Finally, finally, she/he/it arrived while I am still in Wien (OE1)!
It was a little adventure but now I am in the select circle of Lab599 TX-500 MP owners!
I have it for just a few days but, man, oh, what a nice radio is here!
And with a spare BP-550 battery pack.
On the G90 Groups is an interesting discussion about an audio feedback (squawk) at high volume.
The subject is now locked but I think it will be a good added value to point to the source and the solution.
As I wrote there, the problem is most probably due to the MLCC capturing audio and producing a feedback via the PCB.
It is a known phenomenon that cheap MLCC act like condenser microphones.
Today, I opened for the last time my G90 to put back the LDOs as the small SMPS put some spurious into 20m band and this radio will be put on sold.
I did some photos on the front end bandpass filters (see this post) for future reference and I get back to a small soft plastic cylinder placed on the shield above the filters.
Yup, this is precisely what I reccomended to reduce that squeal, a simple damper to reduce the vibration between the upper case that hold the speaker...
It will be interesting to check if those radios that exhibit the audio feedback have that little plastic damper.
If not, I think it would be easy to add something similar or a little piece of foam.
Baofeng DM-32 desktop "charger" isn't a proper charger but a desktop stand with a charging indicator.
The charging circuit is built into the battery and powered by a 5V/1A power supply.
Inside the desktop stand is a detection circuit that change the colour of a dual-colour LED based on a LM358 dual op-amp configured as a comparator.
Here is the schematic:
