Hi Dohn, I think you probably accidentally posted this to the wrong group, the SoftRock40 one is the more obvious choice.
I have just printed out a set of circuits for the v6.3 TX/RX as I have not actually built one to take a look. >From the symptoms, I am surprised that the 12v supply current is not excessive >now. For the output of the 5v regulator U4 to be so low and getting hot, >suggests a short circuit and lots of current, or very near on the output of >it. The low 3v3 rail is low because the 5v feeding it is not there, or it >could be dragging it down. You need to isolate the output of U4, and see whats pulling it down. I do not know what is in Robby's notes, as I never bother with them, but if you have only built the LO section, the 5v from U4 only goes to U5, the 3v3 regulator and a couple of capacitors (which I guess were fitted in the previous section anyway). If the initial power supply tests were ok before building the LO section and the 5v / 3v3 rails were ok, I guess you have a solder splash or short circuit on either of the rails, most likely on the Si570 from the 3v3 supply to the case. All I can suggest is unplug U6, if you have that fitted, then remove U5 from the board. Check if the 5v returns ok, if not then the problem is on the 5v rail. If the 5v is ok, then problem is U5 or afterwards on the 3v3 rail. Just a process of elimination to go back to your last known working state. 73, Bob G8VOI --- In [email protected], "n8ewy" <n8...@...> wrote: > > I'm stumped. I just finished the LO section. After the first section (power > supply) All was well. 3.3v and 5v were solid. Current draw perfect. > > Current draw with resistor in LO section was right on. HOWEVER now I can > only measure .7v at 3.3 rail and U4 becomes VERY! hot. Further, voltage at > U5 measures 5v coming in on the two outer pins on input side and .7v on both > pins on output side. (go figure) > > All switches on SW1 set to 0. U6 in properly. SI570 appears to be soldered > perfectly under scope. No visible solder bridges top and bottom. > > What the heck???? > > Dohn N8EWY >
