Wrong filter voltage


I’m at the check step of the power supply. I’m supposed to get +5,0,-5V at various places on the board, but I only obtain something like +4.5, 0, -3.9V.

I double checked the orientation of the components, but I couldn’t see my mistake… Any tips ?



What is the voltage of your power supply?

I have a configurable one, tested 6.5, 9, 12.
I also tried with a non-configurable one, a 12v from my m-audio audiophile, I get the same results.

Which voltage you read at SW0 (the pads for the on/off button or the “bridge” to short it)?

configured with 9V, I read 9 dot something, I have an analog voltmetre…
My voltmetre is configured at 50V (At 10v the needle would reach the limits…)

I had the same issue. This was caused by bad contact at J3 level. Since my DC plug was too big to fit in boards hole, I driled it. and the metal that link the two sides was removed … I was reading 3.3 V at the switch level.
So if you drilled J3, take care of this.

I brought the board to work, but had not time to test it, I’ll do it tomorrow and check what you suggest.
Meanwhile, I remember that when I touch the metal plate of LM 7905 voltage regulator, I get some voltage, but when I touch the other one (LM7805), I get nothing in terms of voltage.

This may give to my kind helpers some cues :wink:


No, this is correct… The metal plate is connected to ground on the LM7805, and to the negative rail on the 7905.

ok, so I obtained -4.99V and 5.60V with a working voltmetre and a working alimentation. Still, this is not correct, what would make such value (5.60) ?

It turns out that it was the 7805. I tried another one, I get the right voltage now.