Replace a voltage regulator?

Hello,

I have recently bought my first Shruti-1 kit, and this was one of my first soldering projects (at least, the first consequent one).

I successfully assembled the two boards, but sadly I misplaced the 7805 and 7905 voltage regulators. Seeing my error, I proceeded to desolder them to put them in their right places, but maybe in this process I may have damaged the 7805 : on the lead where I am supposed to have -5V, I only have -1,20V. I guess that’s why the Shruti doesn’t boot…

The thing is, while re-soldering it, I accidentally burned the pad for that lead on the PCB, and now it’s gone ! Plus, some kind of ‘lead’ going to C30 have made it’s way out of the pcb aswell… I guess it’s not making the junction anymore…

So I tought I could buy a new 7805 to see what happens ?

Please let me know if you have any advice ! : -)

Adrien

Hi Arien,
first you could maybe measure continuity between the 7805 and the rest of the circuit. You can check this in the schematics or from the picture of the PCB on the build page. You should restore the burned away traces and pads by using a piece of wire to the connection they should be making. Maybe your 7805 is still alright.

Hi shiftr and thanks for your answer,

I checked the continuity ; it seems that I have the same -1,20V voltage on the C30 positive lead, meaning the continuity’s OK ? But I don’t understand why I don’t have -5V on that lead of the 7805… if I understand well the schematics, all the plus and minus 5V alimentation comes from those two voltage regulators ?

Between what points are you measuring? What are the voltages between ground and the other legs of the 7805? Continuity you have to measure with the Ohm setting or the Diode setting (that usually gives a beep if there is continuity).

I was measuring between ground and lead plus of C30. On the other legs of the 7805 I have 9.27V and 0V. Oh and I didn’t knew for the Diode setting, I tried it and it bleeps between that O leg of the 7805 and the + lead of C30

Could you post a picture of both sides of the board?

Here they are

I’m a bit confused … nothing too bad to see on your boards. But what is that dirt next under C1? is that cap still ok?
Actually you should have +5V on the 7805 and -5V on the 7905. What is the voltage on the -5V points?
And you could put some more solder on the power input. You’re supposed to fill the holes up with solder.

I think that dirt appeared when I accidentally touched the board with the iron. Next to that, C3 has lost one of its pad (under the board) so the solder doesn’t stick to it anymore… I don’t know if that matters !
Also, I broke the leads of C18… I’ll have to replace this cap I think.

And I just filled up the holes of the power input, I still have this weird -1,20V value on 7805…

What specs are your powersupply?

And what is the voltage on the -5 points? Can you check if there is no short between the +5 and -5 rail? Is any of the regulators getting hot?

I’m using a 7,5V 300mA AC/DC supply. I have -5V on all the green points (-5v) and -1,20 on the red (+5V) ones… the regulators does not get hot

http://mutable-instruments.net/static/pcb/shruthi_smr4mkII.png

Check continuity between:

  • the “O” pin the 7805 regulator and a +5V point.
  • The middle pin of the 7805 regulator and a ground point.
  • The “I” pin of the 7805 regulator and pin 8 of IC1.

Continuity checking is not a voltage measurement; and this should be done with the power OFF.

Hello pichenettes,

The continuity is OK between all those points

you have a negative voltage on the positive regulator? (7805 O pin to 7805 middle pin=GND)

Certainly looks like your 7805 is broken. So you can replace that. Maybe you better by two because there might be also another problem causing the negative voltage on the positive rail.

The baby lives again, fixed by TubeOhm .

Greets
Andre’