My latest oops...

[lmrubin]

First my question - All of the ICs should have a +5v and -5v (approx) on the Surf Pi except the 555. The other boards that I made and worked (at first) had negative voltages of about 4.75 roughly. Now they only have about negative 4.2. The positive voltage is a hair over 5v on each. My question is whether or not I should be concerned that the negative voltage is so much closer to -4v now (-4.2v)???


Now my latest screw up - I couldn't get my board to work again and it wasn't driving me absolutely nuts. I was replacing chips left and right, then transistors, resistors, diodes - even the sockets. Couldn't find the problem. And I don't even want to say how much time yesterday I spent trying to fix it (all day). I finally figured out the problem. I had taken a few parts from my other unsuccessful attempts...in this case a few of the resistors that I didn't have new ones to replace. Well, you know how sometimes you have a resistor that's sort of standing up at an angle and not lying horizontal? Well, the leg of the resistor that was tucked under the body of the resistor BROKE right at the board...I never saw the break...a whole day wasted. I feel like quite the moron...although I'm glad that I may be up and running now, if this negative voltage thing isn't a problem....probably is...

[waltr]

Oh, we have all spent much time and effort trying to find a problem like that.
What counts is finding it without giving up.

For most of the detectors -4.2V will work fine.

Do check the data sheets for the op-amps.
Note how close the input and output Voltages can go the the power rails.

[6666]

Broken parts can be a problem, over the years I've fixed a few pcb's for members here, one tricky fault was the bloke had drilled out a VIA and re soldered the hole on both sides , trouble was there was no path from one side to the other, all these things test us