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.
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