Of course, silly me! There are lots of other capacitors on the schematic in parallel with C84.1.What instrument are you using to measure the capacitor and have you removed the capacitor from the board? Most instruments cannot measure components when connected to other components.
Thanks for that. Yes, measured it and it's just a few mV, ditto the 1V8 supply on PP9, so it's pretty clear that the MXL7704-R3 PMIC is dead. After a bit of research I think that, given the difficulty of obtaining this chip and the near impossibility of replacing it without specialist soldering tools, that the rpi is dead, rip (pun intended).2. Measure the voltage on the 3.3 Volt pin of the GPIO header. If it is not close to 3.3 Volts the switching regulator IC is dead. Usually caused by accidentally shorting the 3.3 Volt pin to the zero Volt rail (commonly called GND). Be careful when probing the 3.3 Volt pin as bridging that to a neighbouring pin with the probe tip even for a fraction of a second will kill the IC if it was still alive.
And I'm still no clearer to understanding if my PS/lead combination is the cause of it. I'm inclined to think it was so probably won't risk using the PS to power the replacement rpi4. Instead I'm thinking of getting a bigger 12V supply and a 12V-5V DC-DC converter, defence in depth so to speak, but not cheap at £60 for the two... (I need a 12V supply in the system anyway for powering relays but the one I have at the moment does not have enough current to do the 5V as well.)
Unless someone can recommend a RELIABLE 5V DIN rail mount PS?
Thanks.
Statistics: Posted by johnericsutton — Sat Jan 20, 2024 10:41 am