Unbricking a Pair of ATS25 Receivers

Back in January I was approached by a member in one of my ham radio clubs that wanted some assistance with a pair of ~$100 ESP32 microcontroller-based shortwave radios he picked up on Amazon.  He passed them over to me and after initial inspections I was rather confused.  I managed to learn how to update the firmware they run (using Arduino IDE), and was able to flash all sorts of software versions, but I was never able to get them to boot up.  They would hang on the message "Si473X addr: 63." I asked in an online forum about the issue but got no replies.  At this point, the best I could figure is that there was a hardware failure of some sort, either with the ESP32 controllers that run the radios or the Si4732 chips that live at the heart of the radio.

I reported back to the owner that I was suspecting a hardware failure, but I had no way of knowing exactly what part it was without being able to swap a couple things with a working one.  He decided he would cut his losses and move on.

Fast forward a couple weeks and I needed to put in a Mouser order for another project and have a few extra dollars in spending cash, so I ordered a pair of ESP32 boards and a pair of Si4732 chips to experiment. I started with the easier part to replace - the Si4732 and after using my hot air gun to remove the old one, cleaning the pads, and hand-soldering in a replacement, I turned on the first one and it booted right up! I repeated the process for the second one and fixed the both.  This was my first ever successful surface-mount IC replacement attempt.

I reported back to the owner what I managed to do and worked out a trade so one goes back to him, I keep the other one.  It was at this point that I found out that he (at separate times) had these on a coax switch to share one antenna between several radios and was running an HF amplifier thru the switch.  Looks like the RF leakage in the switch fried the chips in the ATS25 receivers.

Hopefully this post will be useful to someone that runs into the freezing on the "Si473X addr: 63" message.

73 everyone.

Realistic HTX-100 Blinking 28.000 - Fixed!

I picked up a broken Realistic HTX-100 at a hamfest for cheap a while back and wanted to share what I found for the repairs.  The symptom I had was when powering it on, it would just blink 28.000MHz and none of the controls seemed to do anything.  I did some searching around and based on text searches only found old posts saying to send it in somewhere for repairs.  Obviously, these have been long since out of production so that is not a likely repair. My initial guess was a PLL unlock due to bad caps on the PLL board, but that guess was wrong.  I stumbled across a YouTube video about a failed repair of one that had a very similar symptom.  The person that made the video was not able to conclusively determine the fault as the radio started working more or less on its own, but he mentioned finding a metal fragment that fell out of the front switches and noted that if the PTT is held down when the radio is powered on, it will blink the last frequency it is set to and act like it is locked up.

This was as good of a starting point as any for me, so I set out tracing the PTT circuit and found that if there is no 8v going to the front display board it will invoke the PTT line. Long story short, I found a vaporized trace by the 8v regulator and a shorted capacitor (capacitor pictured below).  When the capacitor shorted, the PCB trace burned up like a fuse and took out the 13.8v supply that goes to the 8v regulator. This was capacitor C163 on my rig, but there are others that could short and cause a similar issue as well.

When trying to tack down where the shorted component was, I found it useful to use the PCB jumpers as "divide and conquer" points.  I would pick one, de-solder one side and see which side of it the short was.  Otherwise, you just end up scratching your head wondering which component in that part of the circuit could be shorted.

I'm sorry for not taking detailed pics as I went along, but I hope that someone may be able to find this useful in case they have the same symptom on their HTX-100.