From: QRPLabs@groups.io <QRPLabs@groups.io>
On Behalf Of James Daldry W4JED
Sent: Friday, May 24, 2019 8:12 AM
Subject: [EXT] Re: [QRPLabs] 40M QCX 14.8V on Voltage Regulator Output
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During the 50 years that I was employed in electronic trouble-shooting and repair I had the "pleasure" of following repairs attempted by people that didn't know what they were doing. The results ended in two groups - (1) the units I had to reverse all the
work the neophyte did, then repair the equipment and (2) the units I simply handed back to the customer, with the information that the customer had destroyed the unit.
The fact that you managed to read a negative voltage on a unit that doesn't have a negative power supply means that you don't have the slightest clue about what you are doing. Put the solder pencil away and hand the board, untouched, to someone who knows
what he is doing.
On 5/24/19 3:10 AM, KM6ZMZ wrote:
Hello all. I was really hoping that my first post would be a success story about my QSX build but upon firing it up for the first time today, all I got was a blank backlit screen. I wasn't alarmed
at first since I had been warned that I might need to adjust R47 but when that didn't work I started checking voltages and discovered that I was getting 14.9V on the input to the voltage regulator and -14.8V on the output. I checked pin 3 on the LED and am
also getting -14.7. To clarify, with the positive meter lead on the output pin of the voltage regulator and the negative lead on positive side of the power supply input, I am getting negative 14.7V which I am also getting on LED pin 3 as well as the three
1 pin test points. There is some variation but all of the readings are over 14. I am guessing that this is a nice paper weight at this point and I am already planning on ordering another kit if it is, but I need to figure out what went wrong so that I don't
repeat it. I measured the resistance through the voltage regulator and got: 19.9k-input to ground. 22.9k-input to output. 2.8k-output to ground. I've gone through and checked for bad workmanship and I have searched the forum for similar problems but I
am out of ideas. I plan on replacing the voltage regulator tomorrow and seeing if that does it but I'm guessing that even if that is the problem it is too late for this build. The only thing that gives me a glimmer of hope is that I didn't hear any pops
or smell any smoke. I am using two 2S 7.4V 800mAh LiPo's in series for power. The voltage regulator never got hot or even warm.
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