Radio Interference with my PCB

JohnnyFever

Mr. Big's Thug
Joined
Jun 25, 2005
Posts
195
Hello!

So I was checking out my PCBs after being in storage for the past month during a recent move, and when I hooked up by Double Dragon PCB I didn't get sound. I adjusted the volume on my cab (Blast City) with no success. I then adjusted the volume knob on the board itself, and I began to get a radio station! The signal became stronger if I tapped the capacitors near the volume knob on the board. Does anybody know why this is happening? How can I get my sound back? Thanks for the help!

John
 

gusmoney

Unsure if You Asked, For a custom Rank, But Hell,
10 Year Member
Joined
Nov 3, 2014
Posts
1,851
Did you pick-up WKRP in Cincinnati? If so, I might know why.
 

JohnnyFever

Mr. Big's Thug
Joined
Jun 25, 2005
Posts
195
Good one, Gus. Nah. It was some financial talk show. I'm guessing Clark Howard or Dave Ramsey. Not sure. Maybe it was some crazy waves from the future and I should have listened for some stock tips.
 

JohnnyFever

Mr. Big's Thug
Joined
Jun 25, 2005
Posts
195
What would help with the shielding? I don't want to overheat the board. Also, would running fan generate the unstable air?
 

Chaotic Mind

New Challenger
Joined
Jul 9, 2017
Posts
58
There are a couple of possible solutions. First off if tapping the caps makes the radio noise worse than that is a sure sign of bad capacitors. Bad caps is usually the first sign of trouble on most older electronics. I would start with replacing all the caps in the audio circuitry and perhaps the whole bard just to be safe. If that does not fix it then there is a chance the audio amp itself is messed up and should either be replaced or straight up deleted if you do not mind adding amplification externally for the line level signal that results from removing the amp. Will have to do some wire bypassing to get the signal passed on if you bypass the amp. You could try pulling the line level audio before it hits the amp circuit to see if it has noise there. That will tell you where the problem is. Disconnect the amp from the input source signal and check the source signal via external amp. If you still get radio noise then there is a serious issue elsewhere. However if the noise is gone then that tells there is a problem with the amp circuit and my first 2 suggestions should be tried with the cap replacement one first.

These are what I know and both are quite cheap to try.
 

Westcb

Give an Azn, A Break Here!,
Joined
May 17, 2012
Posts
1,190
Hello!

So I was checking out my PCBs after being in storage for the past month during a recent move, and when I hooked up by Double Dragon PCB I didn't get sound. I adjusted the volume on my cab (Blast City) with no success. I then adjusted the volume knob on the board itself, and I began to get a radio station! The signal became stronger if I tapped the capacitors near the volume knob on the board. Does anybody know why this is happening? How can I get my sound back? Thanks for the help!

John

Did you use to play double dragon on your blast? If I remember right DD needs -5v for sound, and the blast PSU does not have -5v on it, unless you have wired in a negatron you will get no sound regardless.
 
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