external speaker info and solution.

[gartnl]

So I noticed that whenever I connect an external speaker, the audio-amplifier shuts down after a few seconds.
The same happend with a baofeng speaker mike. It happens on both QS 5R's.
This got me thinking: what if the amp is meant for high impedance earplugs with DC connected output?
So I placed a 100 uF capacitor in the line and behold: sound!
Did QS really save on an output capacitor ??

[egzumer]

I have no idea how that works, however a friend reported that his earplug speaker gets hot while it is plugged in, looks like there is some DC voltage not filtered out. It is also worth noting that there are different board versions, most common are older 1.4 and newest 1.6. The newest one has some speaker-mic issues fixed (EDIT: this is not true, read more below), mainly PTT not working while receiving incoming signal, maybe the issue you mention is fixed too.

[egzumer]

Actually this is something they broke in v1.6. There is a 3.6V DC voltage at the speaker pins, this is not the case with v1.4

[gartnl]

Strange, my speakemike isn't working. Even with the capacitor mod. The sound is there now, but no TX with the speakermike. Not even when on the other VFO. Well, they are cheap so can't complain too much.

[egzumer]

They messed that up, they used wrong, double ended audio aplifier, now they have problems, baofeng for instance uses single ended one. They fixed the PTT problem but now there is this DC component.

[OE1MWW]

yes, can confirm. UV-K5(8) on the speaker output (tip of 2.5mm) are ~3,8 volt, on the UV-K5R was no voltage at that pin.
There is a mod info floating around: the wire from speaker to ground inside the mic should be replaced by a 47uF capacitor.
Works, no difference in sound quality

[ErikS-web]

What speaker ? Intern radio, or externally in microphone ?

[egzumer]

This is caused by a short in the radio. Now when removed the PTT doesn't work correctly again.

[ErikS-web]

When I plug in my external microfone, the TX/Red-light is on for a split second (rev 1.6 board).

Any photo on adding an elco internally. There is not much space direct at soldering point of speaker,

[gartnl]

How strange. They solved a problem with a short, a blob of solder in fact?

[egzumer]

This is not a fix. The cure is worse then the disease. This is an accident that it fixes anything. The speaker-mic socket is hand soldered, and contacts where the blob is are extremly close.

[OE1MWW]

[ErikS-web]

So the modification in in externally speaker/microphone. Not intern the Radio ?

[OE1MWW]

yes, it's done in the external mic.

[gartnl]

Ah. So others came to the same conclusion. I used it in a communications speaker and in the external mike. The C does not hinder other sets from beeing used.

[ErikS-web]

Clear picture #thumpsup

[ErikS-web]

On SP+ I measured on my radio 3.6 volts (UV-K5(8) rev 1.6).

With 47uF I was not satisfied with the sound on low-frequenties, so I placed 100uF in the microphone (type Baofeng K-780MIC).

I used an NC strip as new soldering pad for the black wire, from where the elco is positioned to the original connection (GND)

Now you can also see that the PTT2 is not connected. I you wish to have it, all it needs is a soldering connecting to PTT

[ErikS-web]

That external PTT was not working while receiving incoming signal, I had on my old rev 1,4 board.
And I thought they fixed that with 1.6... with bad soldering ?

I mentioned the difference in PTT on the wiki

[egzumer]

There is a unpopulated place for capacitor, this capacitor fixes the issue with external PTT not working when speaker is playing sound. This is the same fix as a capacitor in speaker-mic.

Before, the path between pads has to be cut:

After:

[bsdinis1]

Wouldn't it flow through the speaker itself?
If you remove the DC offset from only one of the outputs, there will be a 4V difference between the two speaker output terminals, the internal speaker would act as a 16Ω resistor.

[egzumer]

No, it wouldn't. Capacitor doesn't remove offset, and DC can't flow through capacitor, so how would it flow through 16Ω speaker?

[FrancoisDeveraux]

Thank you sincerely for your help in everything here. My question: In the two photos (before, after) with the addition of the 47uF Capacitor, is it correct that there is a trace from the "-" to the "+" solder pads which must first be cut (scraped or otherwise disconnected)? I think I see it in the photo (before pic) but I am asking to be certain. My understanding is the capacitor is tantalum; must it be tantalum or would any 47uF that fits there work?

[egzumer]

Yes it has to be cut, otherwise it would just short the capacitor and it would have no effect whatsoever. I don't know if there is any other type of capcitor that would fit there, but I don't see a reason why it has to strictly be the tantalum type. I guess ceramic would be just fine too, although I don't know if there are ones with 47u or more capacity.

[ag6ju]

Hi my name is NIKO , AG6JU, I worked for com-spec.com Communications Specialists in Orange California. owner of com-spec.com want to hire you to write specialized UV-K5 firmware for him, please contact me , if you are interested. [email protected]

[gartnl]

Sometimes topics like this lead to a surprising discovery!
After putting the C in the speakermike TX would still not work, but sound was ok. But my UV-B5 wouldn't transmit either anymore. Turned out that in the mike the wires from the tip and sleeve of the 2.5 mm jack were reversed.
Without the C the PTT would find a dc-path through the speaker, but with the C that path was blocked. Changing the wires solved it for both the UV-B5 and UV-5R. As a bonus the mike signal improved, because that signal also used to go through the speaker.
So much for el-cheapo mikes from the far-east ..

[bsdinis1]

I bought a cheap (<$2) speaker/mic from aliexpress and the speaker died after just a few minutes of use, I think it was 8Ω. It sounded very muffled, and it was super quiet even at max volume and the red LED would also light up when there was sound coming out of the external speaker, the louder the sound was the brighter the LED would flicker in-sync with the sound.
I salvaged a similar looking 32Ω speaker from an old PMR446 radio, soldered two 100µF aluminum capacitors in series back to back to form a 50µF bipolar capacitor and then soldered one end to the speaker output cable and the other end to the PCB's speaker input pad, this way the headphone jack is also protected from DC.
My radio puts out about 3.97V DC from the speaker output (tip of 2,5mm jack), now it measures 0V DC after the capacitor(s).
I also removed the stupid red LED, the anode was soldered to the microphone input pin and the cathode was soldered to the PTT pin. (3rd picture)
Now it works fine, the speaker sounds very good and loud and the external PTT works while there is sound coming through the external speaker.

[bsdinis1]

I haven't opened my radio yet, but it's probably a v1.6
I wasn't able to pry the radio open with a credit card, I really don't want to jam a screw driver in there and dent the plastic casing, does anyone know what can I use to open the radio without denting it?

[egzumer]

The best tool is a wide flathead screwdriver :)

[ErikS-web]

Have a look at YouTube open case uvk5

[bsdinis1]

I finally got a set of prying tools and was able to open my K5(8) without denting it, the PCB is v1.6

There was no solder blob on my radio

Those two points measure 47Ω

The 2,5mm jack is shorted to the other side of the capacitor