LCD Replacement for the Macintosh Portable

[Froggy814]

Finally was able to export my code today! Hopefully it works. Unfortunantly I followed a schematic blindly and need to figure out how to supply 3v to the rp2350... The part I got isn't outputting anything! Hopefully I can just replace it with another of his 10 buddy's and see if it works then.

 

[Froggy814]

I plugged my RP2350 board into my computer, I am supplying external 3v3 power because what I put on didn't work. (Don't follow instructions blindly. Double check.) I but when I turn on the power, nothing happens. Zip, NADA, Zilch. No power pulled, not showing up on my laptop, even in device manager. No file explorer popping up when I hold the bootselect and then turn it on. I double checked the schematic, and that power is getting to where it needs to. I am even getting 1V out of the generator. I don't know what is wrong, if you can give me any pointers that would be appreciated.


P.S. It could be that the RP2350 is dead. I applyed some serious heat when I first put it on the board, but would it still generate 1V if it was dead? And how is it generating Voltage without drawing any amps, so confused

 

[liamur]

My first guess would be issues with soldering the QFN to the board. It's impressive that you did that yourself, but your chances of success are unfortunately pretty low. There is of course the risk of heat damage, but there's also a good chance you didn't get every pin contacting the board well, or shorted some pads in the soldering process.

Make sure you have a pull-up resistor on the RUN pin, otherwise the chip will be in an indeterminate state all the time, and it won't show up on USB even if you power it on in bootloader mode. I've gotten burned by this one.

I'm inclined to suspect that it is a soldering issue. If you have an external 3V3 source connected and it shows no load, then either the chip sips power in whatever state it's in (this is possible, if it's in reset then I doubt it's using much power, but RPi isn't known for extreme power efficiency), or the chip isn't connected to the supply or is broken. Also, be careful connecting it to your computer with the external supply. You probably want to remove the 3V3 regulator or cut the traces going to it so there's no risk of backpowering the computer or blowing up the regulator.

 

[Froggy814]

Where would the pull up go here? I would assume that you would put it on the RP2350 side and put it to power?

 

[Froggy814]

Also, be careful connecting it to your computer with the external supply. You probably want to remove the 3V3 regulator or cut the traces going to it so there's no risk of backpowering the computer or blowing up the regulator.

Yup! Thanks for confirming, I already did that, I took out the regulator, now they are only connected through GND! I didn't think it would be good for the regulator to be in when it has external power. Boy am I glad I got a buck converter as a power supply for testing things, really handy!

 

[liamur]

View attachment 102008

Where would the pull up go here? I would assume that you would put it on the RP2350 side and put it to power?

Correct.

 

[Froggy814]

Do you know what value? I would assume 1k ohms.

 

[liamur]

I would recommend 10kohms. If you use 1k there, you'll make a voltage divider that puts 3.3/2=1.65V on RUN, which is between the -0.3 to 0.8V range for digital low and 2 to 3.6V range for digital high as specified in the datasheet at IOVDD=3.3V, and you won't get consistent results. 10k is also a good default pull-up resistor value.

 

[Froggy814]

Cool, I'll try that. Thank you very much!