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MidBand QMX, not receive on 20/17/15

  

everything worked, but today there was no receive on 20/17/15 bands. On 60/40/30 bands receive is fine. What could be the reason??
 

I'm thinking of replacing the PCM1804. Because, when pins 5 and 6 are short-circuited, a distorted receive appears.
 

As the PCM1804 is common to all bands and you still have RX on the lower frequencies, it's unlikely that is the problem. This sounds more like an issue with the band switching circuitry.
?
Al, K2ZN
 

On Thu, Aug 15, 2024 at 09:42 PM, Nurlan wrote:
no receive on 20/17/15 bands
Nurlan, these bands are related to BPF0 and 1, both using L401a (24 turns). Please check the solders there, especially the solder to RX_IN (turn "0").
?
73 Ludwig
 

It's very easy to get this coil turned around backwards. I installed it properly on my first QMX-MB, and then installed it backwards on the second unit I built. As Ludwig says, check where L401a and L401b are connected. There is only one hole in the v.4 circuit board, and not enough room to insert 2 wires. L401a has to be tacked to L401b.

gl de va3rr

On Fri, Aug 16, 2024 at 11:07 AM, @Ludwig_DH8WN wrote:

Nurlan, these bands are related to BPF0 and 1, both using L401a (24 turns).
Please check the solders there, especially the solder to RX_IN (turn "0").
 

On Fri, Aug 16, 2024 at 07:49 AM, Al Scanandoah wrote:
As the PCM1804 is common to all bands and you still have RX on the lower frequencies, it's unlikely that is the problem. This sounds more like an issue with the band switching circuitry.
Hello! Does this mean I need to replace IC402?
 

No idea. Have you checked all of the soldering in the L401 region?
 

On Sat, Aug 17, 2024 at 04:58 AM, Al Scanandoah wrote:
Have you checked all of the soldering in the L401 region?
Everything is fine with soldering L401.
?
But why when PCM1804 pins 5 and 6 are short-circuited, a distorted receive appears?
?
?
 

Why would you ever short an input pin (5) to a formatting logic pin (6) ???

JZ KJ4A


On Sat, Aug 17, 2024, 3:20?PM Nurlan via <kz7813=[email protected]> wrote:
On Sat, Aug 17, 2024 at 04:58 AM, Al Scanandoah wrote:
Have you checked all of the soldering in the L401 region?
Everything is fine with soldering L401.
?
But why when PCM1804 pins 5 and 6 are short-circuited, a distorted receive appears?
?
?
 

On Fri, Aug 16, 2024 at 07:49 AM, Al Scanandoah wrote:
As the PCM1804 is common to all bands and you still have RX on the lower frequencies, it's unlikely that is the problem. This sounds more like an issue with the band switching circuitry.
How is the range switching bands? On what chip?
 

RX band switching is accomplished with the microcontroller and IC402. However, as others have noted, the issue is probably assembly-related. Check C401 and C403.
?
Is this a pre-built unit or a kit? What kind of test equipment do you have available?
 

?
I think I found the problem.
?
I disconnected the T401 transformer input from pin 9 IC402.
?
Then I connected the input of transformer T401 to RX_IN through a capacitor. The receiver is working.
?
Probably need to replace IC402
 

Just replaced IC402. Worked.
Many Thanks for all

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