bitx20 3C SBL - Bandpass filter inductor issue


Pirok-W4UNX
 

I've got this kit I've had around for 4 years and it is mostly working though there is an issue with the three inductors not "adjusting." The tuning plugs move just fine, but I have to put an absurd amount of pressure on them, then they start to pass RF. I've actually picked up stations after fussing with them, but I would like to know if anyone else had a similar issue with the bandpass filter and any guidance to correcting the lack of tunability.

Thanks!
--
Jason Pirok
W4UNX


 

Hi Jason,

What capacitors do you have in the filter?  It is suggested to use the 33pF value as higher values might not give enough range on the inductors.

When the filter is adjusted correctly, normally the cores will be up near the top of the shield can -- not near the bottom.

Did they go into the boards OK?  Sometimes the pins get pushed into the forms when the inductors are pushed into the board.  If that happens, the thin winding wires may break off the pins.

73,


Mark


Pirok-W4UNX
 

I believe the pins went in okay (it was close to 4 years ago now that I started this project) but that is worth exploring. Just to be triply sure, I removed all solder off the cans/leads one at a time and reflowed them all. Now, as I sit here typing this, the fact that pressing on the cans and wiggling them changes the behavior, I may need to just take them apart and check out the internal connections. No sense putting it back in the case and taking it out if there is a bigger issue.

Thank you Mark! A big thank you to Sunil as well!
Your assistance is greatly appreciated!

Jason Pirok

On Wed, Jan 13, 2021 at 10:57 AM Mark - N7EKU <n7eku@...> wrote:
Hi Jason,

What capacitors do you have in the filter?  It is suggested to use the 33pF value as higher values might not give enough range on the inductors.

When the filter is adjusted correctly, normally the cores will be up near the top of the shield can -- not near the bottom.

Did they go into the boards OK?  Sometimes the pins get pushed into the forms when the inductors are pushed into the board.  If that happens, the thin winding wires may break off the pins.

73,


Mark



--
Jason Pirok
W4UNX


Curt
 

Jason

I suggest a little more evaluation before removing the cans, to minimize damage. Did you check the capacitor values?  can you gently raise the inductor core to the top, maybe observing receive signal noise while you do it? Best to affirm its bad before trying to unsolder it.

Curt


 

Hi again,

It's usually pretty easy to tell if a pin got pushed in.  As long as the shield cans are all sitting flat against the PCB, then the pins on the other side should all be at the same level.  If any are shorter, it likely means those that are got pushed in.

It is possible to de-solder just the shield can tabs, and then pull the cans off from the top.  Just be careful as some have plastic side bits that come off with the can (be sure to observe their position so you can put them back the same way).

73,   Mark


Lawrence Galea
 

Check the pcb for a hairline crack


On Wed, Jan 13, 2021 at 10:13 PM Mark - N7EKU <n7eku@...> wrote:
Hi again,

It's usually pretty easy to tell if a pin got pushed in.  As long as the shield cans are all sitting flat against the PCB, then the pins on the other side should all be at the same level.  If any are shorter, it likely means those that are got pushed in.

It is possible to de-solder just the shield can tabs, and then pull the cans off from the top.  Just be careful as some have plastic side bits that come off with the can (be sure to observe their position so you can put them back the same way).

73,   Mark


Pirok-W4UNX
 

Thanks to everyone that helped with this! I found a pad that had cracked and pulled off the PCB at some point. Everything is good to go!

Again, I appreciate all who gave me suggestions!

W4UNX