POwer test of 4Pole Mission

The hole on the header marked GND.

Smartass! Good point ‘though! Following Titus’ suggestion, I get the same results, 0 on one side of the diode and .4 on the other.

Didn’t mean to be a smartass. It took me a while to realize that once the board is powered, all the voltage and ground points are active/connected by the PCB traces. I mean this is really a “duh” moment, but it wasn’t obvious to me from the start.

It’s okay to be a smartass when you’re right. I appreciated the advice, just giving you a bit of a hard time, hope you don’t mind. I’m wondering if I’ve screwed up D1?

I think maybe. You should definitely have voltage on the other side of it. ~9V I think…

I’m still studying this stuff, but I believe the stuff near the regulators steps the voltage down to 5 and then splits it into -/+.

This is strange, one side of the diode should be at the same voltage as your power supply…

A protection diode prevents the wrong polarity voltage from going through it and damaging the circuits behind it right? So what happens if the diode burns out? Does it stop passing voltage or pass inconsistent voltages?

The power supply flow is the following:

  • Arrives at the connector.
  • The circuit is eventually opened / closed by a switch if you solder it at the SW switch (it’s kept close if you solder a jumper here).
  • When the polarity is wrong, D1 blocks the current. Otherwise it just causes a small voltage drop (a few tenths of volt) across it.
  • Then the input voltage is sent to the LT1054 and the few caps around it - and a negative voltage is generated from it (if the input is 10V, the output, on pin 5 of the LT1054 will be -10V).
  • The the 7805 (7905), brings the 10V (-10V) to 5V (5V). Excess power (input voltage 5V times consumed current) is dissipated as heat.

The diode doesn’t burn out unless you apply very high voltages to it. If you plug the power supply with the wrong polarity it’ll just block the current, but it won’t be damaged…

Thanks pichenettes!

I see what you mean. One side should always be input voltage. Has to be. This points to a problem upstream then, to SW, the connector, or the PSU. Right?

Is there supposed to be a bridge across the two SW points if there is no switch? It’s a rhetorical question. I’ll be slamming my head in a door for the next few minutes. I had taken out the diode, just for fun, and just dropped it on the floor and of course it disappeared. Argh!

Yes, there must be a bridge across the two SW points.

My first Shruthi has a power switch so I forgot about the bridge. I’m getting readings of +8 and -8 at the various points. This is using the same power supply (rated at 9V) that I’m using for the first Shruthi.

Thanks for putting up with me.

Which points are you referring to? Those around the diode and LT1054 we were discussing lately or those shown in the assembly instructions?

In the assembly instructions. After I put the bridge in, things suddenly started working, although the voltages are high.

Could you please measure the voltages at the I / O / () pins of the 7805 and I / O / () pins of the 7905

7805 0 = 7.5, - = 0, I = 12.5 7905 0 = -7.1, I = -12.2, + = 0

This is weird! Is your meter set to DC mode or AC mode?

DC. Now you’re starting to worry me. Fairly soon, I’m going to ship the board to you and maybe you can figure out what I’ve done wrong.