开云体育

ctrl + shift + ? for shortcuts
© 2025 开云体育
  1. QRPLabs
  2. Topics

Damaged resistor R520

 

Just completed build of the QMX mid bands. While installing T507, I accidently damaged R520 resistor (5.1K). I replaced it with a 4.7K thro hole resistor.
The radio powers up alright with all else working wine including Audio and RF sweeps normal. The SWR sweep however shows 2.6:1 on all bands. I have no doubt this is linked to the 4.7K resistor. Any suggestions on the best way forward. I do not have a 5.1K thro hole resistor. One of the pads has been damaged so an smd replacement is not an option.
Any suggestion is welcome please.
 

Hi,
The value of a QMX R520 is 49R9 Ohm and not 5k1.
You can use two 100R in parallel or 56R and 470R in parallel.
--
73 Bojan S53DZ
 

Hi Rey
?
Looking at the circuit diagram R520 is a 49.9 ohm resistor, replacing this with a 5.1k would certainly affect the SWR readings.
?
You might get away with using a 47 or 51 ohm through hole resistor. If you have a batch of 47 and 51 ohm through hole resistors measure each one and see if you have one at the edge of its tolerance range.
?
Using the intended 49.9 ohm smd component would be ideal...even if you have to repair the PCB trace/pad with wire.
?
Good luck
?
Steve G4EDG?
 

Thanks Bojan and Steve
I have those values. Much appreciated
73
ZL1REY
Rey


On Wed, Sep 25, 2024 at 8:17?PM Steve G4EDG via <g4edg=[email protected]> wrote:
Hi Rey
?
Looking at the circuit diagram R520 is a 49.9 ohm resistor, replacing this with a 5.1k would certainly affect the SWR readings.
?
You might get away with using a 47 or 51 ohm through hole resistor. If you have a batch of 47 and 51 ohm through hole resistors measure each one and see if you have one at the edge of its tolerance range.
?
Using the intended 49.9 ohm smd component would be ideal...even if you have to repair the PCB trace/pad with wire.
?
Good luck
?
Steve G4EDG?

1 - 4 of 4