Fixing a blown SuperPRO

[danlee58]

By the way, I'm using a schematic for an ARMmite PRO, not SuperPRO.

This started off with your saying the SuperPRO was bad, why would you use the ARMmite PRO schematic?

I couldn't find a SuperPRO Schematic!

[danlee58]

I printed out the SuperPRO Schematic, now I need the layout.

[basicchip]

This will get added to the pin diagram page in the Help files

It is the part placement

[danlee58]

i'm going to desolder C15. If that doesn't reduce the current, then I'll try other caps. I don't see any other path for current drain except the LPC1756.

[basicchip]

All the caps on that board are ceramic, and also very unlikely to fail even with reverse polarity. Electrolytic capacitors can fail when reverse biased, but there are none on the SuperPRO.

If th 1756 is dead, it should also be hot, if it's not, that could be good, as one or the other of the voltage regulators is bad, and those are much easier to swap out.

[danlee58]

The 1756 is not warm, but the 5.0 Volt regulator and the 3.3 Volt regulator are both HOT. They don't seem to be bad, just loaded. The output of the 3.3 Volt regulator (u2) measures 1.2 Ohms to ground, and the voltage is 0.3 Volts.

I'll try to lift the output pin of U2, and check again.

[danlee58]

I lifted the output pin of U2. Now nothing gets hot. The output of U1 (78M05) is 4.89 Volts. I can't measure the output of U2, because the pin is gone. I still measure 1.2 Ohms to ground from any 3.3 Volt point on the board.

I think that it's time to order a new SuperPRO board.

[basicchip]

When you measure the resistance to GND did you apply the + side to the 3.3V? Otherwise you might be measuring the parasitic diodes of the chips, when you measure with the + probe on GND you are forward biasing those and the resistance will be quite small.

The next step would be to apply 3.3V to the board and see if the LED lights up, or whether there is still something dragging it down.

[danlee58]

The resistance is the same forward or reverse polaeity. I'll rig up something with 2 AA batteries, thatn should get close to 3.3 Volts.

[danlee58]

I got 3.0 Volts from 2 AA batteries. When I connect to the 3.3 Volt line the Green LED lights, but the battery voltage drops to about 2.3 Volts. I pushed the reset button & switched the LoadC switch with no effect. The 1756 gets hot under these conditions.

Time to replace the board!