Touch pHAT, lights up but crashes the pi

I’m trying to use a touch pHAT on PiZero 1.3 . I have other Pis around and it didn’t work on those either.

Symptoms are that when the pHAT is plugged in and I apply power, all the lights come on but the pi does not boot. Remove the pHAT and apply power, and pi boots fine.

Further investigation

  1. The top (logo / no chips) side of the PCB gets hot to the touch, where the two 4x resistor banks are on the other side
  2. If I remove the pHAT and let the pi boot, then add the pHAT, the power consumption (from a laptop USB2 port, as measured by a Startech USBAUBSCHM) jumps from 80~180mA to just over 500mA and then settles below 500mA.

I’m aware that the power meter will drop some voltage and that may cause problems in itself. I’m also aware that if the pHAT really needs half an amp, there won’t be enough left off a USB port to run the pi.

However, given that it’s hot and I’m expecting only a little more than 6*30mA = 180mA extra current draw for the LEDs, I’m reluctant to feed it a decent 3A power supply.

The only unusual thing I did that isn’t in the instructions is to mount the header slightly off the board to give ~1.5mm extra height with the pins almost flush on the top side. I have tapped out the continuity from header to solder joint for all the pins shown on and I have run a screwdriver between each pair of pins to flake off the flux - no shorts. It isn’t my neatest soldering but I thought it was OK…

How much current should it draw? Is it normal for all lights to come on before boot is done?

Thanks, m

Can I get the schematic for the touch pHAT anywhere, so I can start guessing what the cause might be?