148gtl NW ST Soundtracker low AM power

[brandon7861]

I think the only difference between your radio and the schematic bayou posted is that yours has nightwatch. In your pic, it didn't look like that was working. Maybe the NW board is toast and pulling down a voltage somewhere. Might have something to do with bright not being so bright too.

 

[dss56]

Brandon

I'll have to look and see if i can unplug the module that is mounted to the side covering the pll area. I guess the nightwatch was a big big failure for these radios.
Why not illuminate the front with leds or some type of fiber optic.

 

[brandon7861]

And while we wait if Bayou can get you a voltage measurement, I went ahead and calculated what it should be based on the schematic he shared.


Edit: so if something (like a bad NW electroluminescent driver) is pulling the 9v down to 5v, the math would come out to 1.4v on the mic jack. Check for 8.4v.

 

[BayouRadioAmplifier]

yes, measured just about 2.2 V from MIC 3 to negative.
when keyed up it goes to ground.
should not mess up the 8.4 V line, or radio would not work.

I keep my display on BRT. when changing to DIM and NOR the meter
lamp does not change much, but the channel LEDs get dimmer.
and no dimming when keying up in AM. so maybe
copy the BRT circuit. there could be a problem in the NW circuit.

 

[dss56]

The reason I asked for the voltage is I use a noise toy box on my cobra 29 and works great for 5 years, I tried on this 148 and will not key up. The pin 3 does not go to ground when keyed. So the sd card box will work with a manual push of a switch but will not key auto pin 3 needs to see ground in the keyup mode.
Well not that important as I posted all my other radios pin 3 goes to ground when keying up the radio.
Tomorrow will dig back in and see if I can remove the nightwatch/disable it even though it does not work.

Thanks again for verifying the mic pins and maybe they changed the way this newer 148 keys.
I thought pin 1 was the ground wire when pin 4 is connected you have receive and when pin 1 and pin 3 are connected you get transmit.
I checked pin 1 in the radio and its not at full ground but radio still works.

Again thanks and back at it tomorrow

 

[dss56]

So i was back at the radio and removed the Night Watch module.
Then had to figure the wires and voltage for the channel display/meter and the LEd for receive and transmit all is good in that department.

Still having problems on the mic on pin 3 im getting 1.4 volts in receive nothing in transmit.
Also if i put the ohm meter from pin 1 to pin 4 i get the short for receive.
I put the ohm meter on pin 1 to pin 3 transmit and i get .453m ohms in transmit I do not get a true short like all other 4 pin radios yet the radio works. I wanted this to work like it should. I checked for those caps c404 and c407 not near the mic connector.

Again might not be the correct schematic the wires from the mic connector go to a small connector soldered to the pc board.
Ill play some more later tonight with the radio and get some pictures.

 

[brandon7861]

Pin 4 goes to ground in receive. This grounds the speaker so the audio comes through during receive. Removing ground during transmit disconnects the speaker so it don't let audio through while you transmit.

Pin 3 goes to ground in TX. A half an ohm isn't bad considering it goes through the mic cable and switch contacts. It uses a different set of switch contacts than pin 4 in receive, so a slightly different reading is not unusual.

You can consider 0.4Ω to ground good enough for your purposes and I don't think it is worth cleaning the PTT switch contacts unless it gets higher or the audio gets scratchy.

This particular radio is not going to give you 8v for your noise toy without modification to both the radio and toy. The easiest approach would be to decouple the mic audio between pin 2 of the socket and L404 with a DC blocking capacitor and send your power down pin 2 like phantom power supplies use. This would require similar changes to the toy.

 

[brandon7861]

With respect to modifying the noise toy, the hard part is powering a device on the same line it sends audio down. Unlike a condenser mic where the mic supply naturally has the audio superimposed on it, the audio chip may not like that.

If the supply to the toy is low impedance, it will short the audio. The hard part is blocking audio while passing DC, since audio is a low frequency.

Without knowing the toy power supply requirements, I cannot calculate the values needed. The resistor value will be whatever value is just high enough that, if placed across the audio line to ground (since the supply cap is essentially doing that), would not kill or distort the mic or toy audio ~ probably around 10k or 20k. The cap would be based on the toy current requirement and how fast you need it to charge from that resistance (how many times you want to send noises in a row).

I think this is quite doable if you don't plan to sit on the toy buttons all day. The only question is how badly do you want the toy on that radio.

 

[dss56]

Brandon.

Here is how the box works.

It has an SD card mp3 player.
I have designed the boards so there is a reverse and forward search buttons on the box.
And also and auto advance when you key the mic a different sound will play every time or you can lock your favorite sound.

The way the keying works and has been since i designed these boards 5 years ago is>

It uses pin 3 and all it needs to activate a relay on the module for a split second to key the box, the box cant have a steady ground just a second/fast pulse for the relay.

I do this this way on the relay 1 side goes to 5v on the board and then the other coil side goes to pin 3 with a 330uf cap and a 10k bleedoff resistor to just see ground for 1 second.
Then the sd card will sound off no matter what mode you are in.
Box also has the 2 manual buttons to activate the sounds.

Been working for 5 years 0n any radio but this 148gtl thats not seeing a true ground when keyed up on pin 3. Also works with any mic adapter 4-5 pin 4-6 pin.
So I know something is still not right but not worried.

you need the ground pluse as the 2 control forward and reverse cant have a long potential ground as they also control the up down volume.
If you hold in the buttons it will lower the outgoing volume to low and back to high so the little circuit i use on the sd modules works great as you can see when I key the box in the video.

have a look

 

[dss56]

Well after screwing around and playing with pin 3 I was able to put a diode on pin 3 inside the radio in series with the wire to pin 3. and now the noise box will work properly as it should.
I want to use this 148 as a test radio because ssb and also its a 4 pin, all boxes are wired for 4 pin radios and have been working for 5 years until this radio.
Here is a video of what i did yo remove the non working Night Watch module.
The brite dim was disabled as not needed and the spot will be used for a channel kit rotary sw soon. At least the radio is working now as it should and thanks to all who chimed in with help and suggestions. view this on my server.