LA1145.  It could be a bad amp in one of the MC33179's? The pic may be part of the audio squelch or mute circuit, and as you say blocking the signal. If the pic is bad there is no way to replace it without code. You could try  monitoring the logic state on each gpio, to see if  there is any change when turning the microphone on or off. Are the ic's surface mount?
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cicos
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« Reply #8 on: June 03, 2021, 09:21:44 21:21 »

The PIC includes LEDs for A and B "channel" but as far as I can see it is not only the PIC that decides whether the LED will light up.
Via the transistor with LA1145M (pin16) the LED can be switched off and on that pin 16 comes the signal from LP 339 ...
The problem is the fact that I don't have a SCH from the receiver so tracking the connections is very difficult.
In fact, only 3 of the PIC pins are used for the device itself, two for the LED and the third for the signal obtained from pin 17 (LA1145M) ...
Pin4 of the PIC is connected via a resistor to + 5V, Mon 6 to ground and pin 5 is not used.
All LA voltages are within the limits given in the DataSheet but that obviously doesn’t have to mean much.
DataSheet is quite confusing to me because it describes both La1145 and LA1145M, so it's a little harder to understand what's related to "M and no M".
Apart from 3 pieces of MC33179 and LP339, there is also SA571 and without the scheme and equipment, all this is quite complicated.

WBR
JaMi
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