Why Do My Discriminator Taps Always Stop Working Eventually?

[CanesFan95]

Unfortunately, it still doesn't work. I get no audio out the computer speakers, no decode, nothing. The volt meter shows 1.116 volts at the tap point and ground. At the other ends of the wires, I get the same 1.116 volts. But then putting the + lead after the capacitor and before the resister, nothing. - 0 -

When I connect the USB sound card, the voltage drops from 1.116 to about 300 mV. I tried plugging in an external speaker and that made it drop to around 250 mV and no audio. So basically, nothing works. And is it just me, or is it just really hard to tighten a ground screw with a wire under it without the wire keep moving out and not staying under the screw head. I've always hated that.

 

[CanesFan95]

So I scrapped the re-do and just chucked it in the trash and tried one last thing. No components. Just gimme a direct connection and gimme something, anything, I can decode, to see if this scanner even works. Well, that also failed too. So I'm about done and very p*ssed off. Two hours of time for nothing. Very frustrating. I can't imagine what it is that I do with these mods that works great at first but then quits working after a couple years. On all 3 scanners.

 

[prcguy]

The disc_out pad is surrounded by a ground plane. Looks like the wire soldered to the disc_out pad could be touching the ground plane in spots. You can check that with an ohmmeter.

Unfortunately, it still doesn't work. I get no audio out the computer speakers, no decode, nothing. The volt meter shows 1.116 volts at the tap point and ground. At the other ends of the wires, I get the same 1.116 volts. But then putting the + lead after the capacitor and before the resister, nothing. - 0 -

When I connect the USB sound card, the voltage drops from 1.116 to about 300 mV. I tried plugging in an external speaker and that made it drop to around 250 mV and no audio. So basically, nothing works. And is it just me, or is it just really hard to tighten a ground screw with a wire under it without the wire keep moving out and not staying under the screw head. I've always hated that.

 

[CanesFan95]

Ground plane as in touching something else it shouldn't? With the ohm meter, where should I touch the leads and what to look for? Thanks.

 

[a417]

put a ring terminal on that ground lead and the ground screw will snug in better and not be an impending point of failure.

 

[prcguy]

Check resistance from the red wire soldered to the board to ground. If nothing is plugged into your new jack with the red wire it should be a high resistance, don't know exactly what but probably over 1k ohms. If your red wire is shorting to the ground plane you will see an ohm or less.

Ground plane as in touching something else it shouldn't? With the ohm meter, where should I touch the leads and what to look for? Thanks.

 

[majoco]

...and you don't need to use a great big fat cable that could carry 10amps or more - just a skinny one will be good and you don't need so much heat to make the joint. I use wires that I strip out of the old 25-way printer leads - see my pic in post 34.

 

[MUTNAV]

Unfortunately, it still doesn't work. I get no audio out the computer speakers, no decode, nothing. The volt meter shows 1.116 volts at the tap point and ground. At the other ends of the wires, I get the same 1.116 volts. But then putting the + lead after the capacitor and before the resister, nothing. - 0 -

When I connect the USB sound card, the voltage drops from 1.116 to about 300 mV. I tried plugging in an external speaker and that made it drop to around 250 mV and no audio. So basically, nothing works. And is it just me, or is it just really hard to tighten a ground screw with a wire under it without the wire keep moving out and not staying under the screw head. I've always hated that.

If you put the wire on the other way, when you tighten the screw it should help.

Thanks
Joel

 

[Ubbe]

What scanner is that? I believe that the SC and SP are DC signals for fast and slow squelch and have no audio? Are you sure that SC_OUT are the correct place for a discriminator tap?

/Ubbe

 

[Arkmood]

Looks like a 996P2 board and DI is covered...

 

[CanesFan95]

Yes, it's a BCD996P2 and that point is labeled DISC_OUT. That's the original tap point I used 3-4 years ago that worked fine.

 

[CanesFan95]

Check resistance from the red wire soldered to the board to ground. If nothing is plugged into your new jack with the red wire it should be a high resistance, don't know exactly what but probably over 1k ohms. If your red wire is shorting to the ground plane you will see an ohm or less.

Went ahead and tried that. I get no reading on the ohm meter. Not zero, just no reading at all, on either end of the red wire. I poked around with the red lead at other random points on the board and got actual readings of 0.000. So I went ahead and unsoldered the red wire, removed the black wire, removed the mono jack, and basically just took it all out. Then tried it again on DISC_OUT and got the same thing, no reading. But I still get 1.116 volts.

 

[prcguy]

At this point I would stick an oscilloscope on the disc_out and see if there is any recovered audio or data there.

Went ahead and tried that. I get no reading on the ohm meter. Not zero, just no reading at all, on either end of the red wire. I poked around with the red lead at other random points on the board and got actual readings of 0.000. So I went ahead and unsoldered the red wire, removed the black wire, removed the mono jack, and basically just took it all out. Then tried it again on DISC_OUT and got the same thing, no reading. But I still get 1.116 volts.

 

[CanesFan95]

Understood, well I don't have an oscilliscope, so I'm basically calling it a loss at this point. It's done. My only uneducated guess is maybe the first time I soldered to DISC_OUT 4 years ago, I soldered it too fat and shorted it to something else on the board and maybe that slowly toasted something and it finally stopped working. What a bummer. I miss searching around with the tap and finding new stuff. That's like the best part of this hobby.

 

[jonwienke]

More likely you broke the trace connecting the pad to the rest of the radio, and now it's not connected to anything anymore.

 

[manross]

It's never too late to start learning.......

.... here I am with my Dad with a gummint surplus radio about 1956.....

View attachment 89442

Martin that is a great picture!!! Good name by the way. Marty