On 11/10/2021 12:05, EA4B wrote:
I have been completing several stages with satisfaction according to the instructions on the website wb5rvz.org. Last week I finally had the possibility to start the receiver when I reached the RX_OpAmps part.
With great surprise and satisfaction, I verified how well it worked in the bands that I have selected for its construction: 17m-20m-30m, with great reception also in 15 m, 40 and 80 m, even in the om broadcasting band.
A few days ago I decided to continue and I have completed TX_OpAmp and there I am having problems.
the values ??being much lower than expected, the two circuits U6 and U7, give exactly the same measurement sequence voltage on its pins:
From PIN 1 to PIN 3 it should be 2.5v and the measurement I get is 1.75v
PIN 4 is the only correct 0v (ground)
From PIN 5 to PIN 7 it should be 2.5v and the measurement I get 1.72v, 1.75v and 1.76v respectively
Pin 8 should be 5v and the measurement I get 3.52v
I have gone through the entire assembly without success to find out if there was any confusion in the resistor values ??or any short or ground fault.
In the end - big mistake - I estimated that it could be a failure of the voltage regulator of the power supply, so I replaced the voltage regulator TL78L05 (U9 in the Softrock diagram), without any result. This was not the problem.
I decided to check how the inputs and outputs of the 7805 voltage regulator behave and I find this surprise:
? With the 7805 output pin in the air, without soldering on the board, I measure: PIN 1 (input) 12.3v and PIN 3 (output) 5.5v
? With the circuit connected on the board in place: PIN1 (input) 5.1v and PIN 3 (output) 3.5v
CONCLUSION: The source voltage drops when the 7805 regulator circuit comes into play.
José María,
The voltage data that had to be obtained when measuring the voltage
of ICs U6 and U7 (double operational TLV2462CD) does not correspond to what was expected,
These voltages are fixed by the R21/R22 divider but as you found the 5 volts is low on pin 8.
The 7805 heatsink gets very hot, plus the Dividers Stage components
get hot too, including the U5 divider IC (74AC74 Dual D FF). As a result the softrock rxtx receiver has stopped working and I don't know how to solve the problem.
You need to find out what is loading the regulator.
I do not think any of the ICs should get particularly hot. Use an eyeglass (Loupe) check all your soldering, maybe a solder splash or whisker.
Carefully lifting pin 8 with a pin or needle might show a bad IC but an error is the most likely fault.
73 Alan G4ZFQ
73 Alan G4ZFQ
