Shure vintage wireless guitar, died ?

[ricci]

ricci , what number is actually printed on U3 in the reciever?



U101 in transmitter is same part number but drawn completely different (in 2 parts, pg.28 of T1 schems).

https://ibb.co/0qZmLj7

they use the same chip T transmitter
R Reicever

[ricci]

I used the replaced C129 the first time and now U3 and U109 are the same again

https://ibb.co/Q6WLrND (pin 3 - U3)
https://ibb.co/zh313bb (pin1 - U109)

After having welded the first C129 I immediately found these values, once I placed the probe badly and the values were different as yesterday, so this is the probable reason

[ricci]

Here describes how it works NE571

https://tinyurl.com/2p925ky2

[g1]

Ok, there are just some errors in the receiver schematic for U3 then. Some wrong pin numbers and some connections shown that should not be there. (ex. pin 8 vs pin 7; pin 10 connected to 5V)
It would be nice if they had drawn it up like they did for the transmitter schematic.

[ricci]

Ok, there are just some errors in the receiver schematic for U3 then. Some wrong pin numbers and some connections shown that should not be there. (ex. pin 8 vs pin 7; pin 10 connected to 5V) It would be nice if they had drawn it up like they did for the transmitter schematic.

The schematic of my receiver is that of pag. 31 with the U107 chip, only this U107 chip is missing from the layout on pages 26-27

https://ibb.co/QCDfwWw


The first three pins of U3 are connected respectively to:

U3_pin 1 ----> u107_pin 14

U3_pin 2 ----> R142 --->C127--->U109_pin 1

U3_pin 3 ----> C129 ---> U109_pin 1

[ricci]

U3 pin 3 and U109A pin 1 signals look good but your signal levels seem to keep changing. Maybe caused by your "intermittent" problem?

Check the other tantalums like C123, C132..

So all the polarized caps that look like aluminum are tantalum?


Regarding the C123, I had asked Shure Brothers and they replied like this

"According to our documents for this legacy product C123 is not placed on the PCB but has been left off in production."


I have directly replaced C132 and this is the result on pin 7 of U109

https://ibb.co/RbzPPCJ


Distortion has been significantly reduced, even audio, but the volume is 1/10 of that with the direct cable, however if I increase the gain, the distortion is immediately present, little headroom.

[ricci]

I suspect having kept it all in a corner inside a bag in contact with a radiator for a long time, could the heat over time have dried all the electrolytic caps ?

[Helmholtz]

So all the polarized caps that look like aluminum are tantalum?

Don't know what you have in there, but the manual states "polarized capacitors are tantalum types" (page 21).
But maybe they mean SMD types only.

Tantalum caps don't dry out but can fail shorted.

[ricci]

C132 was 100 pF instead of 1 uF, at a great loss, now I have also replaced C127 and finally I have recovered the volume and the red peak led has also turned on. To turn it off I reduced the gain of the R125 transmitter to 1.6 k that is almost to the minimum, I remembered that I did not keep it so low but the user manual comforted me because the factory setting was just like that, pot all anticlockwise, after so many years I did not remember anymore , sorry.

Now everything seems okay except for a very slight distortion when I hit hard on the string, almost imperceptible but there is. Any other capacitors ?

https://ibb.co/LNxTFf3 (input on jack)
https://ibb.co/nRPQGb5 (U3 - pin 3)
https://ibb.co/Hd7bpY1 (U109A - pin 7)

[Helmholtz]

Any other capacitors ?

Maybe C116.
In principle all caps of the same type as C132 as suspect.

[ricci]

Maybe C116.
In principle all caps of the same type as C132 as suspect.

Replaced that too and a little better for sure, my ear is quite sensitive after so many years of playing music and if I do strumming, sometimes I feel an imperceptible distortion that decays even very soon.

[ricci]

For completeness, replaced also C156 and C141 and now the audio is back to normal

https://ibb.co/LZFmNWG (input_before_C156)

https://ibb.co/mz1YndX (C109-pin-1_before_C156)
https://ibb.co/Zmsbq99 (C109-pin-1_after_C156-C141)

https://ibb.co/zf2KVMH (C109-pin-7_before_C156)
https://ibb.co/4TYR7r3 (C109-pin-7_after_C156-C141)

[ricci]

Don't know what you have in there

There are 19 electrolytic capacitors, of which 14 like the ones I replaced, of this type

https://ibb.co/BqB2H8r

and 5 radials

[ricci]

Despite everything well, it seems that the output signal is slightly weaker than the input signal even if they look the same when listening.

https://ibb.co/q1dfj5c

[ricci]

Dear friends, the nightmare returns. I would like to give this wireless to a friend as a gift but after various tests without problems, yesterday I turned on the transmitter, the two diversity leds on the receiver light up but there is no audio from the amp BUT a hum from the antenna https://sndup.net/d8r8/

that does not change with the volume of the amplifier but is sensitive to movement of the transmitter, very loud when the transmitter gets close to the amplifier.

I did some checks to follow the audio signal with an oscilloscope but I don't understand why the signal is present at the input of C107 and it is no longer at the output. I measured the capacity and the value corresponds to the exact one.

Thx


Edit:

My mistake, sorry, i could not suspect but it is my amp that generates noise.