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QCX+ 7805 problem


Ross Tucker (NS7F)
 

My 7805's output is just 2.2V with 11.8V input. It's also running extremely hot. I'm continuing to look for shorts but I'm not seeing any. Any tips?

Ross, NS7F


Jim Painter
 

Ross, see my thread “No 5 volts”. Had similar problems. I ended up blowing D3 (somehow). Never found any shorts. After that I found 7805 and two 10uf electrolytic bad. Not sure what happen first. Check c37 , c38 and c51. On mine c37 was bad, c38 was good and c51 was bad. If you find you need anything, let me know. I have extras.

Jim....kq3s


On Aug 6, 2020, at 9:35 PM, Ross Tucker (NS7F) <rjtucke@...> wrote:


My 7805's output is just 2.2V with 11.8V input. It's also running extremely hot. I'm continuing to look for shorts but I'm not seeing any. Any tips?

Ross, NS7F


The Crunchbird
 

I am reading about a lot of people who are trying to track down shorts on their boards. The answer is to use a milliohm meter which one can cheaply and easily make oneself. One milliohm probe is held on, say the output of the voltage regulator and the other probe is moved along the power track until the lowest reading is found. This is where the short is or it is the beginning of another track to where it is. If the reading goes up, you have passed the short. . 

Maybe Hans can make up a simple kit to sell those in trouble and keep it stocked on each continent for fast delivery. Such a device is incredibly useful and will be used for a lot more than fixing kits as they are the ultimate form of  continuity tester. Where one is testing the continuity of a circuit to a coil it is possible to see which side of the coil one has the probe on due to being able to read the coils resistance or not. Here are a couple of links to give one an idea although there are numerous others if one does a search on google. Dave. N2SN 






Lionel B
 

Also July/August 2014 QEX milliohm meter project.  I built one. Very handy meter.


The Crunchbird
 

Here is the article for the milliamp meter, Dave. N2SN


Dick de V
 

Ross, I had the same issue. I didn't find a short circuit either.
 After I disconnected D2 on one side the problem was gone and I normally had 5 volts.
In my case C2 turned out to be defective, had internal closure. Check the 100 NF capacitors for closure.

Dick   DL1CLM


Ross Tucker (NS7F)
 

Dick- lifting D2 revealed the problem: a solder bridge UNDER my tcxo board! Now it works!